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- Change default for so-sndbuf to 1m, to mitigate a cross-layer

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issue where the UDP socket send buffers are exhausted waiting
  for ARP/NDP resolution. Thanks to Reflyable for the report.
This commit is contained in:
W.C.A. Wijngaards 2025-05-13 15:04:32 +02:00
parent 9152c914af
commit 03772d10fb
5 changed files with 17 additions and 8 deletions
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5
doc/Changelog
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@ -3,6 +3,11 @@
by adding a log_assert() to safeguard future development.
- Fix #1282: log-destaddr fail on long ipv6 addresses.
13 May 2025: Wouter
- Change default for so-sndbuf to 1m, to mitigate a cross-layer
issue where the UDP socket send buffers are exhausted waiting
for ARP/NDP resolution. Thanks to Reflyable for the report.
12 May 2025: Yorgos
- Merge #1280: Fix auth nsec3 code. Fixes NSEC3 code to not break on
broken auth zones that include unsigned out of zone (above apex)

2
doc/example.conf.in
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@ -117,7 +117,7 @@ server:
# buffer size for UDP port 53 outgoing (SO_SNDBUF socket option).
# 0 is system default. Use 4m to handle spikes on very busy servers.
# so-sndbuf: 0
# so-sndbuf: 1m
# use SO_REUSEPORT to distribute queries over threads.
# at extreme load it could be better to turn it off to distribute even.

13
doc/unbound.conf.5.in
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@ -355,11 +355,14 @@ If not 0, then set the SO_SNDBUF socket option to get more buffer space on
UDP port 53 outgoing queries. This for very busy servers handles spikes
in answer traffic, otherwise 'send: resource temporarily unavailable'
can get logged, the buffer overrun is also visible by netstat \-su.
Default is 0 (use system value). Specify the number of bytes to ask
for, try "4m" on a very busy server. The OS caps it at a maximum, on
linux Unbound needs root permission to bypass the limit, or the admin
can use sysctl net.core.wmem_max. On BSD, Solaris changes are similar
to so\-rcvbuf.
Default is 1M. If set to 0 it uses the system value. Specify the number
of bytes to ask for, try "4m" on a very busy server. It needs some space
to be able to deal with packets that wait for local address resolution,
from like ARP and NDP discovery, before they are sent out, hence
it is elevated above the system default by default. The OS caps it at
a maximum, on linux Unbound needs root permission to bypass the limit,
or the admin can use sysctl net.core.wmem_max. On BSD, Solaris changes
are similar to so\-rcvbuf.
.TP
.B so\-reuseport: \fI<yes or no>
If yes, then open dedicated listening sockets for incoming queries for each

3
services/listen_dnsport.c
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@ -473,7 +473,8 @@ create_udp_sock(int family, int socktype, struct sockaddr* addr,
"Got %u. To fix: start with "
"root permissions(linux) or sysctl "
"bigger net.core.wmem_max(linux) or "
"kern.ipc.maxsockbuf(bsd) values.",
"kern.ipc.maxsockbuf(bsd) values. or "
"set so-sndbuf: 0 (use system value).",
(unsigned)snd, (unsigned)got);
}
# ifdef SO_SNDBUFFORCE

2
util/config_file.c
View file

@ -210,7 +210,7 @@ config_create(void)
cfg->if_automatic = 0;
cfg->if_automatic_ports = NULL;
cfg->so_rcvbuf = 0;
cfg->so_sndbuf = 0;
cfg->so_sndbuf = 1024*1024;
cfg->so_reuseport = REUSEPORT_DEFAULT;
cfg->ip_transparent = 0;
cfg->ip_freebind = 0;