I don't see any difference.
EX4200-2 is trying to login to EX4200-1, first with a user that is not configured(no-user) and then with a user from 'unauthorized' class(una-user). I put on purpose a wrong password when I tried to login with una-user.
{master:0}[edit]
root@EX4200-1# May 30 10:53:28 EX4200-1 last message repeated 2 times
May 30 10:53:37 EX4200-1 sshd[61412]: %AUTH-6: Failed password for no-user from 172.30.145.204 port 54833 ssh2
May 30 10:53:37 EX4200-1 sshd: %AUTH-5-SSHD_LOGIN_FAILED: Login failed for user 'no-user' from host '172.30.145.204'
May 30 10:53:40 EX4200-1 sshd: %AUTH-5-SSHD_LOGIN_FAILED: Login failed for user 'no-user' from host '172.30.145.204'
May 30 10:53:40 EX4200-1 sshd[61412]: %AUTH-6: Failed password for no-user from 172.30.145.204 port 54833 ssh2
May 30 10:53:59 EX4200-1 sshd: %AUTH-5-SSHD_LOGIN_FAILED: Login failed for user 'no-user' from host '172.30.145.204'
May 30 10:53:59 EX4200-1 sshd[61412]: %AUTH-6: Failed password for no-user from 172.30.145.204 port 54833 ssh2
May 30 10:54:14 EX4200-1 sshd: %AUTH-5-SSHD_LOGIN_ATTEMPTS_THRESHOLD: Threshold for unsuccessful authentication attempts (3) reached by user 'no-user'
May 30 10:54:14 EX4200-1 sshd[61412]: %AUTH-6: Disconnecting: Too many password failures for no-user [preauth]
May 30 10:54:14 EX4200-1 inetd[1285]: %DAEMON-4: /usr/sbin/sshd[61412]: exited, status 255
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root@EX4200-1#
{master:0}[edit]
root@EX4200-1# May 30 10:56:10 EX4200-1 sshd: %AUTH-5-SSHD_LOGIN_FAILED: Login failed for user 'una-user' from host '172.30.145.204'
May 30 10:56:10 EX4200-1 sshd[61809]: %AUTH-6: Failed password for una-user from 172.30.145.204 port 57583 ssh2
May 30 10:56:22 EX4200-1 sshd[61809]: %AUTH-6: Accepted password for una-user from 172.30.145.204 port 57583 ssh2
{master:0}[edit]
root@EX4200-1#
After you login with an unauthorized class user, this is what you get:
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root@EX4200-2# run ssh una-user@172.30.145.153
una-user@172.30.145.153's password:
--- JUNOS 12.3R5.7 built 2013-12-18 01:32:43 UTC
warning: user "una-user" does not have a valid login class
error: Unable to authenticate: bad auth parameter.
Login as root and 'commit' the configuration.
{master:0}
una-user@EX4200-1> exit
Connection to 172.30.145.153 closed.
{master:0}[edit]
root@EX4200-2#
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If this worked for you please flag my post as an "Accepted Solution" so others can benefit. A kudo would be cool if you think I earned it.