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temporarily limit PMTU to 2048, as a workaround to some pathelogical behavior where a TCP stream carried over a UDP peer can throttle down to 0 in the presence of significant packet loss

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Arceliar 2018-02-23 12:46:22 -06:00
parent d3dc7765f2
commit bb3ae8b39b
1 changed files with 9 additions and 0 deletions
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9
src/yggdrasil/session.go
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@ -152,6 +152,15 @@ func (ss *sessions) createSession(theirPermKey *boxPubKey) *sessionInfo {
sinfo.myNonce = *newBoxNonce()
sinfo.theirMTU = 1280
sinfo.myMTU = uint16(ss.core.tun.mtu)
if sinfo.myMTU > 2048 {
// FIXME this is a temporary workaround to an issue with UDP peers
// UDP links need to fragment packets (within ygg) to get them over the wire
// For some reason, TCP streams over UDP peers can get stuck in a bad state
// When this happens, TCP throttles back, and each TCP retransmission loses fragments
// On my wifi network, it seems to happen around the 22nd-23rd fragment of a large packet
// By setting the path MTU to something small, this should (hopefully) mitigate the issue
sinfo.myMTU = 2048
}
higher := false
for idx := range ss.core.boxPub {
if ss.core.boxPub[idx] > sinfo.theirPermPub[idx] {