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ciscozest_30697's avatar
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Jun 24, 2018

LTM Source Address Persistence: Prefix Length Guideline

Hi all. I would like to understand the impact of using source address persistence on LTM module. By default is using /32 prefix length. I am thinking of changing this to /24 to reduce big ip persistence table/ to save LTM memory usage. Are there any guidelines to change the prefix length based on number of connections/ sessions? I am using VE platform with 2vCPU / 4GB RAM under ESXi 6.5. Thank you


2 Replies

  • Hello ciscozest!


    Never heard of it. As you said, I think the biggest impact could be in your application. For the VE it would be - if any - a better impact since the table would go down.


    Just take make sure that in this /24 there's no users coming from behind a proxy/nat or something... You could potentially balance a lot to a specific node/pool member.




  • What you need to make that decision is a statistical analysis over time (some multiple of your source IP persistence period) of incoming client IP addresses to your application. Then you can determine if any single /24 is going to cause excessive connection pinning to a pool member.