+
+
+The Internet Domain Name System (DNS) consists of the syntax to specify the names of entities in the Internet in a hierarchical manner, the rules used for delegating authority over names, and the system implementation that actually maps names to Internet addresses. DNS data is maintained in a group of distributed hierarchical databases.
+
+
+The Berkeley Internet Name Domain (BIND) implements an Internet nameserver for a number of operating systems. This document provides basic information about the installation and care of the Internet Software Consortium (ISC) BIND version 9 software package for system administrators.
+
+
+In this document,
+Section 1
+ introduces the basic DNS and BIND concepts.
+Section 2
+ describes resource requirements for running BIND in various environments. Information in
+Section 3
+ is
+task-oriented
+ in its presentation and is organized functionally, to aid in the process of installing the BINDv9 software. The task-oriented section is followed by
+Section 4
+, which contains more advanced concepts that the system administrator may need for implementing certain options. The contents of
+Section 5
+ are organized as in a reference manual to aid in the ongoing maintenance of the software.
+Section 6
+ addresses security considerations, and
+Section 7
+ contains troubleshooting help. The main body of the document is followed by several
+Appendices
+ which contain useful reference information, such as a
+Glossary
+ and a
+Bibliography
+, as well as historic information related to BIND and the Domain Name System.
+
+
+1.4 Discussion of Domain Name System (DNS) Basics and BIND
+
+
+
+
+The purpose of this document is to explain the installation and basic upkeep of the BIND software package, and we begin by reviewing the fundamentals of the domain naming system as they relate to BIND. BIND consists of a
+nameserver
+ (or "daemon") called
+named
+ and a
+resolver
+ library. The BIND server runs in the background, servicing queries on a well known network port. The standard port for UDP and TCP, usually port 53, is specified in
+ /etc/services
+. The
+resolver
+ is a set of routines residing in a system library that provides the interface that programs can use to access the domain name services.
+
+
+A nameserver (NS) is a program that stores information about named resources and responds to queries from programs called
+resolvers
+ which act as client processes. The basic function of an NS is to provide information about network objects by answering queries.
+
+
+
+With the nameserver, the network can be broken into a hierarchy of domains. The name space is organized as a tree according to organizational or administrative boundaries. Each node of the tree, called a domain, is given a label. The name of the domain is the concatenation of all the labels of the domains from the root to the current domain. This is represented in written form as a string of labels listed from right to left and separated by dots. A label need only be unique within its domain. The whole name space is partitioned into areas called
+zones
+, each starting at a domain and extending down to the leaf domains or to domains where other zones start. Zones usually represent administrative boundaries. For example, a domain name for a host at the company
+Example, Inc.
+ would be:
+
+
+The top level domain for corporate organizations is
+com
+;
+example
+ is a subdomain of
+.com
+; and
+ourhost
+ is the name of the host.
+
+
+
+The specifications for the domain nameserver are defined in RFC1034, RFC1035 and RFC974. These documents can be found in
+
+/usr/src/etc/named/doc
+ in 4.4BSD or are available via
+FTP
+ from
+
+ftp://www.isi.edu/in-notes/
+ or via the Web at
+http://www.ietf.org/rfc/
+. (See Appendix C for complete information on finding and retrieving RFCs.) It is also recommended that you read the related
+man
+ pages:
+named
+ and
+resolver
+.
+
+
+As we stated previously, a zone is a point of delegation in the DNS tree. A zone consists of those contiguous parts of the domain tree for which a domain server has complete information and over which it has authority. It contains all domain names from a certain point downward in the domain tree except those which are delegated to other zones. A delegation point has one or more NS records in the parent zone, which should be matched by equivalent NS records at the root of the delegated zone (i.e., the "@" name in the zone file).
+
+
+
+To properly operate a nameserver, it is important to understand the difference between a
+zone
+ and a
+domain
+.
+
+
+
+As an example, consider the
+example.com
+ domain, which includes names such as
+host.aaa.example.com
+and
+host.bbb.example.com
+ even though the
+example.com
+ zone includes only delegations for the
+aaa.example.com
+ and
+bbb.example.com
+ zones. A zone can map exactly to a single domain, but could also include only part of a domain, the rest of which could be delegated to other nameservers. Every name in the DNS tree is a
+domain
+, even if it is
+terminal
+, that is, has no
+subdomains
+. Every subdomain is a domain and every domain except the root is also a subdomain. The terminology is not intuitive and it is suggested that you read RFCs 1033, 1034, and 1035 to gain a complete understanding of this difficult and subtle topic.
+
+
+
+Though BIND is a Domain Nameserver, it deals primarily in terms of zones. The primary and secondary declarations in the
+named.conf
+ file specify zones, not domains. When you ask some other site if it is willing to be a secondary server for your
+domain
+, you are actually asking for secondary service for some collection of zones.
+
+
+
+Each zone will have one
+primary master
+ (also called
+primary
+) server which loads the zone contents from some local file edited by humans or perhaps generated mechanically from some other local file which is edited by humans. There there will be some number of
+secondary master
+servers, which load the zone contents using the DNS protocol (that is, the secondary servers will contact the primary and fetch the zone data using TCP). This set of servers--the primary and all of its secondaries--should be listed in the NS records in the parent zone and will constitute a
+delegation
+. This set of servers must also be listed in the zone file itself, usually under the
+@
+ name which indicates the
+top level
+ or
+root
+ of the current zone. You can list servers in the zone's top-level
+@
+ NS records that are not in the parent's NS delegation, but you cannot list servers in the parent's delegation that are not present in the zone's
+@
+.
+
+
+
+Any servers listed in the NS records must be configured as
+
+authoritative for the zone. A server is authoritative for a zone when it has been configured to answer questions for that zone with authority, which it does by setting the "authoritative answer" (AA) bit in reply brackets. A server may be authoritative for more than one zone. The authoritative data for a zone is composed of all of the Resource Records (RRs)--the data associated with names in a tree-structured name space--attached to all of the nodes from the top node of the zone down to leaf nodes or nodes above
+
+cuts around the bottom edge of the zone.
+
+
+
+Adding a zone as a type primary or type slave will tell the server to answer questions for the zone authoritatively. If the server is able to load the zone into memory without any errors it will set the AA bit when it replies to queries for the zone. See RFCs 1034 and 1035 for more information about the AA bit.
+
+
+A DNS server can be primary for some zones and secondary for others or can be only a primary, or only a secondary, or can serve no zones and just answer queries via its
+cache
+. Primary servers are often also called
+masters
+ and secondary servers are often also called
+slaves
+. Both primary/master and secondary/slave servers are authoritative for a zone.
+
+
+
+All servers keep data in their cache until the data expires, based on a TTL (Time To Live) field which is maintained for all resource records.
+
+
+The
+primary master
+ server is the ultimate source of information about a domain. The primary master is an authoritative server configured to be the source of zone transfer for one or more secondary servers. The primary master server obtains data for the zone from a file on disk.
+
+
+A
+slave server
+, also called a
+secondary server
+, is an authoritative server that uses zone transfers from the primary master server to retrieve the zone data. Optionally, the slave server obtains zone data from a cache on disk. Slave servers provide necessary redundancy. All secondary/slave servers are named in the NS resource records (RRs) for the zone.
+
+
+Some servers are
+caching only servers
+. This means that the server caches the information that it receives and uses it until the data expires. A caching only server is a server that is not authoritative for any zone. This server services queries and asks other servers, who have the authority, for the information it needs.
+
+
+Instead of interacting with the nameservers for the root and other domains, a
+forwarding server
+ always forwards queries it cannot satisfy from its authoritative data or cache to a fixed list of other servers. The forwarded queries are also known as
+recursive queries,
+the same type as a client would send to a server. There may be one or more servers forwarded to for a given zone and they are queried in turn until the list is exhausted. A forwarding server is typically used when you do not wish all the servers at a given site to interact with the rest of the Internet servers. A typical scenario would involve a number of internal DNS servers, and an internet firewall. The servers which cannot pass packets through the firewall would forward to the server which can, which would ask the internet DNS servers on the internal server's behalf. An added benefit of using the forwarding feature is that the central machine develops a much more complete cache of information that all the workstations can take advantage of.
+
+
+
+There is no prohibition against declaring a server to be a forwarder even though it has primary and/or secondary zones as well; the effect will still be that anything in the local server's cache or zones will be answered, and anything else will be forwarded using the forwarders list.
+
+
+A
+
+stealth server is a primary master server that is neither listed in any root zone files nor advertised as being a server. It is set up to hide the true master server for a zone in order to provide some measure of security, or protect the zone from
+
+Denial of Service (
+
+DoS) attacks, or reduce the load on the main server, or any number of other reasons. It is also used to provide some measure of network redundancy. Slave servers load zone data from it.
+
+
+DNS hardware requirements have traditionally been quite modest. For many installations, servers that have been pensioned off from active duty have performed admirably as DNS servers.
+
+
+
+The DNSSEC and IPv6 features of BINDv9 may prove to be quite CPU intensive however, so organizations that make heavy use of these features may wish to consider larger systems for these applications. BINDv9 is now fully multithreaded, allowing full utilization of multiprocessor systems, for installations that need it.
+
+
+CPU requrements for BINDv9 start at i486 for serving of static zones without caching, to enterprise-class machines if you intend to process many dynamic updates and DNSSEC signed zones, serving many thousands of queries per second.
+
+
+For BIND 8.x and older versions, the memory of the server had to be large enough to fit the cache and zones loaded off disk. BINDv9 will provide methods to set resource limits, at the expense of limiting the cache and causing more DNS traffic. It is still good practice to have enough memory to load all zone and cache data into memory--unfortunately, the best way to determine this for a given installation is to watch the nameserver in operation. After a few weeks, the server process should reach a relatively stable size where entries are expiring from the cache as fast as they are being inserted. Ideally, the resource limits for BINDv9 should be set higher than this stable size.
+
+
+For nameserver intensive environments, there are two alternative configurations that may be used. The first is where clients and any second-level internal nameservers query a main nameserver, which has enough memory to build a large cache. This approach minimizes the bandwidth used by external name lookups. The second alternative is to set up second-level internal nameservers to make queries independently. In this configuration, none of the individual machines needs to have as much memory or CPU power as in the first alternative, but this has the disadvantage of making many more external queries, as none of the nameservers share their cached data.
+
+
+
+
+
+
+2.5 Operating Systems Supported by the Internet Software Consortium
+
+
+
+
+ISC BINDv9 compiles and runs on the following operating systems:
+
+
+In this section we provide some suggested configurations along with guidelines for their use. We also address the topic of reasonable option setting.
+zone "example.com" { // Example zone for "example.com".
+type master; // It's a master zone.
+file "m/example.com.db"; // The file is here.
+allow-query { any; }; // Allow anyone to query.
+allow-transfer { corpnet; }; // Only allow corp nets to transfer zone.
+};
+
+
+
+zone "offsite.example.com" { // Example zone for an off-site corp zone.
+type slave; // It's a slave zone.
+masters { 192.168.4.12; }; // The master is at this address.
+file "s/offsite.example.com.db"; // The file is here.
+notify no; // Don't worry about NOTIFY
+ing.
+allow-query { any; }; // Allow anyone to query.
+;
+
+
+Primitive load balancing can be achieved in DNS using multiple A records for one name.
+
+
+
+For example, if you have three WWW servers with network addresses of 10.0.0.1, 10.0.0.2 and 10.0.0.3, a record like the following means that clients will connect to each machine one third of the time:
+
+
+When a resolver queries for these records, BIND will rotate them and respond to the query with the records in a different order. This is known as cyclic or round-robin ordering.In the example above, the first client will receive the records in the order 1,2,3; the second client will receive them in the order 2,3,1; and the third 3,1,2. Most clients will use the first record returned, and discard the rest.
+
+
+
+For more detail on ordering responses, check the
+rrset-order
+ substatement in the
+options
+ statement in
+RRset Ordering
+.
+
+
+DNS Notify is a mechanism that allows master nameservers to notify their slave servers of changes to a zone's data and that a query should be initiated to discover the new data. DNS Notify is turned on by default.
+
+
+
+DNS Notify is fully documented in RFC 1996. See also the description of the zone option
+also-notify
+ in section 3.1.3.7, "Zone transfers."
+
+
+3.4.1 Tools for Use With the Nameserver Daemon
+
+
+
+
+There are several indispensable diagnostic, administrative and monotoring tools available to the system administrator for controlling and debugging the nameserver daemon. We describe several in this section
+
+
+The domain information groper (
+dig
+) is a command line tool that can be used to gather information from the Domain Name System servers. Dig has two modes: simple interactive mode for a single query, and batch mode which executes a query for each in a list of several query lines. All query options are accessible from the command line.
+
+
+The
+
+
+host
+
+
+utility provides a simple DNS lookup using a command-line interface for looking up Internet hostnames. Bu default, the utility interprets between host names and Internet addresses, but its functionality can be extended with the use of options.
+
+
+
+nslookup
+ is a program used to query Internet domain nameservers. nslookup has two modes: interactive and non-interactive. Interactive mode allows the user to query nameservers for information about various hosts and domains or to print a list of hosts in a domain. Non-interactive mode is used to print just the name and requested information for a host or domain.
+
+
+Interactive mode is entered when no arguments are given (the default nameserver will be used) or when the first argument is a hyphen (-) and the second argument is the host name or Internet address of a nameserver.
+
+
+
+Non-interactive mode is used when the name or Internet address of the host to be looked up is given as the first argument. The optional second argument specifies the host name or address of a nameserver.
+
+
+
+The options listed under the "set" command (see the nslookup man page for details) can be specified in the .nslookuprc file in the user's home directory if they are listed one per line. Options can also be specified on the command line if they precede the arguments and are prefixed with a hyphen. For example, to change the default query type to host information, and the initial time-out to 10 seconds, type:
+
+nslookup -query=hinfo -timeout=10
+
+
+
+For more information and a list of available commands and options, see the nslookup man page.
+
+
+The name daemon control (
+ndc
+) program is a shell script utility that allows the system administrator to control the operation of a nameserver. If you run ndc without any options it will display a usage message and prompt for commands until it reads EOF. Several commands are built into ndc, but the full set of commands supported by the nameserver is dynamic and should be discovered using the "help" command. Read the man page for ndc for details on its command syntax.
+
+
+
+MRTG
+ is primarily a router traffic grapher, but can be used to monitor BIND DNS servers, as well. The `stat' script, supplied with MRTG in the MRTG `contrib/stat' directory, can be used to monitor numbers of queries, and counts of various sorts of responses.
+
+
+Dynamic update is the term used for the ability under certain specified conditions to add, modify or delete records or RRsets in the master zone files. Dynamic update is fully described in RFC 2136.
+
+
+
+Dynamic update is enabled by including an
+allow-update{}
+ clause in the zone declaration. You should allow as few hosts as possible to update your DNS because there is no per-RR security. If a client is authorized to update your DNS, it can do anything with the zone file, including deleting most of the contents or replacing records with different ones. For this reason, many sites delegate a zone which can be dynamically updated, rather than allowing their uppermost domain to be dynamic.
+
+
+
+Once a zone has been made dynamic, changes can no longer be made by hand without stopping BIND, editing the zone and then restarting BIND. This is to prevent an update being lost, either by the zone file being changed by hand and overwritten immediately by a dynamic update without being reread, or having a handwritten zone file overwrite a dynamic update that has occurred while the zone file was being hand-edited.
+
+
+If dynamic update is enabled, and incremental transfer (IXFR) is also enabled, BIND will maintain a list of changes for secondary servers to transfer, instead of having to transfer the entire zone file.
+
+
+
+IXFR is enabled globally by giving a filename for
+ixfr-base
+ and
+ixfr-tmp-file
+, and
+maintain-ixfr-base true
+. A server statement with the
+use-ixfr
+ option set to
+true
+ will then enable incremental transfers to that server.
+
+
+
+IXFR can only track changes made to the zone with dynamic update - no changes can be made by editing the zone file, even with the stop-start procedure above.
+
+
+Setting up different views, or visibility, of DNS space to internal , as opposed to external, resolvers is usually referred to as a "Split DNS" or "Split Brain DNS" setup. There are several reasons an organization would want to set its DNS up this way.
+
+
+
+One common reason for setting up a DNS system this way is to hide "internal" DNS information from "external" clients on the Internet. There is some debate as to whether or not this is actually useful. Internal DNS information leaks out in many ways (via e-mail headers, for example) and most savvy "attackers" can find the information they need using other means.
+
+
+
+Another common reason for setting up a Split DNS system is to allow internal networks that are behind filters or RFC1918 space (reserved IP space, as documented in RFC 1918) to resolve DNS on the Internet. Split DNS can also be used to allow mail from outside back in to the internal network.
+
+
+Let's say a company named
+Example, Inc.
+ (example.com) has several corporate sites that have an internal network with reserved IP space and an external DMZ (the demilitarized zone, or "outside" section of a network) that is available to the public.
+
+
+
+
+Example, Inc.
+ wants its internal clients to be able to resolve external hostnames and to exchange mail with people on the outside. The company also wants its internal resolvers to have access to certain internal-only zones that are not available at all outside of the internal network.
+
+
+
+In order to accomplish this, the company will set up two sets of nameservers. One set will be on the inside network (in the reserved IP space) and the other set will be on bastion hosts, which are "proxy" hosts that can talk to both sides of its network, in the DMZ.
+
+
+
+The internal servers will be configured to forward all queries, except queries for
+site1.example
+,
+site2.example
+,
+site1.example.com
+, and
+site2.example.com
+, to the servers in the DMZ. These internal servers will have complete sets of information for
+site1.example.com
+,
+site2.example.com
+,
+ site1.internal
+, and
+site2.internal
+.
+
+
+
+To protect the
+site1.internal
+ and
+ site2.internal
+ domains, the internal nameservers must be configured to disallow all queries to these domains from any external hosts, including the bastion hosts.
+
+
+
+The external servers, which are on the bastion hosts, will be configured to serve the "public" version of the
+site1
+ and
+site2.example.com
+ zones. This could include things such as the host records for public servers (
+www.example.com
+,
+ftp.example.com
+), and mail exchanger records (
+a.mx.example.com
+ and
+b.mx.example.com
+).
+
+
+
+In addition, the public
+site1
+ and
+site2 .example.com
+ zones should have special MX records that contain wildcard (*) records pointing to the bastion hosts. This is needed because external mail servers do not have any other way of looking up how to deliver mail to those internal hosts. With the wildcard records, the mail will be delivered to the bastion host, which can then forward it on to internal hosts.
+
+
+Now that they accept mail on behalf of anything in the internal network, the bastion hosts will need to know how to deliver mail to internal hosts. In order for this to work properly, the resolvers on the bastion hosts will need to be configured to point to the internal nameservers for DNS resolution.
+
+
+
+Queries for internal hostnames will be answered by the internal servers, and queries for external hostnames will be forwarded back out to the DNS servers on the bastion hosts.
+
+
+
+In order for all this to work properly, internal clients will need to be configured to query
+only
+ the internal nameservers for DNS queries. This could also be enforced via selective filtering on the network.
+
+
+
+If everything has been set properly,
+Example, Inc.
+'s internal clients will now be able to:
+
+
+
+
+Look up any hostnames in the
+site1
+ and
+site2 .example.com
+ zones.
+
+
+
+Look up any hostnames in the
+site1.internal
+ and
+site2.internal
+ domains.
+
+
+Look up any hostnames in the
+site1
+ and
+site2 .example.com
+zones.
+
+
+
+Exchange mail with anyone in the
+site1
+ and
+site2 .example.com
+ zones.
+
+
+
+
+Here is an example configuration for the setup we just described above. Note that this is only configuration information; see
+Sample Configuration and Logging
+ for information on how to configure your zone files.
+
+
+Information about TSIG in this section was provided by Brian Wellington of TISLabs. This is a short guide to setting up TSIG based transaction security in BIND. It describes changes to the configuration file as well as what changes are required for different features, including the process of creating transaction keys and using transaction signatures with BIND.
+
+
+
+BIND primarily supports TSIG for server-server communication. This includes zone transfer, notify, and recursive query messages. The resolver bundled with BIND 8.2 has limited support for TSIG, but it is doubtful that support will be integrated into any client applications. There cannot be support for TSIG in stub resolvers, since storing secret keys in
+/etc/resolv.conf
+ is highly insecure.
+
+
+
+TSIG might be most useful for dynamic update. A primary server for a dynamic zone should use access control to control updates, but IP-based access control is insufficient. Key-based access control is far superior (see
+draft-ietf-dnsind-simple-secure-update-02.txt
+). The
+nsupdate
+ program that is shipped with BIND supports TSIG via the "
+-k
+" command line option.
+
+
+
+
+
+4.3.1 Generate Shared Keys for Each Pair of Hosts
+
+
+
+
+A shared secret is generated to be shared between host1 and host2. The key name is chosen to be "host1-host2.", which is arbitrary. The key name be the same on both hosts.
+
+
+The following command will generate a 128 bit (16 byte) HMAC-MD5 key as described above. Longer keys are better, but shorter keys are easier to read. Note that the maximum key length is 512 bits; keys longer than that will be digested with MD5 to produce a 128 bit key.
+
+
+The key is in the file "Khost1-host2.+157+00000.private". Nothing actually uses this file, but the base64 encoded string following "Key:" can be extracted:
+
+
+The shared secret is simply a random sequence of bits, encoded in base64. Most ASCII strings are valid base64 strings (assuming the length is a multiple of 4 and only valid characters are used), so the shared secret can be manually generated.
+
+
+
+Also, a known string can be run through mmencode or a similar program to generate base64 encoded data.
+
+
+
+
+
+
+
+4.3.2 Copying the Shared Secret to Both Machines
+
+
+
+
+This is beyond the scope of DNS. A secure transport mechanism should be used. This could be secure FTP, ssh, telephone, etc.
+
+
+
+
+
+
+4.3.3 Informing the Servers of the Key's Existence
+
+
+
+
+Imagine host1 and host 2 are both servers. The following is added to each server's named.conf file:
+
+
+The algorithm, hmac-md5, is the only one supported by BIND. The secret is the one generated above. Since this is a secret, it is recommended that either
+named.conf
+ be non-world readable, or the key directive be added to a non-world readable file that's included by named.conf.
+
+
+
+At this point, the key is recognized. This means that if the server receives a message signed by this key, it can verify the signature. If the signature succeeds, the response is signed by the same key.
+
+
+Since keys are shared between two hosts only, the server must be told when keys are to be used. The following is added to host1's named.conf file, if host2's IP address is 10.1.2.3:
+
+server 10.1.2.3 {
+ keys {host1-host2.;};
+};
+
+
+
+Multiple keys may be present, but only the first is used. This directive does not contain any secrets, so it may be in a world-readable file.
+
+
+
+If host1 sends a message that is a response to that address, the message will be signed with the specified key. host1 will expect any responses to signed messages to be signed with the same key.
+
+
+
+A similar statement must be present in host2's configuration file (with host1's address) for host2 to sign non-response messages to host1.
+
+
+BIND allows IP addresses and ranges to be specified in ACL definitions and
+allow-{query|transfer|update}
+ directives. This has been extended to allow TSIG keys also. The above key would be denoted
+key host1-host2
+.
+
+
+
+An example of an allow-update directive would be:
+
+allow-update {key host1-host2.;};
+
+
+
+This allows dynamic updates to succeed only if the request was signed by a key named "host1-host2."
+
+
+The processing of TSIG signed messages can result in several errors. If a signed message is sent to a non-TSIG aware server, a FORMERR will be returned, since the server will not understand the record. This is a result of misconfiguration, since the server must be explicitly configured to send a TSIG signed message to a specific server.
+
+
+
+If a TSIG aware server receives a message signed by an unknown key, the response will be unsigned with the TSIG extended error code set to BADKEY. If a TSIG aware server receives a message with a signature that does not validate, the response will be unsigned with the TSIG extended error code set to BADSIG. If a TSIG aware server receives a message with a time outside of the allowed range, the response will be signed with the TSIG extended error code set to BADTIME, and the time values will be adjusted so that the response can be successfully verified. In any of these cases, the message's rcode is set to NOTAUTH.
+
+
+
+TSIG verification errors are logged by the server as
+
+
+Cryptographc authentication of DNS information is made possible through the DNS Security (DNSSEC) extension to the domain system. This describes the processing of creating and using DNSSEC signed zones. The zones used in this exercise will be "dnssec.example" and "sub.dnssec.example."
+
+
+The
+.key
+ files contain public keys in DNS RR format, which is base 64. The
+.private
+ files contain private keys, with each field encoded in base 64.
+
+
+Edit the zone files if desired (to move and/or format KEY records, etc.). This is also a good time to add
+$ORIGIN
+ directives to the zone files if they aren't present.
+
+
+The following command uses the zone.dnssec.example as input and creates the zone.dnssec.example.signed file. The key used is the dsa key for dnssec.example with id 64555 (-ki), and statistics are printed (-st). Parent files are generated for each child zone (-ps), and no global parent file is produced (-no-p1).
+
+
+The following command is similar to the previous one. The main difference is that the input parent file sub.dnssec.example..PARENT is specified (-pi) in addition to the input zone file; this file was generated by the previous call to the signer. Also, the -ps and -no-p1 options are omitted since there are no child zones of this zone. If this zone had child zones, these options should be present.
+
+
+Step 5: Enter the top-level zone key in the named.conf file for the master server.
+
+
+
+
+The public key for the top-level signed zone must be present in named.conf, so that the server can verify the data on load (it must be able to traverse a keychain and end at a trusted key). This key is added in a zone pubkey directive (which has a format similar to a KEY record, but not identical). Note that this is not needed for the subzone, as its key is signed by the trusted key in the parent zone.
+
+
+
+This uses the key from Kdnssec.example.+003+64555.key
+
+
+IPv6 addresses are 128-bit identifiers for interfaces and sets of interfaces which were introduced in the DNS to facilitate scalable Internet routing. There are three types of addresses:
+Unicast
+, an identifier for a single interface;
+Anycast
+, an identifier for a set of interfaces; and
+Multicast
+, an identifier for a set of interfaces. Here we describe the global Unicast address scheme. For more information, see RFC 2374.
+
+
+
+The aggregatable global Unicast address format is as follows:
+
+
+The `Public Topology' is provided by the upstream provider or ISP, and (roughly) corresponds to the IPv4 `network' section of the address range. The `Site Topology' is where you can subnet this space, much like subnetting an IPv4 class A or B network into class Cs. The `Interface Identifier' is the address of an individual interface on a given network. (With IPv6, addresses belong to interfaces rather than machines.)
+
+
+
+The subnetting capability of IPv6 is much more flexible than that of IPv4: subnetting can now be carried out on bit boundaries, in much the same way as Classless InterDomain Routing (CIDR).
+
+
+
+The internal structure of the `Public Topology' for an A6 global unicast address consists of:
+
+
+24 bits for Next Level Aggregators. This allows organizations with a TLA to hand out portions of their IP space to client organizations, so that the client can then split up the network further by filling in more NLA bits, and hand out IPv6 prefixes to their clients, and so forth.
+
+
+
+There is no particular structure for the `Site topology' section. Organizations can allocate these bits in any way they desire, in the same way as they would subnet an IPv4 class A (8 bit prefix) network.
+
+
+
+The Interface identifier must be unique on that network. On ethernet networks, one way to ensure this is to set the address to the first three bytes of the hardware address, `FFFE', then the last three bytes of the hardware address. The lowest significant bit of the first byte should then be complemented. Addresses are written as 32-bit blocks separated with a colon, and leading zeros of a block may be omitted, for example:
+
+3ffe:8050:201:9:a00:20ff:fe81:2b32
+
+
+
+IPv6 address specifications are likely to contain long strings of zeros, so the architects have included a shorthand for specifying them. The double colon `::' indicates the longest possible string of zeros that can fit, and can be used only once in an address.
+
+
+Forward name lookups (host name to IP address) under IPv6 do not necessarily return the complete IPv6 address of the host. Because the provider-assigned prefix may change, the A6 record can simply specify the locally assigned portion of the name, and refer to the provider for the remainder.
+
+
+
+A complete IPv6 A6 record that provides the full 128 bit address looks like:
+
+
+Note that the number preceding the address is the number of bits to be provided via the referral. This is probably the easiest way to roll out an IPv6 installation, though you may wish to provide a reference to your provider assigned prefix:
+
+
+The referral where there are no more bits is to `.', the root zone. Be warned that excessive use of this chaining can lead to extremely poor name resolution for people trying to access your hosts.
+
+
+Reverse IPv6 addresses may appear as one or more hex strings, known as "bitstring labels," each followed by a number of valid bits. A full 128 bits may be specified at the ip6.int top level, or more likely, the provider will delegate you a smaller chunk of addresses for which you will need to supply reverse DNS.
+
+
+
+The address can be split up along arbitrary boundaries, and is written with hex numbers in forward order, rather than in reverse order as IPv4 PTR records are written. The sections between dot separators are reversed as usual. If the number of valid bits in the hex string is less than the string specifies, it is the
+first N bits
+ that are counted. Thus, \[x2/3] gives a bit pattern of 0010, the first three bits of which, 001, are valid.
+
+
+
+\[x00090A0020FFFE812B32/80].\[xFFF402801008/45].\[x2/3].ip6.int.
+ (divided into FP, TLA/RES/NLA, and local)
+
+
+
+
+\[x00090A0020FFFE812B32/80].\[x80500201/32].\[xFFF0/13].\[x2/3].ip6.int.
+ (divided into FP, TLA, RES/NLA, and local)
+
+
+
+These strings are all equivalent. The combined TLA/RES/NLA in the second example bears no resemblance to any string in the address because it is offset by three bits.
+
+
+
+
+
+
+4.5.4 Using DNAME for Delegation of IPv6 Reverse Addresses
+
+
+
+
+Delegation of reverse addresses is done through the new DNAME RR. In the example above, where
+\[x2/3].ip6.int.
+ needs to delegate
+
+
+\[xFFF0]
+
+
+to an organization (
+example2.com
+), the domain administrator would insert a line similar to the following in the
+\[x2/3].ip6.int.
+ zone:
+
+$ORIGIN \[x2/3].ip6.int.
+\[xFFF0/13] 1h IN DNAME ip6.example2.com.
+
+
+
+
+example2.com
+ would then place into the
+ip6
+zone:
+
+$ORIGIN ip6.example.com.
+\[x80500201/32] 1h IN DNAME ip6.example.com.
+
+
+
+Finally,
+example.com
+needs to include in the
+ip6.example.com
+ zone:
+
+$ORIGIN ip6.example.com.
+\[x00090A0020FFFE812B32/80] 1h IN PTR host.example.com.
+
+
+
+We suggest that the top of your administrative control (
+example.com
+, in this case) provide all the bits required for reverse and forward resolution to allow name resolution even if the network is disconnected from the Internet. This will also allow operation with DNSSEC if you set up a false trusted server for "." containing only delegations for your forward and reverse zones directly to the top of your administrative control. This should be signed with a key trusted by all of your clients, equivalent to the real key for "
+.
+".
+
+
+BINDv9 configuration is broadly similar to BIND 8.x; however, there are a few new areas of configuration, such as views. BIND 8.x configuration files should work with few alterations in BINDv9, although more complex configurations should be reviewed to check if they can be more efficiently implemented using the new features found in BINDv9.
+
+
+
+BIND 4.9.x configuration files can be converted to the new format by using
+
+src/bin/named/named-bootconf.pl
+, a shell script that is part of the BIND release kit.
+
+
+An IP port
+number
+.
+number
+ is limited to 0 through 65535, with values below 1024 typically restricted to root-owned processes. In some cases an asterisk (*) character can be used as a placeholder to select a random high-numbered port.
+
+
+An IP network specified in
+dotted-decimal
+ form, followed by "/'' and then the number of bits in the netmask. E.g.
+127/8
+ is the network
+127.0.0.0
+ with netmask
+255.0.0.0
+ and
+1.2.3.0/28
+ is network
+1.2.3.0
+ with netmask
+255.255.255.240
+.
+
+
+A non-negative integer with an entire range limited by the range of a C language signed integer (2,147,483,647 on a machine with 32 bit integers). Its acceptable value might further be limited by the context in which it is used.
+
+
+A number, the word
+unlimited
+, or the word
+default
+.
+
+
+
+The maximum value of
+size_spec
+ is that of unsigned long integers on the machine.
+unlimited
+ requests unlimited use, or the maximum available amount.
+default
+ uses the limit that was in force when the server was started.
+
+
+
+A
+number
+ can optionally be followed by a scaling factor:
+K
+ or
+k
+for kilobytes,
+M
+ or
+m
+ for megabytes, and
+G
+ or
+g
+ for gigabytes, which scale by 1024, 1024*1024, and 1024*1024*1024 respectively.
+
+
+
+Integer storage overflow is currently silently ignored during conversion of scaled values, resulting in values less than intended, possibly even negative. Using
+unlimited
+ is the best way to safely set a really large number.
+
+
+Address match lists are primarily used to determine access control for various server operations. They are also used to define priorities for querying other nameservers and to set the addresses on which named will listen for queries. The elements which constitute an address match list can be any of the following:
+
+
+Elements can be negated with a leading exclamation mark ("!"), and the match list names "any", "none", "localhost" and "localnets" are predefined. More information on those names can be found in the description of the acl statement.
+
+
+
+The addition of the key clause made the name of this syntactic element something of a misnomer, since security keys can be used to validate access without regard to a host or network address. Nonetheless, the term "address match list" is still used throughout the documentation.
+
+
+
+When a given IP address or prefix is compared to an address match list, the list is traversed in order until an element matches. The interpretation of a match depends on whether the list is being used for access control, defining listen-on ports, or as a topology, and whether the element was negated.
+
+
+
+When used as an access control list, a non-negated match allows access and a negated match denies access. If there is no match, access is denied. The clauses allow-query, allow-transfer, allow-update and blackhole all use address match lists like this. Similarly, the listen-on option will cause the server to not accept queries on any of the machine's addresses which do not match the list.
+
+
+
+When used with the topology clause, a non-negated match returns a distance based on its position on the list (the closer the match is to the start of the list, the shorter the distance is between it and the server). A negated match will be assigned the maximum distance from the server. If there is no match, the address will get a distance which is further than any non-negated list element, and closer than any negated element.
+
+
+
+Because of the first-match aspect of the algorithm, an element that defines a subset of another element in the list should come before the broader element, regardless of whether either is negated. For example, in
+
+1.2.3/24; ! 1.2.3.13;
+ the 1.2.3.13 element is completely useless because the algorithm will match any lookup for 1.2.3.13 to the 1.2.3/24 element. Using
+! 1.2.3.13; 1.2.3/24
+ fixes that problem by having 1.2.3.13 blocked by the negation but all other 1.2.3.* hosts fall through.
+
+
+The BINDv9 comment syntax allows for comments to appear anywhere that white space may appear in a BIND configuration file. To appeal to programmers of all kinds, they can be written in C, C++, or shell/perl constructs.
+
+
+Comments may appear anywhere that whitespace may appear in a BIND configuration file.
+
+
+
+C-style comments start with the two characters /* (slash, star) and end with */ (star, slash). Because they are completely delimited with these characters, they can be used to comment only a portion of a line or to span multiple lines.
+
+
+
+C-style comments cannot be nested. For example, the following is not valid because the entire comment ends with the first */:
+
+
+
+/* This is the start of a comment.
+ This is still part of the comment.
+/* This is an incorrect attempt at nesting a comment. */
+ This is no longer in any comment. */
+
+
+
+C++-style comments start with the two characters // (slash, slash) and continue to the end of the physical line. They cannot be continued across multiple physical lines; to have one logical comment span multiple lines, each line must use the // pair.
+
+
+// This is the start of a comment. The next line
+// is a new comment, even though it is logically
+// part of the previous comment.
+
+
+
+Shell-style (or perl-style, if you prefer) comments start with the character # (number sign) and continue to the end of the physical line, like C++ comments.
+
+
+# This is the start of a comment. The next line
+# is a new comment, even though it is logically
+# part of the previous comment.
+
+
+
+WARNING: you cannot use the ; (semicolon) character to start a comment such as you would in a zone file. The semicolon indicates the end of a configuration statement, so whatever follows it will be interpreted as the start of the next statement.
+
+
+A BINDv9 configuration consists of statements and comments. Statements end with a semicolon. Statements and comments are the only elements that can appear without enclosing braces. Many statements contain a block of substatements, which are also terminated with a semicolon.
+
+
+The
+logging
+ and
+options
+ statements may only occur once per configuration.
+logging
+ statements are read in first,
+options
+ second. Also, although the
+options
+ statement can appear anywhere in a configuration file, it is suggested that it appear at the beginning, since things like the default directory are not defined until it after it has been read.
+
+
+The
+acl
+ statement creates a
+named
+ address match list. It gets its name from a primary use of address match lists: Access Control Lists (ACLs).
+
+
+
+Note that an address match list's name must be defined with
+acl
+ before it can be used elsewhere; no forward references are allowed.
+controls {
+ [inet (ip_addr|*) port ip_port allow { address_match_list } ; [inet...;[...]]]
+
+ [unix string permission number owner number group number ; [unix...;[..]]]
+};
+
+
+
+
+
+
+5.2.4
+controls
+ Statement Definition and Usage
+
+
+
+
+The
+controls
+ statement declares control channels to be used by system administrators to affect the operation of the local nameserver. These control channels are used by the
+ndc
+ utility to send commands to and retrieve non-DNS results from a nameserver.
+
+
+
+A UNIX control channel is a "first in first out" (FIFO) named pipe in the file system, and access to it is controlled by normal file system permissions. It is created by
+named
+ with the specified file mode bits (see the
+chmod(1)
+ manual page), user and group owner. Note that, unlike
+chmod
+, the mode bits specified for
+permission
+ will normally have a leading
+0
+ so the number is interpreted as octal. Also note that the user and group ownership specified as owner and group must be given as numbers, not names. It is recommended that the permissions be restricted to administrative personnel only to prevent random users on the system from having the ability to manage the local nameserver.
+
+
+
+An
+inet
+ control channel is a TCP/IP socket accessible to the Internet, created at the specified
+ip_port
+ on the specified
+ip_addr
+. Modern telnet clients are capable of speaking directly to these sockets, and the control protocol is ARPAnet-style text. It is recommended that 127.0.0.1 be the only
+ip_addr
+ used, and this only if you trust all non-privileged users on the local host to manage your nameserver.
+
+
+5.2.6
+include
+ Statement Definition and Usage
+
+
+
+
+The
+include
+ statement inserts the specified file at the point that the
+include
+ statement is encountered. The
+include
+ statement facilitates the administration of configuration files by permitting the writing of some things but not others. For example, the statement could include private keys that are readable only by a nameserver.
+
+
+The
+key
+ statement defines a key ID which can be used in a server statement to associate an authentication method with a particular nameserver.
+
+
+
+A key ID must be created with the
+key
+ statement before it can be used in a server definition or an address match list.
+
+
+
+The
+algorithm_id
+ is a string that specifies a security/authentication algorithm. The only algorithm currently supported with tsig authentication is
+hmac-md5
+. The
+secret_string
+ is the secret to be used by the algorithm, and is treated as a base-64 encoded string.
+
+
+
+The
+key
+ statement is intended for use in transaction security. Unless included in a server statement, it is not used to sign any requests. It is used to verify requests matching the
+key_id
+ and
+algorithm_id
+, and sign replies to those requests.
+
+
+5.2.10
+logging
+ statement definition and usage
+
+
+
+
+The
+logging
+ statement configures a wide variety of logging options for the nameserver. Its
+channel
+ phrase associates output methods, format options and severity levels with a name that can then be used with the
+category
+ phrase to select how various classes of messages are logged.
+
+
+
+Only one
+logging
+ statement is used to define as many channels and categories as are wanted. If there are multiple
+logging
+ statements in a configuration, the first defined determines the logging, and warnings are issued for the others via the default
+syslog
+. If there is no
+logging
+ statement, the logging configuration will be:
+
+
+
+
+Note: these categories may change! Also, additional syntax in BINDv9 may make it possible to limit logging to particular modules.
+
+
+
+The logging configuration is established as soon as the
+logging
+ statement is parsed. If you want to redirect messages about processing of the entire configuration file, the
+logging
+ statement must appear first. Even if you do not redirect configuration file parsing messages, we recommend always putting the logging statement first so that this rule need not be consciously recalled if you ever do need or want the parser's messages relocated.
+
+
+5.2.12
+options
+ Statement Definition and Usage
+
+
+
+
+The
+options
+ statement sets up global options to be used by BIND. This statement may appear only once in a configuration file. If more than one occurrence is found, the first occurrence determines the actual options used, and a warning will be generated. If there is no
+options
+ statement, an options block with each option set to its default will be used.
+
+
+The version the server should report via the
+ndc
+ command or via a query of name
+version.bind
+ in class
+chaos
+. The default is the real version number of this server.
+
+
+The working directory of the server. Any non-absolute pathnames in the configuration file will be taken as relative to this directory. The default location for most server output files (e.g. "
+named.run
+") is this directory. If a directory is not specified, the working directory defaults to ".", the directory from which the server was started. The directory specified should be an absolute path.
+
+
+The pathname to the
+named-xfer
+ program that the server uses for inbound zone transfers. If not specified, the default is system dependent
+(e.g. "
+/usr/sbin/named-xfer
+").
+
+
+The pathname of the file the server dumps the database to when it receives
+SIGINT
+ signal (
+ndc dumpdb
+). If not specified, the default is "
+named_dump.db
+".
+
+
+The pathname of the file the server writes memory usage statistics to on exit, if
+deallocate-on-exit
+ is
+yes
+. If not specified, the default is "
+named.memstats
+".
+
+
+The pathname of the file the server writes its process ID in. If not specified, the default is operating system dependent, but is usually "/var/run/named.pid" or
+"/etc/named.pid". The pid-file is used by programs like
+ndc
+ that want to send signals to the running nameserver.
+
+
+The pathname of the file the server appends statistics to when it receives
+SIGKILL
+ signal (
+ndc stats
+). If not specified, the default is "
+named.stats
+".
+
+
+If
+yes
+, then the
+AA
+ bit is always set on NXDOMAIN responses, even if the server is not actually authoritative. The default is yes. Do not turn off
+auth-nxdomain
+ unless you are sure you know what you are doing, as some older software won't like it.
+
+
+If
+yes
+, then when the server exits it will painstakingly deallocate every object it allocated, and then write a memory usage report to the
+memstatistics-file
+. The default is
+no
+, because it is faster to let the operating system clean up.
+deallocate-on-exit
+ is handy for detecting memory leaks.
+
+
+If
+yes
+, then the server treats all zones as if they are doing zone transfers across a dial on demand dialup link, which can be brought up by traffic originating from this server. This has different effects according to zone type and concentrates the zone maintenance so that it all happens in a short interval, once every
+heartbeat-interval
+ and hopefully during the one call. It also suppresses some of the normal zone maintenance traffic. The default is
+no
+.
+
+
+
+The
+dialup
+ option may also be specified in the
+zone
+ statement, in which case it overrides the
+options dialup
+statement.
+
+
+
+If the zone is a
+master
+ then the server will send out a NOTIFY request to all the slaves. This will trigger the zone serial number check in the slave (providing it supports NOTIFY) allowing the
+slave
+ to verify the zone while the connection is active.
+
+
+
+If the zone is a
+slave
+ or
+stub
+ then the server will suppress the regular "zone up to date" queries and only perform them when the
+
+heartbeat-interval
+ expires.
+
+
+If
+yes
+ (the default), the server will fetch "glue" resource records it doesn't have when constructing the additional data section of a response. (Information present outside of the authoritative nodes in the zone is called "glue" information).
+fetch-glue
+
+no
+ can be used in conjunction with
+recursion no
+to prevent the server's cache from growing or becoming corrupted (at the cost of requiring more work from the client).
+
+
+Setting the option to
+yes
+ is equivalent to setting the following three options:
+auth-nxdomain yes
+;,
+maintain-ixfr-base yes
+; and
+ rfc2308-type1 no
+;. The use of
+has-old-clients
+ with
+auth-nxdomain
+,
+maintain-ixfr-base
+ and
+rfc2308-type1
+ is order dependent. The default is
+no
+.
+
+
+
+(Note that this is a broken implementation iin BIND version 8. It should not be necessary in any but the oldest of BIND installations.)
+
+
+If
+yes
+, then statistics are kept for every host that the nameserver interacts with. The default is
+no
+. Note: turning on
+host-statistics
+ can consume huge amounts of memory.
+
+
+If
+yes
+, then multiple CNAME resource records will be allowed for a domain name. The default is
+no
+. Allowing multiple CNAME records is against standards and is not recommended. Multiple CNAME support is available because previous versions of BIND allowed multiple CNAME records, and these records have been used for load balancing by a number of sites.
+
+
+If
+yes
+ (the default), DNS NOTIFY messages are sent when a zone the server is authoritative for changes. The use of NOTIFY speeds synchronization between the master and its slaves. Slave servers that receive a NOTIFY message and understand it will contact the master server for the zone and see if they need to do a zone transfer, and if they do, they will initiate it immediately. The
+notify
+ option may also be specified in the
+zone
+ statement, in which case it overrides the
+options notify
+ statement. It would only be necessary to turn off this option if it caused slaves to crash.
+
+
+If
+yes
+, and a DNS query requests recursion, then the server will attempt to do all the work required to answer the query. If recursion is not on, the server will return a referral to the client if it doesn't know the answer. The default is
+yes
+. See also
+fetch-glue
+ above.
+
+
+If
+yes
+, the server will send NS records along with the SOA record for negative answers. You need to set this to
+no
+ if you have an old BIND server using you as a forwarder that does not understand negative answers which contain both SOA and NS records or you have an old version of sendmail. The correct fix is to upgrade the broken server or sendmail. The default is
+no
+.
+
+
+If
+yes
+, the server will treat `
+\r
+' characters the same way it treats a
+<space>
+"
+
+" or `
+\t
+'. This may be necessary when loading zone files on a UNIX system that were generated on an NT or DOS machine. The default is
+no
+.
+
+
+The forwarding facility can be used to create a large site-wide cache on a few servers, reducing traffic over links to external nameservers. It can also be used to allow queries by servers that do not have direct access to the Internet, but wish to look up exterior names anyway. Forwarding occurs only on those queries for which the server is not authoritative and does not have the answer in its cache.
+
+
+This option is only meaningful if the forwarders list is not empty. A value of
+first
+, the default, causes the server to query the forwarders first, and if that doesn't answer the question the server will then look for the answer itself. If
+only
+ is specified, the server will only query the forwarders.
+
+
+Specifies the IP addresses to be used for forwarding. The default is the empty list (no forwarding).
+
+
+
+
+
+
+Forwarding can also be configured on a per-zone basis, allowing for the global forwarding options to be overridden in a variety of ways. You can set particular zones to use different forwarders, or have different
+forward only/first behavior
+, or not forward at all. See
+zone Statement Grammar
+ for more information.
+
+
+
+Future versions of BIND will continue to support the forward and forwarders options syntax.
+
+
+The server can check domain names based upon their expected client contexts. For example, a domain name used as a hostname can be checked for compliance with the RFCs defining valid hostnames.
+
+
+Names are checked against their expected client contexts. Invalid names are logged, and the offending data is rejected.
+
+
+
+
+
+
+The server can check names in three areas: master zone files, slave zone files, and in responses to queries the server has initiated. If
+check-names response fail
+ has been specified, and answering the client's question would require sending an invalid name to the client, the server will send a REFUSED response code to the client.
+
+
+
+check-names
+ may also be specified in the
+zone
+ statement, in which case it overrides the
+options check-names
+ statement. When used in a
+zone
+ statement, the area is not specified (because it can be deduced from the zone type).
+
+
+Access to the server can be restricted based on the IP address of the requesting system. See
+Address Match Lists
+ for details on how to specify IP address lists.
+
+
+Specifies which hosts are allowed to ask ordinary questions.
+allow-query
+ may also be specified in the
+zone
+ statement, in which case it overrides the
+options allow-query
+ statement. If not specified, the default is to allow queries from all hosts.
+
+
+Specifies which hosts are allowed to make recursive queries through this server. If not specified, the default is to allow recursive queries from all hosts.
+
+
+Specifies which hosts are allowed to receive zone transfers from the server.
+allow-transfer
+ may also be specified in the
+zone
+ statement, in which case it overrides the
+options allow-transfer
+ statement. If not specified, the default is to allow transfers from all hosts.
+
+
+Specifies a list of addresses that the server will not accept queries from or use to resolve a query. Queries from these addresses will not be responded to. The default is
+none
+.
+
+
+The interfaces and ports that the server will answer queries from may be specified using the
+listen-on
+ option.
+listen-on
+ takes an optional port, and an
+address_match_list
+. The server will listen on all interfaces allowed by the address match list. If a port is not specified, port 53 will be used.
+
+
+
+Multiple listen-on statements are allowed. For example,
+
+
+If the server doesn't know the answer to a question, it will query other nameservers.
+query-source
+ specifies the address and port used for such queries. If
+address
+ is
+*
+ or is omitted, a wildcard IP address (
+INADDR_ANY
+) will be used. If
+port
+ is
+*
+ or is omitted, a random unprivileged port will be used. The default is
+
+query-source address * port *;
+
+
+
+Note:
+query-source
+ currently applies only to UDP queries; TCP queries always use a wildcard IP address and a random unprivileged port.
+
+
+BIND has mechanisms in place to facilitate zone transfers and set limits on the amount of load that transfers place on the system. The following options apply to zone transfers.
+
+
+The server supports two zone transfer methods.
+one-answer
+ uses one DNS message per resource record transferred.
+many-answers
+ packs as many resource records as possible into a message.
+many-answers
+ is more efficient, but is only known to be understood by BIND 8.x and patched versions of BIND 4.9.5. The default is
+one-answer
+.
+transfer-format
+ may be overridden on a per-server basis by using the
+server
+ statement.
+
+
+The maximum number of inbound zone transfers that can be running concurrently. The default value is 10. Increasing
+transfers-in
+ may speed up the convergence of slave zones, but it also may increase the load on the local system.
+
+
+This option will be used in the future to limit the number of concurrent outbound zone transfers. It is checked for syntax, but is otherwise ignored.
+
+
+The maximum number of inbound zone transfers (
+named-xfer
+processes) that can be concurrently transferring from a given remote nameserver. The default value is 2. Increasing
+transfers-per-ns
+ may speed up the convergence of slave zones, but it also may increase the load on the remote nameserver.
+transfers-per-ns
+ may be overridden on a per-server basis by using the
+transfers
+ phrase of the
+server
+ statement.
+
+
+
+transfer-source
+ determines which local address will be bound to the TCP connection used to fetch all zones transferred inbound by the server. If not set, it defaults to a system controlled value which will usually be the address of the interface "closest to" the remote end. This address must appear in the remote end's
+allow-transfer
+ option for the zone being transferred, if one is specified. This statement sets the
+transfer-source
+ for all zones, but can be overridden on a per-zone basis by including a
+
+transfer-source
+ statement within the
+zone
+ block in the configuration file.
+
+
+Slave servers will periodically query master servers to find out if zone serial numbers have changed. Each such query uses a minute amount of the slave server's network bandwidth, but more importantly each query uses a small amount of memory in the slave server while waiting for the master server to respond. The
+serial-queries
+option sets the maximum number of concurrent serial-number queries allowed to be outstanding at any given time. The default is 4. Note: If a server loads a large (tens or hundreds of thousands) number of slave zones, then this limit should be raised to the high hundreds or low thousands -- otherwise the slave server may never actually become aware of zone changes in the master servers. Beware, though, that setting this limit arbitrarily high can spend a considerable amount of your slave server's network, CPU, and memory resources. As with all tunable limits, this one should be changed gently and monitored for its effects.
+
+
+Defines a global list of IP addresses that are also sent NOTIFY messages whenever a fresh copy of the zone is loaded. This helps to ensure that copies of the zones will quickly converge on "stealth" servers. If an
+also-notify
+ list is given in a
+zone
+ statement, it will override the
+options also-notify
+ statement. When a
+zone notify
+ statement is set to
+no
+, the IP addresses in the global
+also-notify
+ list will not be sent NOTIFY messages for that zone. The default is the empty list (no global notification list).
+
+
+The server's usage of many system resources can be limited. Some operating systems don't support some of the limits. On such systems, a warning will be issued if the unsupported limit is used. Some operating systems don't support limiting resources, and on these systems a
+cannot set resource limits on this system
+ message will be logged.
+
+
+
+Scaled values are allowed when specifying resource limits. For example,
+1G
+ can be used instead of
+1073741824
+ to specify a limit of one gigabyte.
+unlimited
+ requests unlimited use, or the maximum available amount.
+default
+ uses the limit that was in force when the server was started. See the description of
+size_spec
+ in
+Configuration File Grammar
+ for more details.
+
+
+The maximum number of files the server may have open concurrently. The default is
+unlimited
+. Note: on some operating systems the server cannot set an unlimited value and cannot determine the maximum number of open files the kernel can support. On such systems, choosing
+unlimited
+ will cause the server to use the larger of the
+rlim_max
+ for
+RLIMIT_NOFILE
+ and the value returned by
+sysconf(_SC_OPEN_MAX)
+. If the actual kernel limit is larger than this value, use
+limit files
+to specify the limit explicitly.
+
+
+The
+max-ixfr-log-size
+ will be used in a future release of the server to limit the size of the transaction log kept for Incremental Zone Transfer.
+
+
+The server will remove expired resource records from the cache every
+cleaning-interval
+minutes. The default is 60 minutes. If set to 0, no periodic cleaning will occur.
+
+
+The server will perform zone maintenance tasks for all zones marked
+dialup yes
+ whenever this interval expires. The default is 60 minutes. Reasonable values are up to 1 day (1440 minutes). If set to 0, no zone maintenance for these zones will occur.
+
+
+The server will scan the network interface list every
+interface-interval
+ minutes. The default is 60 minutes. If set to 0, interface scanning will only occur when the configuration file is loaded. After the scan, listeners will be started on any new interfaces (provided they are allowed by the
+listen-on
+ configuration). Listeners on interfaces that have gone away will be cleaned up.
+
+
+All other things being equal, when the server chooses a nameserver to query from a list of nameservers, it prefers the one that is topologically closest to itself. The
+topology
+ statement takes an
+address_match_list
+ and interprets it in a special way. Each top-level list element is assigned a distance. Non-negated elements get a distance based on their position in the list, where the closer the match is to the start of the list, the shorter the distance is between it and the server. A negated match will be assigned the maximum distance from the server. If there is no match, the address will get a distance which is further than any non-negated list element, and closer than any negated element. For example,
+
+
+will prefer servers on network 10 the most, followed by hosts on network 1.2.0.0 (netmask 255.255.0.0) and network 3, with the exception of hosts on network 1.2.3 (netmask 255.255.255.0), which is preferred least of all.
+
+
+Resource Records (RRs) are the data associated with the names in a domain name space. The data is maintained in the form of sets of RRs. The order of RRs in a set is, by default, not significant. Therefore, to control the sorting of records in a set resource records, or
+RRset
+, you must use the
+sortlist
+ statement.
+
+
+When returning multiple RRs, the nameserver will normally return them in
+Round Robin
+ order, i.e. after each request, the first RR is put at the end of the list. The client resolver code should rearrange the RRs as appropriate, i.e. using any addresses on the local net in preference to other addresses. However, not all resolvers can do this or are correctly configured. When a client is using a local server the sorting can be performed in the server, based on the client's address. This only requires configuring the nameservers, not all the clients.
+
+
+
+The
+sortlist
+ statement (see below) takes an
+address_match_list
+and interprets it even more specifically than the
+topology
+ statement does (see
+Topology
+). Each top level statement in the
+sortlist
+ must itself be an explicit
+address_match_list
+ with one or two elements. The first element (which may be an IP address, an IP prefix, an ACL name or a nested
+address_match_list
+) of each top level list is checked against the source address of the query until a match is found.
+
+
+
+Once the source address of the query has been matched, if the top level statement contains only one element, the actual primitive element that matched the source address is used to select the address in the response to move to the beginning of the response. If the statement is a list of two elements, then the second element is treated like the
+address_match_list
+ in a
+topology
+ statement. Each top level element is assigned a distance and the address in the response with the minimum distance is moved to the beginning of the response.
+
+
+
+In the following example, any queries received from any of the addresses of the host itself will get responses preferring addresses on any of the locally connected networks. Next most preferred are addresses on the 192.168.1/24 network, and after that either the 192.168.2/24 or
+192.168.3/24 network with no preference shown between these two networks. Queries received from a host on the 192.168.1/24 network will prefer other addresses on that network to the 192.168.2/24 and
+192.168.3/24 networks. Queries received from a host on the 192.168.4/24 or the 192.168.5/24 network will only prefer other addresses on their directly connected networks.
+
+sortlist {
+ { localhost; // IF the local host
+ { localnets; // THEN first fit on the
+ 192.168.1/24; // following nets
+ { 192,168.2/24; 192.168.3/24; }; }; };
+ { 192.168.1/24; // IF on class C 192.168.1
+ { 192.168.1/24; // THEN use .1, or .2 or .3
+ { 192.168.2/24; 192.168.3/24; }; }; };
+ { 192.168.2/24; // IF on class C 192.168.2
+ { 192.168.2/24; // THEN use .2, or .1 or .3
+ { 192.168.1/24; 192.168.3/24; }; }; };
+ { 192.168.3/24; // IF on class C 192.168.3
+ { 192.168.3/24; // THEN use .3, or .1 or .2
+ { 192.168.1/24; 192.168.2/24; }; }; };
+ { { 192.168.4/24; 192.168.5/24; };
+ // if .4 or .5, prefer that net
+ };
+};
+
+
+
+The following example will give reasonable behavior for the local host and hosts on directly connected networks. It is similar to the behavior of the address sort in BIND 8.x. Responses sent to queries from the local host will favor any of the directly connected networks. Responses sent to queries from any other hosts on a directly connected network will prefer addresses on that same network. Responses to other queries will not be sorted.
+
+
+When multiple records are returned in an answer it may be useful to configure the order of the records placed into the response. For example, the records for a zone might be configured always to be returned in the order they are defined in the zone file. Or perhaps a random shuffle of the records as they are returned is wanted. The
+rrset-order
+ statement permits configuration of the ordering made of the records in a multiple record response. The default, if no ordering is defined, is a cyclic ordering (round robin).
+ rrset-order {
+ class IN type A name "host.example.com" order random;
+ order cyclic;
+ };
+
+
+
+will cause any responses for type
+A
+ records in class
+IN
+ that have "host.example.com" as a suffix, to always be returned in random order. All other records are returned in cyclic order.
+
+
+
+If multiple
+rrset-order
+ statements appear, they are not combined--the last one applies.
+
+
+
+If no
+rrset-order
+ statement is specified, then a default one of:
+
+ rrset-order { class ANY type ANY name "*"; order cyclic ; };
+
+
+Sets the number of seconds to cache a lame server indication. 0 disables caching. (This is NOT recommended.) Default is 600 (10 minutes). Maximum value is 1800 (30 minutes).
+
+
+To reduce network traffic and increase performance the server stores negative answers.
+max-ncache-ttl
+ is used to set a maximum retention time for these answers in the server in seconds. The default
+
+max-ncache-ttl
+ is 10800 seconds (3 hours).
+
+max-ncache-ttl
+ cannot exceed the maximum retention time for ordinary (positive) answers (7 days) and will be silently truncated to 7 days if set to a value which is greater that 7 days.
+
+
+
+use-ixfr
+ is deprecated in BINDv9. If you need to disable IXFR to a particular server or servers see information on the
+support-ixfr
+ option in the Server Statement description (
+server Statement Grammar
+ , below) and in the description of Incremental Transfer (IXFR) (
+Incremental Transfer (IXFR)
+).
+
+
+5.2.14
+server
+ Statement Definition and Usage
+
+
+
+
+The server statement defines the characteristics to be associated with a remote nameserver.
+
+
+
+If you discover that a remote server is giving out bad data, marking it as bogus will prevent further queries to it. The default value of
+bogus
+ is
+no
+.
+
+
+
+The server supports two zone transfer methods. The first,
+one-answer
+, uses one DNS message per resource record transferred.
+many-answers
+ packs as many resource records as possible into a message.
+many-answers
+ is more efficient, but is only known to be understood by BIND 8.2 and patched versions of BIND 4.9.5. You can specify which method to use for a server with the
+transfer-format
+option. If
+transfer-format
+is not specified, the
+transfer-format
+ specified by the
+options
+ statement will be used.
+
+
+
+
+transfers
+ is used to limit the number of concurrent in-bound zone transfers from the specified server.
+
+
+
+The
+keys
+ clause is used to identify a
+key_id
+defined by the
+key
+ statement, to be used for transaction security when talking to the remote server. The
+key
+ statement must come before the
+server
+ statement that references it. When a request is sent to the remote server, a request signature will be generated using the key specified here and appended to the message. A request originating from the remote server is not required to be signed by this key.
+trusted-keys {
+ string number number number string
+ ;
+ [string number number number string
+ ; [...]]
+};
+
+
+
+
+
+
+5.2.16
+trusted-keys
+ Statement Definition and Usage
+
+
+
+
+The trusted-keys statement is for use with DNSSEC-style security, originally specified in RFC 2065. DNSSEC is meant to provide three distinct services: key distribution, data origin authentication, and transaction and request authentication. A complete description of DNSSEC and its use is beyond the scope of this document, and readers interested in more information should start with RFC 2065 and then continue with the relevant
+Internet Drafts
+ (IDs) documents. A list of the Internet Drafts pertaining to DNSSEC can be found in
+Internet Drafts
+ in Appendix C of this document. (Their filenames begin with "draft-ietf-dnssec."). IDs are RFCs in their preliminary stages of development--they are the working drafts of IETF working groups--and can be obtained via anonymous
+FTP
+ from
+
+ftp://www.isi.edu/internet-drafts/ or ftp://www.ietf.org/rfcs/
+.
+
+
+
+Each trusted key is associated with a domain name. Its attributes are the non-negative integral flags, protocol, and algorithm, as well as a base-64 encoded string representing the key.
+
+
+
+A trusted key is added when a public key for a non-authoritative zone is known, but cannot be securely obtained through DNS. This occurs when a signed zone is a child of an unsigned zone. Adding the trusted key here allows data signed by that zone to be considered secure.
+
+
+All log output goes to one or more "channels"; you can make as many of them as you want.
+
+
+
+Every
+channel
+ definition must include a clause that says whether messages selected for the channel go to a file, to a particular syslog facility, or are discarded. It can optionally also limit the message severity level that will be accepted by the channel (default is
+info
+), and whether to include a
+named
+-generated time stamp, the category name and/or severity level (default is not to include any).
+
+
+
+The word
+null
+ as the destination option for the channel will cause all messages sent to it to be discarded; in that case, other options for the channel are meaningless.
+
+
+
+The
+file
+ clause can include limitations both on how large the file is allowed to become, and how many versions of the file will be saved each time the file is opened.
+
+
+
+The
+size
+ option for files is simply a hard ceiling on log growth. If the file ever exceeds the size, then
+named
+ will not write anything more to it until the file is reopened; exceeding the size does not automatically trigger a reopen. The default behavior is not to limit the size of the file.
+
+
+
+If you use the
+version
+ log file option, then
+named
+ will retain that many backup versions of the file by renaming them when opening. For example, if you choose to keep 3 old versions of the file
+lamers.log
+ then just before it is opened
+lamers.log.1
+ is renamed to
+lames.log.2
+,
+lamers.log.0
+ is renamed to
+lamers.log.1
+, and
+lamers.log
+ is renamed to
+lamers.log.0
+. No rolled versions are kept by default; any existing log file is simply appended. The
+unlimited
+ keyword is synonymous with
+99
+ in current BIND releases.
+
+
+
+Example usage of the size and versions options:
+
+
+The argument for the
+syslog
+ clause is a syslog facility as described in the
+syslog
+ manual page. How
+syslog
+ will handle messages sent to this facility is described in the
+syslog.conf
+ manual page. If you have a system which uses a very old version of
+syslog
+ that only uses two arguments to the
+openlog()
+ function, then this clause is silently ignored.
+
+
+
+The
+severity
+ clause works like
+syslog
+'s "priorities," except that they can also be used if you are writing straight to a file rather than using
+syslog
+. Messages which are not at least of the severity level given will not be selected for the channel; messages of higher severity levels will be accepted.
+
+
+
+If you are using
+syslog
+, then the
+syslog.conf
+ priorities will also determine what eventually passes through. For example, defining a channel facility and severity as
+daemon
+ and
+debug
+ but only logging
+daemon.warning
+ via
+syslog.conf
+ will cause messages of severity
+info
+ and
+notice
+ to be dropped. If the situation were reversed, with
+named
+ writing messages of only
+warning
+ or higher, then
+syslogd
+ would print all messages it received from the channel.
+
+
+
+The server can supply extensive debugging information when it is in debugging mode. If the server's global debug level is greater than zero, then debugging mode will be active. The global debug level is set either by starting the
+named
+ server with the "-d" flag followed by a positive integer, or by running "ndc trace". The global debug level can be set to zero, and debugging mode turned off, by running "ndc notrace". All debugging messages in the server have a debug level, and higher debug levels give more detailed output. Channels that specify a specific debug severity, e.g.
+
+
+will get debugging output of level 3 or less any time the server is in debugging mode, regardless of the global debugging level. Channels with
+dynamic
+ severity use the server's global level to determine what messages to print.
+
+
+
+If
+print-time
+ has been turned on, then the date and time will be logged.
+print-time
+ may be specified for a
+syslog
+ channel, but is usually pointless since
+syslog
+ also prints the date and time. If
+print-category
+ is requested, then the category of the message will be logged as well. Finally, if
+print-severity
+ is on, then the severity level of the message will be logged. The
+print-
+ options may be used in any combination, and will always be printed in the following order: time, category, severity. Here is an example where all three
+print-
+ options are on:
+
+
+
+28-Apr-1997 15:05:32.863 default: notice: Ready to answer queries.
+
+
+
+There are four predefined channels that are used for
+named
+'s default logging as follows. How they are used is described in the section
+The category Phrase
+.
+
+ channel default_syslog {
+ syslog daemon; # send to syslog's daemon facility
+ severity info; # only send priority info and higher
+ };
+ channel default_debug {
+ file "named.run"; # write to named.run in the working directory
+ # Note: stderr is used instead of "named.run"
+ # if the server is started with the "-f"
+ # option.
+ severity dynamic # log at the server's current debug level
+ };
+ channel default_stderr { # writes to stderr
+ file "<stderr>"; # this is illustrative only;
+ # there's currently no way of
+ # specifying an internal file
+ # descriptor in the configuration
+ # language.
+ severity info; # only send priority info and higher
+ };
+ channel null {
+ null; # toss anything sent to this channel
+ };
+
+
+
+Once a channel is defined, it cannot be redefined. Thus you cannot alter the built-in channels directly, but you can modify the default logging by pointing categories at channels you have defined.
+
+
+There are many categories, so you can send the logs you want to see wherever you want, without seeing logs you don't want. If you don't specify a list of channels for a category, then log messages in that category will be sent to the
+default
+ category instead. If you don't specify a default category, the following "default default" is used:
+
+
+As an example, let's say you want to log security events to a file, but you also want keep the default logging behavior. You'd specify the following:
+
+
+The catch-all. Many things still aren't classified into categories, and they all end up here. Also, if you don't specify any channels for a category, the default category is used instead. If you do not define the default category, the following definition is used:
+
+category default { default_syslog; default_debug; };
+
+
+
+If the server has to shut itself down due to an internal problem, it will log the problem in this category as well as in the problem's native category. If you do not define the panic category, the following definition is used:
+
+category panic { default_syslog; default_stderr; };
+
+
+
+Debugging info from the event system. Only one channel may be specified for this category, and it must be a file channel. If you do not define the eventlib category, the following definition is used:
+
+category eventlib{ default_debug; };
+
+
+
+Dumps of packets received and sent. Only one channel may be specified for this category, and it must be a file channel. If you do not define the packet category, the following definition is used:
+
+category packet { default_debug; };
+
+
+
+Messages arising from response checking, such as "Malformed response...", "wrong ans. name...", "unrelated additional info...", "invalid RR type...", and "bad referral...".
+
+
+5.2.18
+view
+ Statement Definition and Usage
+
+
+
+
+
+view
+ statements are used to provide a different view of the same namespace to different clients, depending upon which
+allow-query
+ statement they match. A
+view
+ statement with no
+allow-query
+ statement is the default view, for any client that does not match a specific view. The
+view
+ statement should contain a list of zone definitions for each zone that needs differing answers. Zones that are specified outside the
+view
+ statement are common to all views.
+
+
+
+
+
+
+A slave zone is a replica of a master zone. The masters list specifies one or more IP addresses that the slave contacts to update its copy of the zone. If a port is specified, the slave then checks to see if the zone is current and zone transfers will be done to the port given. If a file is specified, then the replica will be written to this file whenever the zone is changed, and reloaded from this file on a server restart. Use of a file is recommended, since it often speeds server start-up and eliminates a needless waste of bandwidth. Note that for large numbers (in the tens or hundreds of thousands) of zones per server, it is best to use a two level naming scheme for zone file names. For example, a slave server for the zone
+example.com
+ might place the zone contents into a file called
+
+ex/example.com
+ where
+ex/
+ is just the first two letters of the zone name. (Most operating systems behave very slowly if you put 100K files into a single directory.)
+
+
+A forward zone is used to direct all queries in it to other servers.
+
+
+
+The specification of options in such a zone will override any global options declared in the options statement.
+
+
+
+If no
+forwarders
+ statement is present in the zone or an empty list for
+forwarders
+ is given, then no forwarding will be done for the zone, cancelling the effects of any forwarders in the
+options
+ statement. Thus if you want to use this type of zone to change the behavior of the global
+forward
+ option (i.e., "forward first to, " then "forward only," or vice versa, but want to use the same servers as set globally) you need to respecify the global forwarders.
+
+
+The initial set of root nameservers is specified using a hint zone. When the server starts up, it uses the root hints to find a root nameserver and get the most recent list of root nameservers.
+
+
+The zone's name may optionally be followed by a class. If a class is not specified, class
+in
+ (for
+internet
+), is assumed. This is correct for the vast majority of cases.
+
+
+
+The
+hesiod
+class is for an information service from MIT's Project Athena. It is used to share information about various systems databases, such as users, groups, printers and so on. The keyword
+hs
+ is a synonym for hesiod.
+
+
+
+Another MIT development was CHAOSnet, a LAN protocol created in the mid-1970s. Zone data for it can be specified with the
+chaos
+ class.
+
+
+Only meaningful if
+notify
+ is active for this zone. The set of machines that will receive a
+DNS NOTIFY
+ message for this zone is made up of all the listed nameservers for the zone (other than the primary master) plus any IP addresses specified with
+also-notify
+.
+
+also-notify
+ is not meaningful for stub zones. The default is the empty list.
+
+
+Only meaningful if the zone has a forwarders list. The
+only
+ value causes the lookup to fail after trying the forwarders and getting no answer, while
+first
+ would allow a normal lookup to be tried.
+
+
+Used to override the list of global forwarders. If it is not specified in a zone of type
+forward
+, no forwarding is done for the zone; the global options are not used.
+
+
+Represents a public key for this zone. It is needed when this is the top level authoritative zone served by this server and there is no chain of trust to a trusted key. It is considered secure, so that data that it signs will be considered secure. The DNSSEC flags, protocol, and algorithm are specified, as well as a base-64 encoded string representing the key.
+
+
+Determines which local address will be bound to the TCP connection used to fetch this zone. If not set, it defaults to a system controlled value which will usually be the address of the interface
+closest to
+ the remote end. This address must appear in the remote end's
+allow-transfer
+ option for this zone if one is specified.
+
+
+5.3.1
+
+Types of Resource Records and When to Use Them
+
+
+
+
+This section, largely borrowed from RFC 1034, describes the concept of a Resource Record (RR) and explains when each is used. Since the publication of RFC 1034, several new RRs have been identified and implemented in the DNS. These are also included.
+
+
+A domain name identifies a node. Each node has a set of resource information, which may be empty. The set of resource information associated with a particular name is composed of separate RRs. The order of RRs in a set is not significant and need not be preserved by nameservers, resolvers, or other parts of the DNS. However, sorting of multiple RRs is permitted for optimization purposes, for example, to specify that a particular nearby server be tried first. See
+The sortlist Statement
+ and
+RRset Ordering
+ for details.
+
+
+the time to live of the RR. This field is a 32 bit integer in units of seconds, and is primarily used by resolvers when they cache RRs. The TTL describes how long a RR can be cached before it should be discarded.
+
+
+the type and sometimes class-dependent data that describes the resource.
+
+
+
+
+
+
+The following are
+types
+ of valid RRs (some of these listed, although not obsolete, are experimental (x) or historical (h) and no longer in general use):
+
+
+used in DNSSEC to securely indicate that RRs with an owner name in a certain name interval do not exist in a zone and indicate what RR types are present for an existing name. See RFC 2535 for details.
+
+
+provides alternate naming to an entire subtree of the domain name space, rather than to a single node. It causes some suffix of a queried name to be substituted with a name from the DNAME record's RDATA.
+
+
+The owner name is often implicit, rather than forming an integral part of the RR. For example, many nameservers internally form tree or hash structures for the name space, and chain RRs off nodes. The remaining RR parts are the fixed header (type, class, TTL) which is consistent for all RRs, and a variable part (RDATA) that fits the needs of the resource being described.
+
+
+
+The meaning of the TTL field is a time limit on how long an RR can be kept in a cache. This limit does not apply to authoritative data in zones; it is also timed out, but by the refreshing policies for the zone. The TTL is assigned by the administrator for the zone where the data originates. While short TTLs can be used to minimize caching, and a zero TTL prohibits caching, the realities of Internet performance suggest that these times should be on the order of days for the typical host. If a change can be anticipated, the TTL can be reduced prior to the change to minimize inconsistency during the change, and then increased back to its former value following the change.
+
+
+
+The data in the RDATA section of RRs is carried as a combination of binary strings and domain names. The domain names are frequently used as "pointers" to other data in the DNS.
+
+
+RRs are represented in binary form in the packets of the DNS protocol, and are usually represented in highly encoded form when stored in a nameserver or resolver. In the examples provided in RFC 1034, a style similar to that used in master files was employed in order to show the contents of RRs. In this format, most RRs are shown on a single line, although continuation lines are possible using parentheses.
+
+
+
+The start of the line gives the owner of the RR. If a line begins with a blank, then the owner is assumed to be the same as that of the previous RR. Blank lines are often included for readability.
+
+
+
+Following the owner, we list the TTL, type, and class of the RR. Class and type use the mnemonics defined above, and TTL is an integer before the type field. In order to avoid ambiguity in parsing, type and class mnemonics are disjoint, TTLs are integers, and the type mnemonic is always last. The IN class and TTL values are often omitted from examples in the interests of clarity.
+
+
+
+The resource data or RDATA section of the RR are given using knowledge of the typical representation for the data.
+
+
+
+For example, we might show the RRs carried in a message as:
+
+
+The MX RRs have an RDATA section which consists of a 16 bit number followed by a domain name. The address RRs use a standard IP address format to contain a 32 bit internet address.
+
+
+
+This example shows six RRs, with two RRs at each of three domain names.
+
+
+As described above, domain servers store information as a series of resource records, each of which contains a particular piece of information about a given domain name (which is usually, but not always, a host). The simplest way to think of a RR is as a typed pair of datum, a domain name matched with relevant data, and stored with some additional type information to help systems determine when the RR is relevant.
+
+
+
+MX records are used to control delivery of email. The data specified in the record is a priority and a domain name. The priority controls the order in which email delivery is attempted, with the lowest number first. If two priorities are the same, a server is chosen randomly. If no servers at a given priority are responding, the mail transport agent will fall back to the next largest priority. Priority numbers do not have any absolute meaning - they are relevant only respective to other MX records for that domain name. The domain name given is the machine to which the mail will be delivered. It
+must
+ have an associated A record--a CNAME is not sufficient.
+
+
+
+For a given domain, if there is both a CNAME record and an MX record, the MX record is in error, and will be ignored. Instead, the mail will be delivered to the server specified in the MX record pointed to by the CNAME.
+
+
+Mail delivery will be attempted to mail.foo.com and mail2.foo.com (in any order), and if neither of those succeed, delivery to mail.backup.org will be attempted.
+
+
+The time to live of the RR field is a 32 bit integer represented in units of seconds, and is primarily used by resolvers when they cache RRs. The TTL describes how long a RR can be cached before it should be discarded. The following three types of TTL are currently used in a zone file.
+
+
+The last field in the SOA is the negative caching TTL. This controls how long other servers will cache no-such-domain (NXDOMAIN) responses from you.
+
+
+
+The maximum time for negative caching is 3 hours (3h).
+
+
+Reverse name resolution (i.e., translation from IP address to name) is achieved by means of the in-addr.arpa domain and PTR records. Entries in the in-addr.arpa domain are made in least-to-most significant order, read left to right. This is the opposite order to the way IP addresses are usually written. Thus, a machine with an IP address of 10.1.2.3 would have a corresponding in-addr.arpa name of
+3.2.1.10.in-addr.arpa. This name should have a PTR resource record whose data field is the name of the machine or, optionally, multiple PTR records if the machine has more than one name. For example, in the
+example.com
+ domain:
+
+$ORIGIN 2.1.10.in-addr.arpa
+3 IN PTR foo.example.com.
+
+
+
+(Note: The $ORIGIN lines in the examples are for providing context to the examples only--they do not necessarily appear in the actual usage. They are only used here to indicate that the example is relative to the listed $ORIGIN.)
+
+
+The Master File Format was initially defined in RFC 1035 and has subsequently been extended. While the Master File Format itself is class independent all records in a Master File must be of the same class.
+
+
+
+Master File Directives include
+$ORIGIN
+,
+$INCLUDE
+, and
+$TTL.
+
+
+
+
+$ORIGIN
+sets the domain name that will be appended to any unqualified records. When a zone is first read in there is an implicit
+$ORIGIN
+<zone-name>
+.
+ The current
+$ORIGIN
+ is appended to the domain specified in the
+$ORIGIN
+ argument if it is not absolute.
+
+
+Read and process the file
+filename
+ as if it were included into the file at this point. If
+origin
+ is specified the file is processed with
+$ORIGIN
+set to that value, otherwise the current
+$ORIGIN
+ is used.
+
+
+
+
+NOTE
+: The behavior when
+origin
+ is specified differs from that described in RFC 1035. The origin and current domain revert to the values they were prior to the
+$INCLUDE
+ once the file has been read.
+
+
+
+$GENERATE
+ is used to create a series of resource records that only differ from each other by an iterator.
+$GENERATE
+can be used to easily generate the sets of records required to support sub /24 reverse delegations described in RFC 2317: Classless IN-ADDR.ARPA delegation.
+
+
+This can be one of two forms: start-stop or start-stop/step. If the first form is used then step is set to 1. All of start, stop and step must be positive.
+
+
+
+lhs
+ describes the owner name of the resource records to be created. Any single
+$
+ symbols within the
+lhs
+ side are replaced by the iterator value. To get a $ in the output use a double
+$
+, e.g.
+$$
+. If the
+lhs
+ is not absolute, the current
+$ORIGIN
+is appended to the name.
+
+
+The BIND nameserver, named, is controlled by means of signals. The following table describes signals that BIND sends and their effects when sent to the server process using the kill command.
+
+
+Causes the server to read
+named.conf
+ and reload the database. If the server is built with the
+FORCED_RELOAD
+ compile-time option, then
+SIGHUP
+ will also cause the server to check the serial number on all secondary zones. Normally the serial numbers are only checked at the SOA-specified intervals.
+
+
+Access Control Lists (ACLs), are address match lists that you can set up and nickname for future use in
+allow-query
+,
+allow-recursion
+,
+blackhole allow-transfer
+, etc.
+
+
+
+Using ACLs allows you to have finer control over who can access your nameserver, without cluttering up your config files with huge lists of IP addresses.
+
+
+
+It is a
+good idea
+ to use ACLs, and to control access to your server. Limiting access to your server by outside parties can help prevent spoofing and DoS attacks against your server.
+
+
+
+Here is an example of how to properly apply ACLs:
+
+
+
+// Set up an ACL named "bogusnets" that will block RFC1918 space,
+// which is commonly used in spoofing attacks.
+
+
+This allows recursive queries of the server from the outside unless recursion has been previously disabled.
+
+
+
+For more information on how to use ACLs to protect your server, see the
+AUSCERT
+ advisory at
+
+ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-1999.004.dns_dos
+
+
+
+On UNIX servers, it is possible to run BIND in a
+chrooted
+ environment (
+chroot()
+) by specifying the "
+-t
+" option. This can help improve system security by placing BIND in a "sandbox," which will limit the damage done if a server is compromised.
+
+
+
+Another useful feature in the UNIX version of BIND is the ability to run the daemon as a nonprivileged user ( -u <user> ) and in a nonprivileged group ( -g <group> ). We suggest running as a nonpriveleged user when using the
+chroot
+ feature.
+
+
+
+Here is an example command line to load BIND in a
+chroot()
+ sandbox,
+
+/var/named
+, and to run
+named
+
+set_uid
+ and
+set_gid
+ it to user 202 and group 202:
+
+
+In order for a
+chroot()
+ environment to work properly in a particular directory (e.g. var/named), you will need to set up an environment that includes everything BIND needs to run. From BIND's point of view, /var/named is the root of the filesystem. You will need
+/dev/null
+, and any library directories and files that BIND needs to run on your system. Please consult your operating system's instructions if you need help figuring out which library files you need to copy over to the
+chroot()
+ sandbox.
+
+
+
+If you are running an operating system that supports static binaries, you can also compile BIND staticly and avoid the need to copy system libraries over to your
+chroot()
+ sandbox.
+
+
+Prior to running the
+named
+ daemon, use the
+touch
+ utility (to change file access and modification times) or the
+chown
+ utility (to set the user id and/or group id) on files to which you want BIND to write.
+
+
+Since dynamic updates do not have per-RR security, access to the dynamic update facility should be strictly limited. The traditional way to do this has been host-based, but BINDv9 allows tranaction signature (TSIG) signed updates to cryptographically verify the updates.
+
+
+
+
+ (Note: The syntax for this not finalized.)
+
+ns named[111]: Lame server on 'www.foo.com' (in 'foo.com'?): [192.168.0.2].53 'ns2.foo.com'
+
+
+
+This is a harmless error message. It means that the server at 192.168.0.2 (ns2.foo.com) is listed as a nameserver for "foo.com", but it doesn't really know anything about foo.com.
+
+
+
+If this is a zone under your control, check each of the nameservers to ensure that they are configured to answer questions properly.
+
+
+
+If it's a zone out on the Internet, it would be nice to notify the owners of the domain in question so that they can take a look at it. In practice, though, not many people have time to do this.
+ns named[111]: bad referral (other.com !< subdomain.other.com)
+
+
+
+This indicates that your nameserver (ns.foo.com) queried the nameserver for foo2.com to find out how to get to subdomain.foo2.com. foo2.com told your nameserver that subdomain.foo2.com was delegated to some other.foo2.com, so your nameserver queried that.
+
+
+
+someother.foo2.com didn't think that subdomain.foo2.com had been delegated to it, so it referred your server (ns.foo.com) back to the foo2.com nameserver.
+ns named-xfer[111]: [192.168.0.1] not authoritative for foo.com, SOA query got rcode 0, aa 0, ancount 1, aucount 0
+
+
+
+This error usually shows up on a slave server. It indicates that the master server is not answering authoritatively for the zone. This usually happens when the zone is rejected (while named is loading) on the master server. Check the logs on the master server. If ancount -- 0, you may be pointing at the wrong master server for the zone.
+ns named[111]: master zone "foo.com" (IN) rejected due to errors (serial111)
+
+
+
+This indicates that the foo.com zone was rejected because of an error in the zone file. Check the lines above this error -- named will usually tell you what it didn't like and where to find it in the zone file.
+ns named[111]: Zone "foo.com" (file foo.com.db): no NS RRs found at zonetop
+
+
+
+The foo.com.db file is missing NS records at the top of the zone (in the SOA section). Check to make sure they exist and that there is white space (spaces or tabs) in front of them. White spaces matter here.
+ns named[111]: Zone "foo.com" (file foo.com.db): No default TTL set using SOA minimum instead
+
+
+
+You need to add a $TTL to the top of the foo.com.db zone file. See RFC2308, or section 3.2.3, "Setting TTLs" in this document, for information on how to use $TTL.
+
+
+Your nameserver is having problems finding the root nameservers. Check your root hints file to make sure it is not corrupted. Also, make sure that your nameserver can reach the Internet.
+
+
+
+If you are running an internal root nameserver, make sure it's configured properly and is answering queries.
+
+
+This usually indicates that another copy of BIND is already running. Verify that you have killed old copies of the daemon.
+
+
+
+This can also pop up if you originally ran named as "root" and now run it as a regular user. named may have left behind an ndc control socket that is owned by root if it crashed, or was not killed gracefully.
+
+
+
+This means that the regular user wouldn't be able to delete it, so it would think named is still running. The solution is to remove any ndc sockets in /usr/local/etc, or /var/run, etc.
+
+
+7.2.1 It's not working; how can I figure out what's wrong?
+
+
+
+
+The best solution to solving installation and configuration issues is to take preventative measures by setting up logging files beforehand (see the sample configurations in
+Sample Configuration and Logging
+). The log files provide a source of hints and information that can be used to figure out what went wrong and how to fix the problem.
+
+
+
+
+
+
+
+7.3 Incrementing and Changing the Serial Number
+
+
+
+
+Zone serial numbers are just numbers--they aren't date related. A lot of people set them to a number that represents a date, usually of the form YYYYMMDDRR. A number of people have been testing these numbers for Y2K compliance and have set the number to the year 2000 to see if it will work. They then try to restore the old serial number. This will cause problems with BIND, because serial numbers are used to indicate that a zone has been updated. If the serial number on the secondary server is lower than the serial number on the primary, the secondary server will attempt to update its copy of the zone.
+
+
+
+Setting the serial number to a lower number on the primary server than the secondary server means that the secondary will not perform updates to its copy of the zone.
+
+
+
+The solution to this is to add 2147483647 (2^31-1) to the number, reload the zone and make sure all secondaries have updated to the new zone serial number, then reset the number to what you want it to be, and reload the zone again.
+
+
+The Internet Software Consortium (ISC) offers a wide range of support and service agreements for BIND, DHCP and INN servers. Four levels of premium support are available and each level includes support for all ISC programs, significant discounts on products and training, and a recognized priority on bug fixes and non-funded feature requests. In addition, ISC offers a standard support agreement package which includes services ranging from bug fix announcements to remote support. It also includes training in BIND, DHCP or INN.
+
+
+Although the "official" beginning of the Domain Name System occurred in 1984 with the publication of RFC 920, the core of the new system was described in 1983 in RFCs 882 and 883. From 1984 to 1987, the ARPAnet (the precursor to today's Internet) became a testbed of experimentation for developing the new naming/addressing scheme in an rapidly expanding, operational network environment. New RFCs were written and published in 1987 that modified the original documents to incorporate improvements based on the working model. RFC 1034, "Domain Names-Concepts and Facilities," and RFC 1035, "Domain Names-Implementation and Specification" were published and became the standards upon which all DNS implementations are built.
+
+
+
+The first working domain name server, called "Jeeves," was written in 1983-84 by Paul Mockapetris for operation on DEC Tops-20 machines located at the University of Southern California's Information Sciences Institute (USC-ISI) and SRI International's Network Information Center (SRI-NIC). A DNS server for Unix machines, the Berkeley Internet Name Domain (BIND) package, was written soon after by a group of graduate students at the University of California at Berkeley under a grant from the US Defense Advanced Research Projects Administration (DARPA). Versions of BIND through 4.8.3 were maintained by the Computer Systems Research Group (CSRG) at UC Berkeley. Douglas Terry, Mark Painter, David Riggle and Songnian Zhou made up the initial BIND project team. After that, additional work on the software package was done by Ralph Campbell. Kevin Dunlap, a Digital Equipment Corporation employee on loan to the CSRG, worked on BIND for 2 years, from 1985 to 1987. Many other people also contributed to BIND development during that time: Doug Kingston, Craig Partridge, Smoot Carl-Mitchell, Mike Muuss, Jim Bloom and Mike Schwartz. BIND maintenance was subsequently handled by Mike Karels and O. Kure.
+
+
+
+BIND versions 4.9 and 4.9.1 were released by Digital Equipment Corporation (now Compaq Computer Corporation). Paul Vixie, then a DEC employee, became BIND's primary caretaker. Paul was assisted by Phil Almquist, Robert Elz, Alan Barrett, Paul Albitz, Bryan Beecher, Andrew Partan, Andy Cherenson, Tom Limoncelli, Berthold Paffrath, Fuat Baran, Anant Kumar, Art Harkin, Win Treese, Don Lewis, Christophe Wolfhugel, and others.
+
+
+
+BIND Version 4.9.2 was sponsored by Vixie Enterprises. Paul Vixie became BIND's principal architect/programmer.
+
+
+
+BIND versions from 4.9.3 onward have been developed and maintained by the Internet Software Consortium with support being provided by ISC's sponsors. As co-architects/programmers, Bob Halley and Paul Vixie released the first production-ready version of BIND version 8 in May 1997.
+
+
+
+
+BIND development work is made possible today by the sponsorship of several corporations, and by the tireless work efforts of numerous individuals.
+
+
+
+Specification documents for the Internet protocol suite, including the DNS, are published as part of the Request for Comments (RFCs) series of technical notes. The standards themselvers are defined by the Internet Engineering Task Force (IETF) and the Internet Engineering Steering Group (IESG). RFCs can be obtained online via FTP at
+
+ftp://www.isi.edu/in-notes/RFCxxx.txt
+ (where
+xxx
+ is the number of the RFC). RFCs are also available via the Web at
+http://www.ietf.org/rfc/
+.
+
+
+Internet Drafts (IDs) are rough-draft working documents of the Internet Engineering Task Force. They are, in essence, RFCs in the preliminary stages of development. Implementors are cautioned not to regard IDs as archival, and they should not be quoted or cited in any formal documents unless accompanied by the disclaimer that they are "works in progress." IDs have a lifespan of six months after which they are deleted unless updated by their authors.
+
+
+
+
+IDs can be obtained via
+
+FTP
+
+ from
+
+
+ftp://www.isi.edu/internet-drafts/
+
+ or from
+
+ http://www.ietf.org/1id-abstracts.html
+
+.
+
Warning! this draft document is the property of the Internet Software Consortium (ISC) and contains proprietary ISC information. It is being distributed for review purposes ONLY. The information in this document is subject to change. Do not redistribute!
+