Hi,
At the end of the day, this really depends on what platform is doing the redirection, and your IP address plan.
Assume that this your "datacenter" (or central site) where all your servers are located, and you're running WCCP L2-redirect, since you're talking about masking.
But please consult these two links for platform recommendations :
http://products.mcisco.com/c/en/us/products/collateral/routers/wide-area-application-services-waas-software/white_paper_c11-608042.html
https://supportforums.cisco.com/document/133201/wccp-platform-support-overview
With 4 WAEs in the farm, I would go for a mask of "x0f", which is the default in many newer (greenfield) WAAS installations (the old default was 0x1741 giving some strange loadbalancing in many situations).
It will use the last octet of the IP address (src or dst depending upon WCCP group 61/62) as the load balancing determination.
Check this link http://sabotage-networks.blogspot.dk/2012/05/wccp-redirect-acls-and-masks.html
Hope this answers your questions
Best Regards
Finn
