Using Telnet and SSH to test the Transport Layer

Routing & Switching
1

Hello Everyone,

I’ve been able to test the tranport layer using the telnet command. This works great.

For example:

Router1#telnet 192.168.69.93 80 /vrf Mgmt-intf
Trying 192.168.69.93, 80 ... Open

However, I’ve been unable to do the same with SSHv2 it seems the syntax is different?

Router1#ssh -p 80 -vrf Mgmt-intf 192.168.69.93

However, it just hangs and never shows open?

Is it possible?

Best Regards,
John

2

Hello John

Telnet can indeed be useful to test the state of TCP ports on remote devices. More detail on how this can be achieved can be found at this NetworkLessons note.

Unfortunately, SSH does not respond in the same way as Telnet, so it cannot be used to test ports in the same way. This simply has to do with the way in which Telnet and SSH have been designed, and what kind of responses and prompts are actually displayed in the CLI under various circumstances.

Note that the Telnet protocol is not designed for this, but it is simply “good luck” that engineers decided to make Telnet respond the way it does, so it can be helpful in this way.

I hope this has been helpful!

Laz

3

Thank you Sir for that answer. I figured that was the case.

1 Like