ssh config for multiple ssh keys

Question

I have the following ssh config file:

Host git.github.com
                User git
                IdentityFile ~/.ssh/id_rsa
Host git.assembla.com
                User git
                IdentityFile ~/.ssh/id_rsa_assembla
Host XXX.XXX.XXXX.group
                IdentityFile ~/.ssh/id_rsa_gerrit
                User xxxx

But when I try and log in, I get:

Unable to negotiate with XX.XXX.XXX.XXX port XXXX: no matching key exchange method found. Their offer: diffie-hellman-group1-sha1 fatal: Could not read from remote repository.

Answer 1

The key exchange method diffie-hellman-group1-sha1 is obsolete. You should update your server to support something more recent.

To connect to this host, you can workaround it by setting

KexAlgorithms diffie-hellman-group1-sha1

to your Host block in ssh_config, as described in the official Legacy page on OpenSSH.