Occasionally I've seen issues with Joyent smartmachines (= Solaris zones) where SSH stops working, even though SSH is still listening.
An ssh attempt then looks like this:
ssh_exchange_identification: Connection closed by remote host
To solve this issue, the SMF service "smartlogin" needs to be restarted on the physical server on which this smartmachine resides.
[root@computenode003 ~]# svcadm restart svc:/smartdc/agent/smartlogin:default
The SSH login into the smartmachine should then work again:
Last login: Fri Jan 31 08:51:36 2014 from xxx.xxx.xxx.xxx