Not able to ssh to the server [closed] - ssh

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not able to login into server through ssh. so logged in with rsh and when trying to ssh host itself getting error :
no common kex alg: client 'diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1', server 'gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g=='
I found this log in /var/svc/log/network-ssh:default.log
[ May 14 21:23:13 Rereading configuration. ]
[ May 14 21:23:13 Executing refresh method ("/lib/svc/method/sshd restart") ]
[ May 14 21:23:13 Method "refresh" exited with status 0 ]
[ May 14 21:30:25 Stopping because service disabled. ]
[ May 14 21:30:25 Executing stop method (:kill) ]
[ May 14 21:33:08 Enabled. ]
[ May 14 21:33:08 Executing start method ("/lib/svc/method/sshd start") ]
Could not load host key: /.ssh/id_dsa
Could not load host key: /.ssh/identity
Disabling protocol version 1. Could not load host key
[ May 14 21:33:08 Method "start" exited with status 0 ]
thanks in advance.

Answer 1

Looks like the server and client don’t find a common authentication method.
I just got that with a sun cluster here: It only supports diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1, but my Gentoo GNU/Linux ssh server seems to have dropped the group1 algo.
Fixed by changing /etc/ssh/sshd_config on the ssh server to include
KexAlgorithms curve25519-sha256#libssh.org,diffie-hellman-group1-sha1,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1,diffie-hellman-group-exchange-sha256,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521
I fear, though, that there was a reason for removing the group1 algorithm from the default. I would not do this on a publicly accessible box.
For reference also see https://security.stackexchange.com/questions/25662/openssh-default-preferred-ciphers-hash-etc-for-ssh2

Answer 2

Turn on verbose ssh which will hopefully show where the issue is.
E.g.
ssh -v host
If that doesn't give enough info, you can try
ssh -vv host
or even
ssh -vvv host
Look for the first error in the output which will hopefully give you clues as to where the issue lies.