This config solved my SSH connection problem with M1 fibre broadband network (on a Huawei HG256 residential gateway device) that I'm currently using

config

# SSH Connection pooling for faster additional connections to a machine
ControlMaster auto
ControlPath /tmp/ssh_mux_%h_%p_%r

# This makes subsequent connections go faster
ControlPersist 2h

# Make it so ssh-ing from one server to another passes keys around automagically
Host *
ForwardAgent yes

# Get rid of SSH connection delays
GSSAPIAuthentication no

# Stop timing out connections
ServerAliveInterval 300
ServerAliveCountMax 20

# Use less encryption on servers I cant get to off-network
Host nf* 10.* 172.* 192.168.*
Ciphers blowfish-cbc

Thanks for the config