WCCP load balancing mechanism load balance the Hash or Mask table/bucket rather than balancing the actual traffic itself.
The default balancing will distribute the Hash or Mask table/bucket evenly throughout the Proxy within the WCCP pool , depending on the value used to hash or mask
An Example with Mask
Three Proxy with Mask Assignment, proxy with the highest IP will take the balanced out Mask table as 64/3=21.33 and mask need to be exact non decimal number
Proxy 1 - 21 mask table
Proxy 2 - 21 mask table
Proxy 3 - 21+1=22 mask table
This for example may resulting in
Proxy 1 - assigned with mask table 0 until 20
Proxy 2 - assigned with mask table 21 until 41
Proxy 3 - assigned with mask table 42- 63
refer to FAQ1452 or FAQ1453 for detail on more detail or example of WCCP Mask/Mask distribution works
Router will use the mask table above to decide which traffic would receive certain traffic which is again depend on what mask scheme used (can be source ip, source port, destination IP or destination port)
Typical Cisco command which will reveal the Mask distribution taking effect on Router
Router#sh ip wccp <servicegroup> detail
On ProxySG, the following command can be run on any Proxy within the WCCP pool
ProxySG#sh wccp statistics
Well balanced session aware user traffic is not achievable with WCCP method of balancing. Router decide on which destination proxy in the WCCP pool would received a traffic based on which on result of the Mask/Hash computation and redirect the traffic to the proxy which are assigned with the mask/hash table.
However there are few workaround/tweak which can be used to help shape up the traffic in a better distribution
This include hard coding certain "weight" value for each ProxySG in the pool based on the amount of load observed for certain duration, refer to SGOS 5.5 WCCP Reference Guide document and "Load Balancing Weights" for more detail
If there is a "hotspot" on any of the table, the host spot can be moved to an alternate hash table but this will not result in a well balanced user traffic. Refer to the following WCCP guideSGOS 5.5 WCCP Reference Guide document and refer to section "Hotspot Detection" for more details
Changing the existing Masking or Hashing value can also be performed, kindly refer to SGOS 5.5 WCCP Reference Guide to get some idea on Masking or Hashing option available.