Stalled SSH connections

I spent some time adjusting my SSH configuration because I often get stalled connections to my servers but I never got that fixed until recently, when I started looking in my firewall settings on the pfSense.

After changing the Firewall Optimization Settings within System → Advanced → Firewall & NAT to Conservative I had no more of these hangs of my SSH sessions.

I use the ControlMaster setting in my SSH configuration so the stalled connections have to be killed with something like

$ ssh -O exit {short hostname}

every time – which is annoying.

It got better, but I still experience the one or other hang.

I added/modified these entries within Host * in ~/.ssh/config on the client:

ServerAliveInterval 100
ServerAliveCountMax 10000

and made these changes/additions in /etc/ssh/sshd_config on the server:

ClientAliveInterval 60
ClientAliveCountMax 10000
TCPKeepAlive yes