MTU probes fail on reconnect

[Donald Pearson]

On Sat, Jan 1, 2011 at 2:47 PM, Guus Sliepen <guus at tinc-vpn.org> wrote:

>
> If MTU probes are not responded to, then yes, tinc will fall back to TCP
> and
> this will increase latency and decrease throughput. It would be interesting
> to
> know why the MTU probes or the responses to them are not received. Perhaps
> you
> can store tinc's debug output (using the --logfile option) and at the same
> time
> run tcpdump on the public network interface to see what is being sent and
> received?
>

Sure I can do that.  I'll try to get it done this week.

>
> MTU probes will be attempted again after one hour by default. It is tied to
> the
> session key timeout, so you can let tinc try more often by adding KeyExpire
> =
> 600 to tinc.conf for example. Still, this is suboptimal of course. I will
> change it to keep sending MTU probes every PingInterval, just like it does
> when
> MTU probes did not fail.
>

Ah okay.  I definitely didn't observe for an hour.

>
> Hm, that might indicate a bug in tinc. However, I could not reproduce it
> with
> two Linux machines. It could also be a problem with some stateful firewall
> rule
> or a router doing NAT that keeps an old mapping around for 30 seconds.


> > Every time when the MTU probing fails, I see latency between 700 - 1000
> ms
> > with 32 byte pings over a LAN.
>
> That in itself is way too high, but this is a problem many people have seen
> on
> Windows.
>
> Yes, the idea is that tinc should figure out the best way to connect to
> other
> nodes on its own of course. I'll try to reproduce the problem with a node
> running Windows, maybe that makes a difference.
>

Yes this whole thing could very well be related to a Windows client and
perhaps it's related to some of the other complaints I've also seen of other
Windows users report nasty latency.

I will see if I can reproduce the effect with a Linux client too.

-Donald

>
> --
> Met vriendelijke groet / with kind regards,
>     Guus Sliepen <guus at tinc-vpn.org>
>
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