Periodically get SSH Protocol Error

When attempting to connect to a Cisco IOS device, I am almost always getting the error listed below, and every now and then it will just work. It is exactly the same issue as #883 however changing global_delay_factor nor blocking_timeout seems to change the consistency of being able to connect.

An interesting note, once I connect once I seem to be able to connect repeatedly without issue. Another not that I’m unsure if it is relevant or not, I am using a tunnel to connect:

sshtunnel -v -L 0.0.0.0:10022 -R endhost:22 -U jumphostusername -P jumphostpassword jumphost

And connecting with:

ConnectHandler(device_type="cisco_ios", ip="127.0.0.1", port=10022, username="endhostusername", password="endhostpassword", secret="secret", timeout=30, global_delay_factor=3)

Traceback:

Traceback (most recent call last):
  File ".../.python/lib/python3.6/site-packages/paramiko/transport.py", line 2138, in _check_banner
    buf = self.packetizer.readline(timeout)
  File ".../.python/lib/python3.6/site-packages/paramiko/packet.py", line 370, in readline
    buf += self._read_timeout(timeout)
  File ".../.python/lib/python3.6/site-packages/paramiko/packet.py", line 568, in _read_timeout
    raise EOFError()
EOFError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ".../.python/lib/python3.6/site-packages/paramiko/transport.py", line 1966, in run
    self._check_banner()
  File ".../.python/lib/python3.6/site-packages/paramiko/transport.py", line 2143, in _check_banner
    "Error reading SSH protocol banner" + str(e)
paramiko.ssh_exception.SSHException: Error reading SSH protocol banner

Traceback (most recent call last):
  File ".../.python/lib/python3.6/site-packages/paramiko/transport.py", line 2138, in _check_banner
    buf = self.packetizer.readline(timeout)
  File ".../.python/lib/python3.6/site-packages/paramiko/packet.py", line 370, in readline
    buf += self._read_timeout(timeout)
  File ".../.python/lib/python3.6/site-packages/paramiko/packet.py", line 568, in _read_timeout
    raise EOFError()
EOFError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../.python/lib/python3.6/site-packages/netmiko/ssh_dispatcher.py", line 228, in ConnectHandler
    return ConnectionClass(*args, **kwargs)
  File ".../.python/lib/python3.6/site-packages/netmiko/base_connection.py", line 312, in __init__
    self.establish_connection()
  File ".../.python/lib/python3.6/site-packages/netmiko/base_connection.py", line 858, in establish_connection
    self.remote_conn_pre.connect(**ssh_connect_params)
  File ".../.python/lib/python3.6/site-packages/paramiko/client.py", line 397, in connect
    t.start_client(timeout=timeout)
  File ".../.python/lib/python3.6/site-packages/paramiko/transport.py", line 587, in start_client
    raise e
  File ".../.python/lib/python3.6/site-packages/paramiko/transport.py", line 1966, in run
    self._check_banner()
  File ".../.python/lib/python3.6/site-packages/paramiko/transport.py", line 2143, in _check_banner
    "Error reading SSH protocol banner" + str(e)
paramiko.ssh_exception.SSHException: Error reading SSH protocol banner

Since it seems to be failing here: https://github.com/paramiko/paramiko/blob/master/paramiko/packet.py#L561 I have attempted to print x and when it fails it’s, of course, empty bytes…when it succeeds it reads b'SSH-2.0-Cisco-1.25\n' I don’t know if it helps or not, but it’s the farthest I can think of to troubleshoot since I’m not sure why this is happening.

[Alan-R]

I have seen this happen a lot when testing against Linux Docker containers if I connect too soon after I booting them up. I put a workaround in my code to recognize it and try again.

[ktbyers]

Added support for banner_timeout argument to the develop branch in Netmiko:

https://github.com/ktbyers/netmiko/pull/1264

Please test and see if increasing this helps. I also set the default banner_timeout to 5 seconds which is greater than the Paramiko uses (paramiko uses 2 seconds by default).

If you are still seeing an issue re-open this issue.