Brought to you by Michael and Brian - take a Talk Python course or get Brian's pytest book

#40: Packet Manipulation with Scapy

Published Thu, Aug 24, 2017, recorded Wed, Aug 23, 2017

We have guest hosts filling in for Michael while he is on vacation. This week we have Eric Chou, author of the book “Mastering Python Networking” and a self-proclaimed Network Automation Nerd.

Eric #1: DevOps Automation Tool: Ansible

  • DevOps Automation framework written in Python, code hosted on GitHub.
  • Top 10 OpenSource projects in 2014 by, along with Docker, Kubernetes, Apache Hadoop, OpenStack, and OpenDaylight, etc.
  • Excellent documentation for all modules.
  • Agentless, ‘networking vendor’ friendly, execute code locally that interacts with the device via SSH and API.
  • Lots of Network modules, including Cisco, Juniper, Arista, etc. In fact, you can find Cisco and Juniper testimonial on the Ansible site.
  • Easy to learn and extend if you already know a little bit about Python, YAML, and Jinja2.

Brian #2: Python Practices for Efficient Code: Performance, Memory, and Usability

(I’m too opinionated to leave out my thoughts when covering this article, even though it’s very well written and I mean no disrespect to Satwik Kansal)

  1. Try not to blow off memory
    • use generators to calculate large sets of results
    • for big number crunching, use numpy
    • Use format instead of + for large strings. (or f-strings - Brian)
    • Use slots for classes (psshh, use attrs - Brian)
  2. Python 2 or 3
    • Write code compatible with both. (disagree, use 3 unless you can’t for a very good reason, then write code that’s easy to convert to 3 later. - Brian)
  3. Write Beautiful code because “The first impression is the last impression."
    • follow style guides
    • use static analysis tools. Recommended using something called coala that’s installed as “coala-bears.
    • (Brian: Maintenance cost is a real thing. Make your code look good because it’s cheaper in the long run. Use pycodestyle, pydocstyle, flake8, and if using sublime, use Flake8Lint)
  4. Speed up your performance
    • Multiprocess, not Multi-thread
  5. Analyzing your code
    • Use cProfile, memory_profiler, objgraph, resource
  6. Testing and CI
    • nose or pytest or doctest
    • (Brian: BTW, I really appreciate the links to for tutorials on these.)
    • (Brian: No. Use pytest)
    • measure coverage and and try for 100%
    • (Brian: No. use coverage to be alerted of sudden changes, and of code that possibly needs more testing and/or deleted)

Eric #3: Packet Manipulation Program: Scapy

  • Free Python-based interactive packet manipulation program and library, GitHub.
  • Craft the packet from the ground up, you can use it to decode packets or craft packets.
  • You are in control instead of limited to what the creator of the tool can imagine, i.e. hping3, curl.
  • Can be used together with the Python interpreter.
  • Particularly useful for network security
    • Crafting common attacks: malformed packets (such as IP version 3), Ping of Death (large paylaod), Land Attack (redirect the client response back to the client itself) for denial-of-service.
    • Penetration Testing (TCP port scan) and Fuzzing by providing invalid, unexpected, or random data.

Brian #4: Using Headless Chrome with Selenium

  • Miguel Grinberg quick demo of using headless chrome with selenium and unittest.
  • (Brian: Eventually I’ll get Miguel to use pytest more.)
  • Replace the normal Firefox with Chrome in the webdriver of Selenium, and passing a ‘headless’ argument to make it so the window doesn’t keep popping up and down when testing.

Eric #5: Graph Visualization with Graphviz

  • Open Source graph visualization software.
  • Perfect for graphing the large datacenter topology automatically or any other network diagrams.
  • Extensive documentation and gallery of examples.
  • Did I mention this is ‘automatible’? Thus avoid drifts between reality and actual network.
  • Python package graphviz (lower case g) for Graphviz integration.

Brian #6: PyCascades CFP still open until the 28th

  • Python conference in Vancouver, BC.
  • Talks Jan 22, 23, Sprints Jan 24th
  • Speakers get free admission. Talks are all 25 min slots. No Q&A after talks in front of full audience, but speakers will hang out up front for a few minutes for individual questions
  • I’m going to submit at least one proposal. But I’m kinda swamped this week, so the proposal will unfortunately be rushed.

Extra Eric:

Extra Brian:

Want to go deeper? Check our projects