[strongSwan] Packets get lost in one direction (MTU?)
catscrash at catscrash.de
Sat Nov 30 23:31:15 CET 2019
I have an issue with one of my tunnels. On both side installed is
strongswan 5.5.1-4+deb9u4 on Debian 9.
Here is the config
Other side looks like that, with left and right switched.
Ping works from A to B and from B to A.
When I ssh from B to A, it works, but as soon as I have a larger
terminal output the connection breaks.
When I ssh from A to B, everything works fine.
When I do a scp on server B to push a file to server A, everything works
fine, even for huge files.
When I do a scp on server B to pull a file from server A, it breaks
after a few bytes and doesn't continue.
I thought this sounds like a MTU issue. I tried setting
fragmentation=yes, which did not help. The external interfaces on both
sides have mtu 1500 set, at least that's what "ip link show" says.
I tried to find out which MTU would work with the ping -M do -s command.
And it seems everything above 1410 causes trouble. So I guess setting it
to 1400 would be fine... But how? I'd rather not set the external
interface MTU, since there are a lot of other tunnels on those servers
that work just fine except for this one
Thanks for any help!||||
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