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Scrub: Do more to avoid fragmentation (#2333)

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This commit is contained in:
Miek Gieben
2018-12-04 20:15:57 +00:00
committed by corbot[bot]
parent b53cc51f53
commit 59a49c5ff7
1 changed files with 17 additions and 0 deletions
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17
request/request.go
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@@ -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
}