Hello guys.
I have some weird behavior on my CHR (ver. 7.15.2). A few words about my environment - everything in the Hetzner, Mikrotik CHR is VM in Hetzner Cloud and two physical Proxmox servers. They are connected through Hetzner vSwitch, and according to Hetzner documentation configured with MTU 1400(172.16.252.0/23). On top of this LAN created VXLAN (10.100.18.0/24) with MTU 1350. All VMs on Proxmox servers connected to this VXLAN, MIkrotik here plays as NAT and firewall for all these VMs, SNAT for Sites which reside on VMs, etc.
it works great, there are no any issues here.
But I also configured the L2TP+Ipsec server(for me) on Mikrotik CHR for connection to manage all this stuff. And there is an issue after connecting to L2TP(or disconnecting) I get plodding VXLAN performance, dropping connections to VMs, users(they are connected from the Internet, they don’t use l2tp vpn) report that sites start lagging. If I connect to the console to any VM and for example run a speed test, I get 900Mb/s for download and ~0.05-0.2 Mb/s for upload.
I accidentally discovered in order to fix it need to up/down VXLAN interface on Mikrotik, or change MTU on Mikrotik VXLAN interface(for example to 1349 and then back to 1350), any action that reloads VXLAN interface on Mikrotik.
Everything continues to work fine until I connect or disconnect the L2TP VPN again.
I ran Wireshark on one of the VM when the issue was present and noticed that there were a lot of packages “This frame is a (suspected) retransmission” and “TCP reset”.
But as soon as I reload the VXLAN interface, everything is back to normal.
Could you please help me solve the root issue, I can’t understand how connection/disconnection to L2TP can break the VXLAN and in general what the two have in common.