ssh_exchange_identification: Connection closed by remote host

Problem:

After upgrading openssh to version 5 on AIX server. Got the following error when trying to ssh into it.

$ ssh -l userid server
ssh_exchange_identification: Connection closed by remote host

Cause:

Somebody installed TCP wrapper which create a /etc/hosts.allow file with sample setting in it.

# cat /etc/hosts.allow
ALL: LOCAL @some_netgroup
ALL: .foobar.edu EXCEPT terminalserver.foobar.edu
telnetd: toto@foo.foobar.edu, [3ffe:302:100::]

Solution:

Modify the /etc/hosts.allow to allow ALL

# cat /etc/hosts.allow
ALL:ALL

Restart sshd,

stopsrc -s sshd ; startsrc -s sshd

problem fixed.