BROCADE IP PRIMER

Chapter 16: Session Persistence and Transparent Cache SwitchingPolicy-based CachingNormally, the ServerIron tries to cache any web site that is requested. Someweb sites, however, should not be cached. Perhaps their site's information istoo dynamic. Whatever the case, you can use Policy-based Caching to decidewhich web requests to always forward to the Internet.This is a two step process. The first step is to define the filters. You want todefine which destination IP addresses should not be retrieved from cache.Here is an example:SLB-ServerIron#conf tSLB-ServerIron(config)#ip filter 1 deny any 123.1.2.3255.255.255.255 tcp eq 80SLB-ServerIron(config)#ip filter 2 deny any 213.2.3.4255.255.255.255 tcp eq 80SLB-ServerIron(config)#ip filter 1024 permit any anyDon't let the “deny” fool you. These are not ACLs. They are filters. A “deny” heremeans that the ServerIron will never attempt to pass requests for these serversto the cache servers. It will always forward them to the Internet. In thisexample, we have set aside the web servers at “123.1.2.3” and “213.2.3.4.”Web requests to these servers should always be forwarded to the Internet(never to the cache servers). Notice that we did not use a wildcard mask, but a1s mask (like the subnet mask). Here, a mask of all 1s means “this IP addressand only this IP address.”Finally, the last line (which is customarily assigned filter number 1024; the lastfilter) has a global “permit any any.” This means that all other destinationsbeside these two servers should be forwarded to the cache servers wheneverpossible. This is important. Like ACLs, filters take on an implicit “deny all” atthe end unless a “permit” is defined. If we leave that last line off, all webrequests are forwarded to the Internet, and the cache servers would never beused. This last line doesn't have to be filter 1024 (it could have been “3,” inour example), but it's a good practice. It leaves you free to add additional filtersif necessary, without having to worry about that last line.I said there were two steps. The second step is to apply these policies to thecache servers. This is done with the keyword “filter-match,” and it is done inthe cache servers' config:SLB-ServerIron#conf tSLB-ServerIron(config)#server cache-name Cache1 10.2.3.4SLB-ServerIron(config-rs-Cache1)#filter-matchNow the policy is applied. The ServerIron knows not to forward web requestsfor 123.1.2.3 and 213.2.3.4 to the cache servers (but to forward all otherdestinations).368 Brocade IP Primer