Packet reordering problem?

[Armin Schindler]

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Hello Guus,

On 04/30/2015 03:42 PM, Guus Sliepen wrote:
> On Thu, Apr 30, 2015 at 02:55:59PM +0200, Armin Schindler wrote:
> 
>> we are using tinc 1.0.24 with 6 hosts (endpoints). Quality of service
>> is used with prio qdisc on all network interfaces. This means depending
>> on the TOS value of the IP header IP-packets will get a priority queue
>> on the network interface.
>> 
>> Packets from TINC (UDP 655) maybe reordered using these queues to send
>> out high-prio (VoIP) packets first. Could this create a problem on the
>> receiving tincd? I guess the sequence number is checked here, right?
> 
> Tinc checks the sequence number, but allows reordering up to a certain 
> number of packets. Have a look at the ReplayWindow configuration option 
> in the manual:
> 
> http://tinc-vpn.org/documentation/Main-configuration-variables.html#index-Re
playWindow

we
> 
didn't change that 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)?

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.

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

Armin
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