I’ve a main router using VyOS. This router is a Wireguard server (wg01) and is also connected to an OpenVPN server as a client (vtun1). I can’t change anything on OpenVPN server (external resource).
When I scp on router to a computer on vtun1 network, transfer speed is good (as expected). However, if I run the same scp command on a client connected to Wireguard server, speed is more than ten times lower.
I guess (but I’m not sure), the issue is related to MTU vtun1 has a MTU of 1500 and wg01 has a MTU of 1420. Maybe I need to enable TCP-MSS Clamping on router ?
Can you use iperf3 on both sides to test? If it would be the MTU, you would lose all connections greater than 1420 bytes of payload. Have you checked that the responses for the requests sent on wg01 also come back on wg01? You can see the plaintext traffic via tcpdump if necessary too. (e.g. tcpdump --e -i wg01 host x.x.x.x).
So, try to record that traffic and we go from there.
Can you please record it into a file, just use -s 80 or so limit the size. Your posted information doesn’t contain the mac address (-e), which can show sometimes if you have a routing issue.