Custom Persistance for customers behind Firewalls

Hi , i was wondering if there was any knows ways to get around the following issue.

 

 

we have a VS setup as a HTTP proxy, using source-add persistence which works well for 80% of our customer base.

 

 

However some larger of our customers have their own Firewall's / ISA servers which only presents a single public IP to the BigIP , therefore a whole customer which potential has 2000 PC's behind gets load balanced to a single pool member for a period of time.

 

 

I know when we were on V4 BigIP we have issues with cookie persistence.

 

 

But i was thinking along the lines of setting up the VS with a primary persistence of cookie insert and the the default secondary persistence of source address.

 

 

is there any issue with this ? would that do what i need ? or do I need to create a custom iRule that uses X-forwarding-for?

 

 

 

 

any thoughts on this appreciated

 

Thanks

 

Ian