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So do you a scenario something like this?

         clients
            |
    9.4 external LTM pair
            |
iPlanet reverse proxy (or proxies?)
            |
   9.4 internal LTM pair
            |
       web servers

If you connect to the web servers through the iPlanet proxy and the internal LTM pair, does the web app work correctly? If not, that would be the first issue to address. If that does work, then the next question is: Is there more than one iPlanet proxy actively handling connections? If there is only one active iPlanet proxy, you shouldn't need to make any changes to the external pair of LTM's. If there are multiple iPlanet proxies, do you need to persist clients to the same iPlanet cluster member in order for the app to work? If so, try adding a persistence profile to the VIP on the external LTM pair.

If the web app doesn't work through the iPlanet proxy, try disabling all but one node in the internal LTM pool. If the web app then works, you can be fairly certain it is a persistence issue.

Try adding a second node to the web server pool on the internal LTM pair to test the persistence. You could then try inserting a custom HTTP header on the external LTM pair with the client IP address or some other unique per-client token. You could then persist off of that token using a rule on the internal pair.

If I'm off base, please clarify. Else, let me know if you have any questions on these suggestions.

Aaron