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
-oKexAlgorithms=+diffie-hellman-group1-sha1
eg:
or put this in your .ssh/config file:
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