Web Cache Engine

icon Web Cache Engine

Introduction

If WCCP protocol is enabled on a router and on an interface, the router looks at a outbound IP packet to see if it is destined for TCP port 80. If so, the packet is redirected to a Cache Engine. For this to work, IP must be configured on the interface connected to the Internet, and on the interface connected to the Cache Engine. The latter must be Ethernet or Fast Ethernet.

Although the WCE need not be on a subnet directly connected to its "home" router, it should be close to it to reduce unnecessary network traffic. The home router is specified as part of the configuration of the WCE.

There is a limit of 900 concurrent connections per WCE. This does not translate directly to a certain number of users. See the documentation for discussion of this. Approximately 20 users use up one full-time TCP session. Based on this, one WCE can support 18,000 active users.

Very large scale designs can use multiple levels, with hierarchical operation.

ISP peering points allow two-way Web caching.

Web Cache Engine (WCE) Configuration

The WCE is installed via a console cable. It needs to be told the following:
 
  • IP address
  • Subnet mask
  • Default gateway
  • WCCP home router (often the default gateway as well)
  • New admin password
  • Cache engine name for this WCE
  • Group name for the server farm this WCE is installed in
  • GMT date and time
  • Config register (normally 0)
After completion, record the URL displayed; you'll use it to manage the WCE.

The management interface is self-explanatory. It allows you to view/manage: 

  • Management users and passwords
  • Status of the WCE
  • Password changes
  • Restricted URL's and MIME types (Good / Bad lists)
  • RADIUS authentication
  • Rebooting
  • Flushing the cache
  • Timeout for inter-cache communication
  • DNS
  • Other technical settings

Web Cache Control Protocol

To enable WCCP on the router, configure the router with the following global command:

ip wccp

Optionally, you may specify the redirect access list: only packets that match this list will be redirected. If there is no redirect access list, all web packets will be redirected. Named access lists can be used in IOS 11.2+.

ip wccp redirect-list { number | name }

Then redirect the Internet (or other) interface to redirect web traffic to the WCE.

ip web-cache redirect

The redirection is performed on outbound packets.

To specify which WCE's WCCP redirects to, specify a WCCP group-list:

ip wccp group-list access-list-number

The access list here is a standard access list containing the addresses of WCE's.

To display information about WCCP:

show ip wccp
show ip wccp web-caches
show ip interface

Other related commands:

clear ip wccp
debug ip wccp events
debug ip wccp packets

Other WCE Notes

Benefits

Speed of content delivery: latency is reduced.

Savings on Internet link utilization can be estimated using % of overall Web traffic and % of redundant traffic. Typical Web traffic is 65-85% of all traffic. Redundant traffic is 30-50% of that, depending on the size of the user community. Thus the savings might be 75% Web traffic x 40% redundant = 30% reduction in traffic.

Scaling

Assuming 30K per Web page, the WCE's 24 GB of cache holds about 800,000 pages.

A WCE Cache Farm of 36 servers (containing "cache cows"?) holds multiple WCE's. This scales to over 500,000 users, 28800 concurrent TCP sessions, and 25,000,000 Web pages.

The Web content is spread over the available cache engines, using a hash on the IP address of the destination Web server. The hashing algorithm used leads to expected linear growth. This approach divides the address space into 255 address groups, distributed across the available WCE's.

Hot spot capability -- dynamic load-based distribution -- is anticipated in the future.

Other

Failure is detected because the Cache Engine sends keepalives to the WCCP home router every 10 seconds. If three are missed, the WCE is assumed to no longer be available. In case of failure, the address allocation is evenly redistributed across remaining WCE's, which begins to cache objects from the new addresses. If all WCE's have failed at a farm, the router then just passes TCP port 80 requests through.


Dr. Peter J. Welcher (CCIE #1773, CCSI #94014) is a Senior Consultant with Chesapeake NetCraftsmen. NetCraftsmen is a high-end consulting firm and Cisco Premier Partner dedicated to quality consulting and knowledge transfer. NetCraftsmen has eleven CCIE's (4 of whom are double-CCIE's, R&S and Security). NetCraftsmen has expertise including large network high-availability routing/switching and design, VoIP, QoS, MPLS, network management, security, IP multicast, and other areas. See http://www.netcraftsmen.net for more information about NetCraftsmen. . New articles will be posted under the Articles link. Questions, suggestions for articles, etc. can be sent to This email address is being protected from spambots. You need JavaScript enabled to view it. .

10/25/1998
Copyright (C)  1998,  Peter J. Welcher