Reliability of Tinc under load

[Saverio Proto]

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 <dominik.george at teckids.org>:
> 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
> tinc at tinc-vpn.org
> http://www.tinc-vpn.org/cgi-bin/mailman/listinfo/tinc
>