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Tuesday, May 27, 2014

How to use F5 Wireshark Plugin for LTM troubleshooting

In this post we are going to look how to use F5 Wireshark Plugin to troubleshoot networking issues on BigIP LTM.
  • Download the and install the plugin in your Wireshark
The full instruction are here F5 Wireshark Plugin. In essence you needed to copy the f5ethtrailer.dll file into C:\Program Files (x86)\wireshark\wireshark16\WiresharkPortable\ and restart my Wireshark.

Once you restart wireshark go to menu Help - About Wireshark, Plugins tab. You should be able to see the plugin listed there if properly installed.

  • The plugin is useful only if you take a capture on LTM with 'noise' information.
The noise is an internal information that TMM is attaching and managing for every packet when is being processed. To have a capture with noise these are the minimal options you need to specify:

tcpdump -w /var/tmp/capture.pcap -s0 -i _interface_:nnn

where the _interface_ can be:
    •  1.1 - example of an physical interface
    • dmz_vlan - a name you gave to your vlan when created
    • 0.0 - is the equivalent of 'any' interface what means capture on all interfaces and all vlans
My favourite syntax is usually something like this:

tcpdump -s0 -nn -w /var/tmp/test1-$(date +%s).pcap -i 0.0:nnn '(host _ip_ and port _port_ ) or arp or not ip' 
  • Open the capture in wireshark as normal
Once you open you will noticed that there is additional section in the packet details.

  • The most useful part of using this plugin is that you can quickly and easily find the client and server site traffic in the capture (It can be a challenging when you have multiple tcp streams and OneConnect profile):
    • Find a single packet of the flow you are interested in (search for VIP or client ip for example).
    • Find the "Flow ID" from the F5 Ethernet trailer (see the picture above for example).
    • Click with right mouse taste on the Flow ID field and select "Prepare as Filter".
    • In the Filter box (on top ) it will pre-populate the syntax for you.
    • Copy the hex value and delete the '.flowid == hex' part and start typing '.'  (dot).
    • It will mediately give you a list of possible options, select anyflowid and copy the hex back as it was originally. Example:
The original filter         : f5ethtrailer.flowid == 0x0d2e6dc0
Filter after modifications  : f5ethtrailer.anyflowid == 0x0d2e6dc0
    • Press Apply button
This filter is gong to find the client and server site flows for you. You can then analyse them packet by packet to find out and understand how and why LTM load balance it to one or another pool member.

SOL13637: Capturing internal TMM information with tcpdump

1 comment:

  1. can you feed your blog to twitter as well?