Note-to-future-self: commands with long output breaking inside nested VPN

Context

2 VPNs, ssh works, but vim/nano/large cat hangs the terminal. Same on scp with large files.
Client-only access to VPN configs

Solution

Add to .ovpn:

tun-mtu 1400
mssfix 1360

Add to ~/.ssh/config

Host *
  ServerAliveInterval 10
  ServerAliveCountMax 5
  TCPKeepAlive yes
  Compression yes