reassemble large packets in switch mode

[Guus Sliepen]

On Sun, May 14, 2006 at 06:42:01PM +0200, Axel Christiansen wrote:

> i run into trouble using tinc in switch mode.
> Its a simple setup with 2 hosts.
[...]
> Now it seems large packets can not be transmitted.
> I verified it step by step the way with tcpdump.
> A ping with a size larger then 1400 byte gets not
> reassembled in the tincd on host B, no matter witch
> side i use.
> 
> On host A i see the fragmented udp packets arrive,
> assembled to a large ping and show up on the bridge
> interface. Then those pings gets answered and find
> there way back to host B nicely. They arrive on host
> B as udp fragments but then dont show up in the bridge.
> 
> So it seems host B disassembles the packets to udp
> but not reassembles them. At least i can see the pings.
> 
> By the way, it seems the PMTU setting has no affect. I lowered
> the MTU size to 1400, but udp fragments still have a size
> of 1524.

How did you change the MTU? Using the PMTU configuration option or by
setting it with ifconfig? Did you try the PMTUDiscovery option? Ping is
not UDP but ICMP. But in any case, fragmentation is handled at the IP
layer. Is the DF (dont fragment) bit set on the packets you are sending?

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