There are multiple options to use SSH in Python but Paramiko is the most popular one. Paramiko is an SSHv2 protocol library for Python. In this lesson, I’ll show you how to use Paramiko to connect to a Cisco IOS router, run a show command, and return the output to us.
Here is the topology:
All you need thereis to make sure that OpenSSH client and Python interpreter are installed, and then install openssh-wrapper package. The OpenSSH Project. OpenSSH has 3 repositories available. Follow their code on GitHub.
Perform commands over ssh with Python. Ask Question Asked 10 years, 8 months ago. Active 13 days ago. Viewed 510k times 159. I'm writing a script to automate some command line commands in Python. At the moment I'm doing calls thus: cmd = 'some unix command' retcode = subprocess.call(cmd,shell=True). In python SSH is implemented by using the python library called fabric. It can be used to issue commands remotely over SSH.
I’ll use a Cisco IOS router running IOS Version 15.7(3)M3 and I’ll run the Python code from my computer.
On the router, we need to enable SSH:
I configured an “admin” user with privilege level 15 so that we have full access to the router once we log in.
We need to install Paramiko, which is easy with PIP:
We are now ready to try some code.
In our first example, here’s what we try to accomplish:
- Connect to the router with username/password authentication.
- Run the
show ip routecommand.
- Look for the default route in the output and show it to us.
Here is my code:
When we run this code, here’s what we get:
This is nice. We managed to connect to the router, run the
show ip route command, and look for the default route.
Improved Sample Code
How could we improve this script with some of the things we learned? For example:
- Our code runs a single command. How about we use a function so we can use our code to connect to different devices and run different commands?
- What if our SSH connection fails? It would be nice to deal with this with a try/except block. How about we try to attempt to connect multiple times?
Let’s see what we can do. Here is my improved code:
What did I change?
- I created a function to contain the code used to connect to the router.
- I added a
try/exceptblock for the connection with multiple attempts. When the connection fails, it shows the reason.
- An extra check to see if the router output contains any information.
Let’s run our code again to see if it works.
When you supply a wrong password, you get this output:
This looks good. Our code attempted to connect three times and showed the reason why it was unable to connect.
When your host is unavailable, you get this output:
Once again, three attempts to connect and it shows the reason why our script failed.
You have now learned how you can connect to a device using SSH and Python. Although this works, it might not be the best solution. In this example, I ran the
show ip route command and looked for the default route. This is simple, but what if you want to parse show commands that have a lot of information?
It’s possible to parse the output of show commands like this using regular expressions but it’s a pain. Instead, if possible, it’s better to use a REST API where the device returns the output in JSON format. Parsing JSON in Python is much easier.
I hope you enjoyed this lesson. If you have any questions feel free to leave a comment!Latest version
Python wrapper module around the OpenSSL library
Note: The Python Cryptographic Authority strongly suggests the use of pyca/cryptographywhere possible. If you are using pyOpenSSL for anything other than making a TLS connectionyou should move to cryptography and drop your pyOpenSSL dependency.
High-level wrapper around a subset of the OpenSSL library. Includes
- SSL.Connection objects, wrapping the methods of Python’s portable sockets
- Callbacks written in Python
- Extensive error-handling mechanism, mirroring OpenSSL’s error codes
… and much more.
You can find more information in the documentation.Development takes place on GitHub.
If you run into bugs, you can file them in our issue tracker.
We maintain a cryptography-dev mailing list for both user and development discussions.
You can also join #cryptography-dev on Freenode to ask questions or get involved.
- The minimum cryptography version is now 3.2.
- Remove deprecated OpenSSL.tsafe module.
- Removed deprecated OpenSSL.SSL.Context.set_npn_advertise_callback, OpenSSL.SSL.Context.set_npn_select_callback, and OpenSSL.SSL.Connection.get_next_proto_negotiated.
- Drop support for Python 3.4
- Drop support for OpenSSL 1.0.1 and 1.0.2
- Deprecated OpenSSL.crypto.loads_pkcs7 and OpenSSL.crypto.loads_pkcs12.
- Added a new optional chain parameter to OpenSSL.crypto.X509StoreContext()where additional untrusted certificates can be specified to help chain building.#948
- Added OpenSSL.crypto.X509Store.load_locations to set trustedcertificate file bundles and/or directories for verification.#943
- Added Context.set_keylog_callback to log key material.#910
- Added OpenSSL.SSL.Connection.get_verified_chain to retrieve theverified certificate chain of the peer.#894.
- Make verification callback optional in Context.set_verify.If omitted, OpenSSL’s default verification is used.#933
- Fixed a bug that could truncate or cause a zero-length key error due to anull byte in private key passphrase in OpenSSL.crypto.load_privatekeyand OpenSSL.crypto.dump_privatekey.#947
- Removed deprecated ContextType, ConnectionType, PKeyType, X509NameType, X509ReqType, X509Type, X509StoreType, CRLType, PKCS7Type, PKCS12Type, and NetscapeSPKIType aliases.Use the classes without the Type suffix instead.#814
- The minimum cryptography version is now 2.8 due to issues on macOS with a transitive dependency.#875
- Deprecated OpenSSL.SSL.Context.set_npn_advertise_callback, OpenSSL.SSL.Context.set_npn_select_callback, and OpenSSL.SSL.Connection.get_next_proto_negotiated.ALPN should be used instead.#820
- Support bytearray in SSL.Connection.send() by using cffi’s from_buffer.#852
- The OpenSSL.SSL.Context.set_alpn_select_callback can return a new NO_OVERLAPPING_PROTOCOLS sentinel valueto allow a TLS handshake to complete without an application protocol.
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