Port 22 actually is for SSH.
Port 23 is used for Telnet.
You say snapshot failed. that is too vague to provide you with any help.
Tell us how it failed, What error messages you are seeing? Is there anything in the transcript? If so what is in the last section before the logout? (BNA always tries to logout so generally you can ignore this section)
I have created several Device interaction troubleshooting videos Start there then if you can't figure it out please provide more details.