Cookie Persistence and Troubleshooting

The BIG-IP persistence cookie is a valuable configuration option that allows stateful applications to remain persistent to a specific node with no additional configurations within the application or on the server(s) by doing something like clustering.

I hear application development teams refer to this as “sticky session” or “stick sessions”, but in reality this cookie has nothing to do with a user’s “application” session, but has everything to do with the user’s session persistence to the same server that the application session was started on.

After reading an F5 Solution article (SOL6917: Overview of BIG-IP persistence cookie encoding) and learning that the information encoded within a BIG-IP Cookie could be useful I decided to make a tool that could decipher this information quickly so that I could use it for troubleshooting.

What is useful in a BIG-IP Cookie?

The BIG-IP Cookie contains the IP Address of the server that the client is being persisted to, as well as the server port that the connection is being established on.

So? Why is this useful? I could get that information from an iRule…

True, you can get this information logged within the LB::selected event within an iRule, but that requires you to make an iRule change to gather the information that you actually already have (unless you are encrypting your BIG-IP Cookies which negate the usefulness of this tool). Most changes in Production require change management approval, which you get to bypass when using this tool if cookie persistence is configured.

There are many tools that you can use to capture the persistence cookie being provided by the BIG-IP. I commonly use Fiddler2 (…



This is the application that I created to decipher the BIG-IP Cookies.



The tool is semi-intelligent for the input. It can take any of the following and give the correct output:

Paste the cookie into the tool and select ‘Auto-Parse’ option:



This will populate the Conversion Area:



Then select the ‘Decipher’ option:



This becomes useful for troubleshooting purposes to determine which server you are persisted to when you are trying to determine which member server is or is not having an issue.

As you can see, this correctly identified which server I was communicating with in this pool of servers:



I hope that everyone finds this tool useful.

If you find any issues or have any questions please feel free to contact me on DevCentral.

Source Code

The full source for this application can be retrieved at this link:

Published Aug 08, 2011
Version 1.0

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  • Does this tool handle the cookie format changes when using route domains?
  • Unfortunately No. It was only designed to decipher the default (IPv4) persistence cookie.



    There is no reason why you couldn't add to it though using the information provided in the overview of the Persistence Cookie.



    SOL6917: Overview of BIG-IP persistence cookie encoding

  • dasz's avatar
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    For some reason it cannot decipher valid cookie: BIGipServerP80_pool1=185860362.20480.0000


  • Its seems you have missed one digit while decoding that. Please check and tried one more time it will work for you also.


    i used same value which you provided in the comments


    You mentioned BIGipServerP80_pool1=185860362.20480.0000


    Added another digit BIGipServerP80_pool1=1858603621.20480.0000 IP address Port 80


  • pr's avatar
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    Working fine for me thanks for sharing this tool