source address persistence maximum session timeout

Hello,

Generally speaking on the source address persistence, LTM creates a new persistence record as netmask is /32 which makes a new record for each request. As the number of sources increases, the number of records created and saved locally in the persistence table increases which might be an issue. So such a large list of persistence records can become a resource issue for LTM.

To avoid this issue, you can create a custom source address persistence profile and change the mask to (for example: /24) to avoid creating many entries. but you will face another issue, and more users will be identified as coming from the same source.

So based on the above, if you increased the timeout, the entries will be saved for a longer time, and the table will become very large which might be resource intensive based on the number of requests.

I'm not seeing any articles mentioning performance issues when increasing the timeout, but it logically might have an issue because these entries are saved locally on F5, and the more sources access the service with (a long timeout) the more entries will be saved on F5 without clearing the old ones.

Thanks,

1. you can set it to 'undefinite' and the persistence entry will not time out (I'm not aware of any use case of this)

2. No but.. There is no impact because 180s is often unsufficient and we often set it to 30mn to 12 hours or more, but theoretically if you have a huge number of users, the persistence table will get extremely large and this is bad for performance. In this case, you can use cookie persistence or if you have to use source persistence you can specify a shorter prefix length