Re: TCP reassembly fails when ethernet tunnled over TCP

[John Thacker <johnthacker () gmail com>]

Yes, this is a long standing problem:

https://gitlab.com/wireshark/wireshark/-/issues/2345
and
https://gitlab.com/wireshark/wireshark/-/issues/9782

among others, are examples of the same generic problem.

The entire packet_info [dl_|net_]{src, dst} structure doesn't work very
well for tunnelled packets, especially those containing the same protocol
in the outer layers as well inside the tunnel. The endpoints API is
supposed to help, but the TCP dissector doesn't use it, and it would still
have to be changed for multiple protocols of the same type, see Michael
Mann's comment on #2345.

John


On Fri, Nov 12, 2021 at 7:57 AM Anders Broman via Wireshark-dev <
wireshark-dev () wireshark org> wrote:

> Hi,
>
> We have a proprietary protocol sending usually small frames mixed with
> larger tunneled ethernet frames over TCP. If we then have a TCP segment
> where the ethernet frame
>
> Spans 2 segments reassembly fails presumably because pinfo does not have
> the IP address of the TCP segment. I think we would need a way to create a
> new pinfo structure
>
> For the tunneled frame? How to do that or some other way to solve the
> problem? In our case we only have ethernet and a vlan tag then our protocol
> again so
>
> We “fixed” that by dissecting those bytes in the internal dissector. But I
> think it may be a generic problem for tunneling that may deserve a proper
> fix.
>
> tcp_dissect_pdus() is used
>
> Regards
>
> Anders
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