Paramiko : Error reading SSH protocol banner

Adding to TinBane's answers, suggesting to edit transport.py: you don't have to do that anymore.

Since Paramiko v. 1.15.0, released in 2015, (this PR, to be precise) you can configure that value when creating Paramiko connection, like this:

client = SSHClient()
client.connect('ssh.example.com', banner_timeout=200)

In the current version of Paramiko as of writing these words, v. 2.7.1, you have 2 more timeouts that you can configure when calling connect method, for these 3 in total (source):

• banner_timeout - an optional timeout (in seconds) to wait for the SSH banner to be presented.
• timeout - an optional timeout (in seconds) for the TCP connect
• auth_timeout - an optional timeout (in seconds) to wait for an authentication response.

It depends on what you mean by "fix". The underlying cause, as pointed out in the comments, are congestion/lack of resources. In that way, it's similar to some HTTP codes. That's the normal cause, it could be that the ssh server is returning the wrong header data.

429 Too Many Requests, tells the client to use rate limiting, or sometimes APIs will return 503 in a similar way, if you exceed your quota. The idea being, to try again later, with a delay.

You can attempt to handle this exception in your code, wait a little while, and try again. You can also edit your transport.py file, to set the banner timeout to something higher. If you have an application where it doesn't matter how quickly the server responds, you could set this to 60 seconds.

EDIT: Editing your transport file is no longer needed as per Greg's answer. When you call connect, you can pass a banner_timeout (which solves this issue), a timeout (for the underlying TCP), and an auth_timeout (waiting for authentication response). Greg's answer has a code example with banner_timeout that you can directly lift.