2018-08-13
ISC
Internet Systems Consortium, Inc.
filter-aaaa.so
8
BIND9

# filter-aaaa.so

filter AAAA in DNS responses when A is present
2018
2019
2020
Internet Systems Consortium, Inc. ("ISC")

          plugin query "filter-aaaa.so"
          { parameters };

## DESCRIPTION

`filter-aaaa.so` is a query plugin module for `named`, enabling `named` to omit some IPv6 addresses when responding to clients.

Until BIND 9.12, this feature was implemented natively in `named` and enabled with the `filter-aaaa` ACL and the `filter-aaaa-on-v4` and `filter-aaaa-on-v6` options. These options are now deprecated in `named.conf`, but can be passed as parameters to the `filter-aaaa.so` plugin, for example:

    plugin query "/usr/local/lib/filter-aaaa.so" {
            filter-aaaa-on-v4 yes;
            filter-aaaa-on-v6 yes;
            filter-aaaa { 192.0.2.1; 2001:db8:2::1; };
    };

This module is intended to aid transition from IPv4 to IPv6 by withholding IPv6 addresses from DNS clients which are not connected to the IPv6 Internet, when the name being looked up has an IPv4 address available. Use of this module is not recommended unless absolutely necessary.

Note: This mechanism can erroneously cause other servers not to give AAAA records to their clients. If a recursing server with both IPv6 and IPv4 network connections queries an authoritative server using this mechanism via IPv4, it will be denied AAAA records even if its client is using IPv6.

## OPTIONS

`filter-aaaa`

  Specifies a list of client addresses for which AAAA filtering is to be applied. The default is `any`.

`filter-aaaa-on-v4`

  If set to `yes`, the DNS client is at an IPv4 address, in `filter-aaaa`, and if the response does not include DNSSEC signatures, then all AAAA records are deleted from the response. This filtering applies to all responses and not only authoritative responses.

  If set to `break-dnssec`, then AAAA records are deleted even when DNSSEC is enabled. As suggested by the name, this causes the response to fail to verify, because the DNSSEC protocol is designed to detect deletions.

  This mechanism can erroneously cause other servers not to give AAAA records to their clients. A recursing server with both IPv6 and IPv4 network connections that queries an authoritative server using this mechanism via IPv4 will be denied AAAA records even if its client is using IPv6.

`filter-aaaa-on-v6`

  Identical to `filter-aaaa-on-v4`, except it filters AAAA responses to queries from IPv6 clients instead of IPv4 clients. To filter all responses, set both options to `yes`.

## SEE ALSO

BIND 9 Administrator Reference Manual.