You’re trying to SSH to a Zyxel switch and get the following message:
user@hostname ~ $ ssh admin@x.x.x.x -p 22 ssh_dispatch_run_fatal: Connection to x.x.x.x port 22: DH GEX group out of range
Solution:
ssh -o KexAlgorithms=diffie-hellman-group14-sha1 -o HostKeyAlgorithms=+ssh-dss user@x.x.x.x
Reference:
https://serverfault.com/questions/729033/ssh-dh-gex-group-out-of-range