Setting up transparent proxying with an L4 or L7 switch includes specifying in the switch configuration each NetCache appliance to which the switch can redirect traffic. Based on your configuration of the switch, the switch automatically distributes requests across the NetCache appliances. The following illustration shows a typical forward proxy deployment with a L4 switch distributing HTTP requests over three NetCache appliances.
If a NetCache appliance that is identified in the switch configuration is unavailable, the switch distributes the requests over the available appliances.
Each time you add a proxy-cache server to your network, you must reconfigure the switch with information about the new proxy-cache server. This reconfiguration is not necessary with a WCCP router.
The hashing function on a switch can be set up to distribute requests over NetCache appliances based on either of the following:
Typically, you will want to achieve an even distribution of requests across your NetCache appliances.
When determining how distribution based on IP address will be set up on a switch, consider the most efficient method for the mode in which you are running your NetCache appliance, as the following table shows.
The details about the two distribution methods for IP address hashing are described in the following paragraphs.
When users send requests to arbitrary Internet servers (that is, requests are sent to many destinations), distribution on destination IP address provides the most equal distribution over multiple NetCache appliances that are running as forward proxies.
Requests for objects from the same origin server are sent to the same proxy-cache server, thereby minimizing duplication of objects among proxy-cache servers. If a proxy-cache server becomes unavailable, another proxy-cache server temporarily handles requests for the unavailable proxy-cache server, thereby caching objects for origin servers for which it is not ordinarily responsible. When the unavailable proxy-cache server is again available, it takes over responsibility for handling requests for the same origin servers that it handled previously.
If you are deploying an accelerator, configuring the switch to partition requests based on source IP address provides the best distribution over your NetCache appliances. With request distribution based on source IP address, each appliance receives a portion of the load of client requests. The problem with partitioning requests based on destination IP address is this: if the NetCache appliance is accelerating only one origin server, all requests will be sent to one NetCache appliance because the destination address would be the same for all requests. (The hashing function sends requests for the same destination IP address to the same NetCache appliance.) Even if your NetCache appliance is accelerating a few origin servers, the variation in destination IP addresses would be limited.
When partitioning is based on source IP address, objects might be duplicated among your accelerators because multiple NetCache appliances would be fetching the same objects. However, the hit rate with an accelerator is higher than with a forward proxy. Therefore, duplication of objects is not a concern, as it is with a forward proxy. The reason is that the Web server or streaming server that NetCache accelerates has a limited amount of data, as compared to the World Wide Web, which has nearly an infinite amount of data. With an accelerator, it is likely that many users will send requests for the same data from the Web server or streaming server.
See Strategies for client access to an accelerator for an example of an accelerator deployment with a switch or WCCP router.
Some L7 switches allow for request distribution based on URL. The L7 switch examines the request and determines whether the object is cacheable. This capability enables you to set up your switch so that requests for obviously uncacheable objects, such as URLs for CGI, bypass the NetCache appliance. Noncacheable objects are then obtained directly from an origin server.
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Part No. 210-00372
File: access6.htm
Last updated: 11/13/02 18:10:53