- Adjusted so-sndbuf default to 4m.

doc/Changelog

@@ -7,6 +7,7 @@
 	- 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.
+	- Adjusted so-sndbuf default to 4m.
 
 12 May 2025: Yorgos
 	- Merge #1280: Fix auth nsec3 code. Fixes NSEC3 code to not break on

doc/example.conf.in

@@ -116,8 +116,8 @@ server:
 	# so-rcvbuf: 0
 
 	# 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: 1m
+	# 0 is system default. Set larger to handle spikes on very busy servers.
+	# so-sndbuf: 4m
 
 	# use SO_REUSEPORT to distribute queries over threads.
 	# at extreme load it could be better to turn it off to distribute even.

doc/unbound.conf.5.in

@@ -355,8 +355,8 @@ 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 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
+Default is 4m. If set to 0 it uses the system value. Specify the number
+of bytes to ask for, try "8m" 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

util/config_file.c

@@ -210,7 +210,7 @@ config_create(void)
 	cfg->if_automatic = 0;
 	cfg->if_automatic_ports = NULL;
 	cfg->so_rcvbuf = 0;
-	cfg->so_sndbuf = 1024*1024;
+	cfg->so_sndbuf = 4*1024*1024;
 	cfg->so_reuseport = REUSEPORT_DEFAULT;
 	cfg->ip_transparent = 0;
 	cfg->ip_freebind = 0;