Web Cache Communication Protocol

Web Cache Communication Protocol (WCCP) is a Cisco-developed content-routing protocol that provides a mechanism to redirect traffic flows in real-time. It has built-in load balancing, scaling, fault tolerance, and service-assurance (failsafe) mechanisms. Cisco IOS Release 12.1 and later releases allow the use of either Version 1 (WCCPv1) or Version 2 (WCCPv2) of the protocol.

WCCP allows utilization of Cisco Cache Engines (or other caches running WCCP) to localize web traffic patterns in the network, enabling content requests to be fulfilled locally. Traffic localization reduces transmission costs and download time.

Protocol Versions

WCCPv1
* Only a single router services a cluster of systems
* Supports HTTP (TCP port 80) traffic flows only
* Provides generic routing encapsulation (GRE) to prevent packet modification
* Routers and cache engines communicate to each other via a control channel based on UDP port 2048

WCCPv2
* Allows for use across up to 32 routers (WCCP servers)
* Supports up to 32 engines/accelerators (WCCP clients)
* Supports any IP protocol including any TCP or UDP
* Supports up to 256 service groups (0-255)
* Adds MD5 shared secret security
* Primary WCCP functions

Registration

* Accelerator or Engine is a WCCP client
** Registers WCCP services (0-255) with “Here I Am” if application is operational
** Registration announces WCCP client on service group, provides availability notification, requests interesting traffic
** Transmits “Here I Am” every 10 seconds
** Lead WCCP client (lowest IP address) instructs routers on protocol/port, assignment, forwarding, and return methods
* Router is a WCCP server
** Accepts service group registration (0-255)
** Acknowledges “Here I Am” with “I See You”
** Waits 30 (3x10) seconds before declaring engine failed
** Announce engines to other engines
** Router id is highest interface IP or highest loopback IP if one exists
** Redirects traffic to engine

Assignment

* Selects an engine in the cluster
* Hash 256 buckets
* Mask 128 buckets represented by 7 bit mask of the source or destionation IP/Port

Redirect from Router to Cache Engine

* WCCP GRE redirect creates tunnel from router to local or remote Engine
* WCCP L2 redirect rewrites packet MAC address to that of the local Engine
* Redirect list allows router to permit/deny traffic to intercept

Return from Cache Engine to Router

* WCCP GRE return
* WCCP L2 return
* Engine can optionally return traffic any other way including routing

External links

* [http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a008030c778.html Configuring Web Cache Services Using WCCP] on Cisco's Web site
* [http://articles.techrepublic.com.com/5100-1035_11-6175637.html Configure WCCP on your Cisco IOS router] on TechRepublic
* [http://tools.ietf.org/id/draft-wilson-wrec-wccp-v2-01.txt Web Cache Communication Protocol V2.0] on IETF Web Site
* [http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/12s_wccp.html] WCCP Enhancements on Cisco's site