[Pkg-swan-devel] Bug#874503: warn about unsupported kernel versions

[Daniel Pocock]

Package: strongswan
Version: 5.5.1-4+deb9u1


There is some issue with kernel version 4.11

strongswan wasn't working, I looked with tcpdump and saw messages like
"truncated-udplength 0"

I used a search engine to find out about that string and it took me to
this page:

https://www.linuxquestions.org/questions/linux-networking-3/strongswan-ikev2-clients-can-access-everything-but-strongswan-machine-itself-truncated-udp-length-0-a-4175606751/

with the quote "So this appears to be a kernel-related issue; I had
updated to 4.11.2 recently. Downgrading back to 4.10.9, without any
other changes to my setup, resolves the problem."

I downgraded my own system to a 4.9 kernel and it worked again.

There was no obvious error from StrongSWAN in the console or in the logs
to tell me about this, I can imagine some people losing a lot of time on
something like this if they don't come across this page.

Regards,

Daniel