Fail to re-use SSH session when connecting to Cisco C2960 switcher

[yegle]

Here's my code:

#!/usr/bin/python26

import paramiko

ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())

ssh.connect('1.2.3.4',username='xxx', password='xxxx',allow_agent=False)
stdin, stdout, stderr = ssh.exec_command('show version')
stdin, stdout, stderr = ssh.exec_command('show mac brief')

result in:

Traceback (most recent call last):
  File "./test.py", line 10, in <module>
    stdin, stdout, stderr = ssh.exec_command('show mac brief')
  File "/usr/lib/python2.6/site-packages/paramiko/client.py", line 363, in exec_command
    chan = self._transport.open_session()
  File "/usr/lib/python2.6/site-packages/paramiko/transport.py", line 658, in open_session
    return self.open_channel('session')
  File "/usr/lib/python2.6/site-packages/paramiko/transport.py", line 746, in open_channel
    raise e
EOFError

[msuberrivs]

I got this problem too. How did you fix it?

[urban-1]

Hi all,

I got this too...

A workaround is to use invoke_shell and work the returned channel like expect: set a time-out and read until you get the prompt. Don't forget to read/empty the buffer after login (and do terminal length 0)! This works for Alcatel too (with env no more) but I think in this case it fails from the 1st issued command (I don't remember, I can test and come back to this if needed). Also, debugging a bit the channel created by invoke_shell I noticed that the characters are returned 1-by-1 - not sure if it is relevant... but the channel timeout seems to not reset when a character is received (the timeout is for the whole process and the channel will close even if the device is still sending characters - I have to test this more)

It would be really good to see this fixed since detecting prompts is very hacky and time-out has to be tuned for specific commands (Alcatel admin display-config takes more than 2 minutes in some cases).

Andreas

(Testing with python 2.7 and 3.4)

[zodiacsmash]

The most likely reason for the EOFError is that the device does not support an SSH channel 'exec' request - which is what exec_command() is attempting - and drops the connection.

The Cisco documentation for 2960-C SSH capability states (under limitations) that :

"SSH supports only the execution-shell application"

which presumably means that - as mentioned above - invoke_shell() is the Paramiko command to use. For details on this I searched for Paramiko SSH Network Devices and found some useful resources.

[bskinn]

@jun66j5 -- if this issue is also due to a Cisco-specific behavior, should we close it also?

[jun66j5]

@bskinn Yes. We should close it also. That is an issue of Cisco device, not an issue of ssh client.