Hello, your 1492 makes no sense to me. Maybe you wanted to ping with size 1472 to check a MTU of 1500?
please have a look at this presentation: http://battlemesh.org/BattleMeshV7/Agenda?action=AttachFile&do=view&target=IPv6andMTU.pdf Cheers Saverio 2014-10-29 10:59 GMT+01:00 Dominik George <[email protected]>: > Hi, > >> Couldn't this be a PMTU issue? My guess is that Tinc's UDP packets are >> being silently dropped on the path when they reach a certain size. From >> my experience, Tinc is generally clever about figuring out the optimal >> packet size, but you never know. > > I do not really know how to find out if that is (part of) the issue, I > did my best like so: > > # ip link show tap0 > 7: tap0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast > state UP mode DEFAULT group default qlen 100 > link/ether be:12:4a:bd:4b:40 brd ff:ff:ff:ff:ff:ff > > # ping -M do -s 1492 > terra > PING terra.lan.teckids.org (172.30.254.254) 1492(1520) bytes of data. > ping: local error: Message too long, mtu=1500 > ping: local error: Message too long, mtu=1500 > ping: local error: Message too long, mtu=1500 > > # ping -M do -s 1400 > terra > PING terra.lan.teckids.org (172.30.254.254) 1400(1428) bytes of data. > From terra.lan.teckids.org (172.30.254.254) icmp_seq=1 Frag needed and > DF set (mtu = 1381) > ping: local error: Message too long, mtu=1381 > ping: local error: Message too long, mtu=1381 > > # ping -M do -s 1200 > terra > PING terra.lan.teckids.org (172.30.254.254) 1200(1228) bytes of data. > 1208 bytes from terra.lan.teckids.org (172.30.254.254): icmp_seq=1 > ttl=64 time=44.0 ms > > > That looks strange to me. Where is that final MTU of 1381 enforced? Why > does it change over time? > > Could it be possible that Tinc did its PMTU discovery magic in that moment? > > I remember that the issues I described magically vanish if a ping is > running at the same time ... > > > Cheers, > Nik > > -- > Dominik George (Vorstandsvorsitzender, Pädagogischer Leiter) > Teckids e.V. - Erkunden, Entdecken, Erfinden. > https://www.teckids.org > > > > _______________________________________________ > tinc mailing list > [email protected] > http://www.tinc-vpn.org/cgi-bin/mailman/listinfo/tinc > _______________________________________________ tinc mailing list [email protected] http://www.tinc-vpn.org/cgi-bin/mailman/listinfo/tinc
