Web Cache Communication Protocol

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 255 service groups (0-254)
• Adds MD5 shared secret security

• Accelerator or Engine is a WCCP client
  • Registers WCCP services (0-254) 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 (0-254)
  • 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

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

• Redirect list allows router to permit/deny traffic to intercept
• Two methods of redirection:
  • WCCP L2: Local subnet only, little overhead. Rewrites packet MAC address to that of the local Engine
  • WCCP GRE: Any IP-Subnet, more overhead. Creates tunnel from router to local or remote Engine.

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

Whilst originally designed for Cisco's Content Cache appliance they have since added support to other products, including:

• ASR 1000 Routers ^[1]
• Application & Content Networking System (ACNS)
• Wide Area Application Services (WAAS)
• ASA/PIX Firewalls
• Some IOS versions
• IronPort S-Series Web Security Appliance
• Nexus 7000 Switches

Other vendors have also implemented WCCP support into their products, as it allows clustering and transparent deployment on networks using Cisco routers/switches without additional hardware. WCCP is of particular use to vendors of web cache/proxy/security appliances for redirection of web traffic. Please note that some vendors did not follow the standards when implementing WCCP and this could result in intercompatibility problems.

A list includes:

• Cisco
  • Section WCCP Network Caching in the Cisco DocWiki (formerly known as the "Internetworking Technology Handbook")
  • Section Configuring Web Cache Services Using WCCP in the "Cisco IOS Configuration Fundamentals Configuration Guide, Release 12.2"
  • Section WCCPv2 and WCCP Enhancements in the feature guide for "Cisco IOS Software Releases 12.0 S"
• Configure WCCP on your Cisco IOS router on TechRepublic
• Web Cache Communication Protocol V2, revision 1 on IETF Web Site
• How to set up WCCP on your Barracuda Web Filter in Barracuda Networks Knowledgebase