ssh legacy option

some older ssh server only support limited key exchange algorithm.

When you get this error:

no matching key exchange method found. Their offer: diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1

Use this option :
-oKexAlgorithms=+diffie-hellman-group1-sha1

eg:

ssh -oKexAlgorithms=+diffie-hellman-group1-sha1 user@legacyhost

or put this in your .ssh/config file:

Host myhost.example.org
 KexAlgorithms +diffie-hellman-group1-sha1

ref: https://www.openssh.com/legacy.html