Scrub: Do more to avoid fragmentation
Automatically submitted.
@@ -240,6 +240,23 @@ func (r *Request) Scrub(reply *dns.Msg) *dns.Msg {
reply.Compress = false
rl := reply.Len()
if size >= rl {
+ if r.Proto() != "udp" {
+ return reply
+ }
+
+ // Last ditch attempt to avoid fragmentation, if the size is bigger than the v4/v6 UDP fragmentation
+ // limit and sent via UDP compress it (in the hope we go under that limit). Limits taken from NSD:
+ //
+ // .., 1480 (EDNS/IPv4), 1220 (EDNS/IPv6), or the advertized EDNS buffer size if that is
+ // smaller than the EDNS default.
+ // See: https://open.nlnetlabs.nl/pipermail/nsd-users/2011-November/001278.html
+ if rl > 1480 && r.Family() == 1 {
+ reply.Compress = true
+ }
+ if rl > 1220 && r.Family() == 2 {
+ reply.Compress = true
+ }
+
return reply
}
