Depending on your network topology, you can deploy WCCP cluster either with a single router or with multiple routers. Whether connected to a single router or multiple routers, each appliance in the cluster must be connected identically to all routers in use.
In the following diagram, three SD-WAN appliances accelerate the datacenter’s 200 Mbps WAN. The site supports 750 XenApp users.
As shown on the SD-WAN Datasheet, a SD-WAN 3000-100 can support 100 Mbps and 400 users, so a pair of these appliances supports 200 Mbps and 800 users, which satisfies the datacenter’s requirements of a 200 Mbps link and 750 users.
For fault tolerance, however, the WCCP cluster should continue to operate without becoming overloaded if one appliance fails. That can be accomplished by using three appliances when the calculations call for two. This is called the N+1 rule.
Failure is an unusual event, so usually all three appliances are in operation. In this case, each appliance is supporting only 67 Mbps and 250 users, leaving plenty of headroom, and making good use of the fact that the cluster has three times the CPU power and three times the compression history of a single appliance.
Without WCCP clustering, the same level of capacity and fault-tolerance would require a pair of SD-WAN 4000-500 appliances in high availability mode. Only one of these appliances is active at a time.
Using multiple WAN routers is very similar to using a single WAN router. If the previous example is changed to include two 100 Mbps links instead of one 200 Mbps link, the topology changes, but the calculations do not.