WCCPv2 Load Distribution WCCPv2 can be used to adjust the load being offered to individual content engines to provide an effective use of the available resources while helping to ensure high quality of service (QoS) to the clients. WCCPv2 allows the designated content engine to adjust the load on a particular content engine and balance the load across the content engines in a cluster. WCCPv2 uses three techniques to perform load distribution: • Hot spot handling: Allows an individual hash bucket to be distributed across all the content engines. Prior to WCCPv2, information from one hash bucket could go to only one content engine. • Load balancing:
Allows the set of hash buckets assigned to a content engine to be adjusted so that the load can be shifted from an overwhelmed content engine to other members that have available capacity. • Load shedding: Enables the switch to selectively redirect the load to avoid exceeding the capacity of a content engine. The use of these hashing parameters prevents one content engine from being overloaded and reduces the potential for bottlenecking. WCCP Bypass Packets WCCP intercepts IP packets and redirects those packets to a destination other than the destination that is specified in the IP header.
Typically the packets are redirected from a web server on the Internet to a web cache that is local to the destination. Occasionally a web cache cannot manage the redirected packets appropriately and returns the packets unchanged to the originating device. These packets are called bypass packets and are returned to the originating device using Layer 2 forwarding without encapsulation (L2). The device decapsulates and forwards the packets normally. The VRF associated with the ingress interface (or the global table if there is no VRF associated) is used to route the packet to the destination.
WCCP Closed Services and Open Services In applications where packets are intercepted and redirected by a Cisco switch or a router to external WCCP client devices, it may be necessary to block the packets for the application when a WCCP client device is not available. This blocking is achieved by configuring a WCCP closed service. When a WCCP service is configured as closed, the packets that fulfill the services, but do not have an active client device, are discarded. By default, WCCP operates as an open service, wherein communication between clients and servers proceeds normally in the absence of an intermediary device.
The ip wccp service-list command can be used for both closed-mode and open-mode services. Use the service-list keyword and service-access-list argument to register an application protocol type or port number. Use the mode keyword to select an open or closed service. WCCP Outbound ACL Check When WCCP is enabled for redirection on an ingress interface, the packets are redirected by WCCP and instead egress on an interface other than the destination that is specified in the IP header. The packets are still subject to ACLs configured on the ingress interface. However, redirection can cause the packets to bypass the ACL configured on the original egress interface.
Packets that would have been dropped because of the ACL configured on the original egress interface can be sent out on the redirect egress interface, which poses Configuring WCCP WCCPv2 Load Distribution Configuring WCCP 6