Wednesday, July 15, 2015

Installing netmiko on Windows

Netmiko is a Python module by Kirk Byers that provides a wrapper around the Paramiko SSH module for doing screen scraping and CLI automation on network devices.

Paramiko has some dependencies that make installation on Windows a tad tricky. Here's a quick way to get it done:

  1. Install Anaconda.
  2. From the Anaconda shell, run "conda install paramiko".
  3. From the Anaconda shell, run "pip install scp".
  4. Install git for Windows.
  5. Clone netmiko with "git clone"
  6. cd into the netmiko directory and run "python install".
Done! Screen scrape away, and don't forget to hound your vendors for real APIs... :-)

Tuesday, July 14, 2015

Extracting Traffic from Rolling Capture Files

Every so often I need to extract a subset of traffic from a set of rolling timestamped pcap files. One common place I do this is with Security Onion; one of the great features of SO is its full-packet-capture feature: you can easily pivot from Snort, Suricata, or Bro logs to a full packet capture view, or download the associated pcap file.

But what if you don't have an associated alert or Bro log entry? Or if you're doing pcap on some system that's not as user-friendly as Security Onion, but nonetheless supports rolling captures?

The way I usually do this is with find and xargs. Here's an example of my most common workflow, using timestamps as the filtering criteria for find:

> find . -newerct "16:07" ! -newerct "16:10" | xargs -I {} tcpdump -r {} -w /tmp/{} host
> cd /tmp
> mergecap -w merged.pcap *.pcap

  1. Find all files in the current directory created after 16:07 but not created after 16:10. This requires GNU find 4.3.3 or later. It supports many different time and date formats.
  2. Using xargs, filter each file with the "host" BPF expression and write it to /tmp with the same filename.
  3. Merge all the .pcap files in /tmp into merged.pcap.
You can easily modify this workflow to fit other use cases.