#40 Packet Manipulation with Scapy

Python Bytes - A podcast by Michael Kennedy and Brian Okken - Lunedì

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Tecnica

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 OpenSource.com, 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 pythontesting.net 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.

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