2017-09-11 15:41 GMT+03:00 Peter Salin <peter.salin@xxxxxxxxx>: > Hi, > > I encountered some strange PMTUD related behaviour that I need help in > understanding. > > Setup: > > +-----------+ +---+ +--------+ > | 10.0.0.10 |--------| X |--------|10.0.0.3| > +-----------+ +---+ +--------+ > > A one to many socket is setup at 10.0.0.10. Two instances of the lksctp > sctp_darn applications are ran at 10.0.0.3 listening to ports 8001 and 8002. > 10.0.0.3 was also setup to generate ICMP frag needed messages for incoming > messages over 600 bytes. This same issue also occurs also when a router on > the path was setup to generate the ICMP message instead. > > Test 1: > Two associations were connected from 10.0.0.10 to 10.0.0.3, one to port 8001 > and another one to 8002. Then a too large message was sent on the > association to 8001, triggering ICMP generation. When checking the MTU > reported in spinfo_mtu field of SCTP_GET_PEER_ADDR_INFO, the association now > reports 600. The association to 8002 reports 1500 until traffic is sent on > it, at which point it also adjusts to 600 which I think makes sense since > the destination IP is the same. When reopening the associations, the value > of 600 would be remembered for about 10 min, which I also think makes sense > since net.ipv4.route.mtu_expires is 600. > > Test 2: > Again the same two associations were connected to 10.0.0.3, but in addition > an attempt to connect a third association to a non-existing IP was done, > this attempt fails with timeout after a while. After that, again an ICMP > triggering large message was sent to 8001. Now the behaviour is different > from before. The association to 8001 reports a spinfo_mtu of 600, but only > for a brief moment, it does not stay at 600 for 10 minutes. In addition the > spinfo_mtu of the association to 8002 never changes, it stays at the > original 1500. > > The only difference between the two tests is the attempt to connect to a > non-responding IP at the beginning of test 2. Any ideas why the behaviour > changes, is this a bug or is there some other reason for this? > > I have attached the sample application used for reproducing this. Hi, Any input on this? Is this the right forum for this? BR, -Peter -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
