Packet reordering problem?

[Guus Sliepen]

On Mon, May 18, 2015 at 12:08:53PM +0200, Armin Schindler wrote:

> We didn't change that [ReplayWindow] setting, so the default is 16.
> What exactly will happen if tinc gets a packet which should have arrived
> 20 packtes before (because of the TOS prio queues)?

With the default setting of 16, up to 128 packets can be arbitrarily reordered
without problems. If a packet arrives that is 129 packets late, then it
will be dropped. Tinc will also log a warning whenever it encounters a
late packet.

> Since I activated the prio queues (VoIP packets get highest prio
> on eth and tinc device via TOS value), we encountered instability:
> We have 6 nodes connected via tinc. If one node becomes unreachable
> (internet connection down), normal encrypted packets from/to other nodes
> seem to be hanging. Just the high prio VoIP packets seem to be forwarded
> by tinc like normal.
> Example of nodes A,B,C,D,E and F: A becomes unreachable and suddenly
> connections (except high prio queue packets) from B to C, and B to D and C
> to D, etc. have massive packet loss.
> As soon as A is back online, all goes normal.

Hm. It would be nice to know how your nodes connect to each other. And
what do you mean with massive packet loss? 100%?

> Could there be an internal queue togehther with the reordering be the cause?

Tinc itself doesn't queue packets. But your prio queues do by
definition. So how large are those? Also, do you have a lot of VoIP
traffic? If it's more than the available bandwidth, then the prio queues
could indeed cause all other traffic to be dropped.

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