Hi Andreas,
The tracing should work but because we’re reusing the syn packet to build the
syn-ack, it might not show correctly. Could you breakpoint the tcp4-output and
try to see if the trace code is hit?
As for the checksum, tcp only tags the packet with a request to have it
offloaded. If the nic wrongly advertises that it can do it, the offload
infrastructure will comply with that.
If you’re using dpdk and you want to force sw checksum computation, change
startup conf and add "dpdk { enable-tcp-udp-checksum }”.
Hope this helps,
Florin
> On Apr 29, 2019, at 6:31 AM, Andreas Schultz <andreas.schu...@travelping.com>
> wrote:
>
> Hi,
>
> I'm trying to debug a problem and need to trace tcp4-output with vpp 19.04.
>
> So far I have tried it with "trace add tcp4-output 100 verbose", but that is
> not producing the expected result. The trace buffer is always empty.
>
> I was expecting that "trace add af-packet-input 100" would also trace the
> replies. But I can only see the incoming TCP-SYN, the generated SYN+ACK and
> the tcp4-output nodes are not showing up in the trace.
> I do know that the SYN+ACK gets generate, because I can see it in tcpdump
> after it has gone through an encapsulation.
>
> The problem I'm trying to figure out is why the TCP SYN+ACK packet when it
> hits a tunnel encapsulation node has invalid (or even no) check sums. I
> suspect there is something going on with the csum offload. But without the
> trace, finding that problem is a nightmare.
>
> Many thanks,
> Andreas
>
>
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> Dipl.-Inform. Andreas Schultz
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