GTM persistency options for large LDNS clients

Is there any kind of consensus on how to attempt to manage large, disparate LDNS networks that may end up coming out of a /16 or even a /10 CIDR block?

 

 

I've got a e-commerce site that needs to service the world, but of course it's got the traditional problems: persistency is required to the datacenter (and server) where the transaction originated.

 

 

Examples of large LDNS networks would include:

 

 

U.S. Postal Service

 

Cox Communications

 

Comcast

 

AT&T

 

Verizon

 

AOL

 

 

I've tried a number of things including increasing the pool TTL so hopefully they can complete their transaction before the LDNS re-requests, as well as playing around with CIDR masking up to about /20.

 

 

The solution in place gets about 99% of the transactions through, but some fail due to getting a pool address from a different datacenter than when they started in mid-transaction.

 

 

In the past I've written iRules to send traffic to a pool that's set to Global Availability instead of one that's load balanced based on the source LDNS, but having to track down all the ARIN address space of say, AOL or Comcast proved to be too much to keep up with, reasonably. And by the time you put that many clients in the a GA pool why not make the whole app GA (which isn't an option).

 

 

Are there any better solutions other than cranking the CIDR down further and increasing the TTL? Unfortunately this is a GTM-only solution so I don't have access to something more advanced, like LTM iRules with cookies or something similar.

 

 

Thanks,

 

 

Cooper Van Valkenburgh