Technical data

102 ServerIron ADX Advanced Server Load Balancing Guide
53-1002435-03
Sample configurations
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ServerIronADX(config)# server cache-name cacheserver4 209.157.22.215
ServerIronADX(config-rs-cacheserver4)# exit
ServerIronADX(config)# server cache-name cacheserver5 209.157.22.225
ServerIronADX(config-rs-cacheserver5)# exit
This example assumes that the cache contains the contents requested by the client. However, if
the cache does not contain the requested page, the cache tries to get the page from the live web
site. In this case, the source address for the request is the IP address of the cache server, instead
of the IP address of the client. Moreover, this behavior can result in a loop from the cache server to
the RAS to the ServerIron ADX and back to the cache server.
To prevent this situation from occurring:
• Define the other interface on the cache server as a cache, but do not place the cache in a
cache group.
Policy-based cache failover
In some TCS configurations, the ServerIron ADX is connected to the clients and also to the Internet
through the same router. Moreover, in some cases the router contains a policy to forward HTTP
requests to a next-hop IP address (virtual IP address) if the packet containing the request matches
a filter configured in the router. Cache Failover (CFO) prevents client requests from becoming lost in
a “black hole” when the cache servers are unavailable. When you configure the ServerIron ADX for
CFO, the ServerIron ADX forwards client requests back to the router for forwarding to the Internet.
Thus, clients still receive the requested content even though the cache servers are unavailable.
Normally, cache groups on the ServerIron ADX do not have virtual IP addresses. Instead, the
ServerIron ADX selects a cache server from the cache group that contains the port to which the
router is connected. Within the cache group, the ServerIron ADX uses a hashing algorithm to select
a specific cache server.
NOTE
The virtual servers in SLB use virtual IP addresses, but TCS does not use virtual IP addresses unless
you are using CFO.
To configure CFO, make sure you do the following.
1. Set up the router and aim the policy on the router at the virtual address on the ServerIron ADX
rather than at the address of the cache.
2. Define the cache or caches on the ServerIron ADX and place them into cache group 1.
3. Define the virtual IP address in cache group 1.
4. Define the IP cache policy as a global cache.
NOTE
For CFO, you must define a global policy, not a local policy.
When you add the virtual IP address to the cache group:
• If the cache server to which the ServerIron ADX sends the HTTP traffic has the requested page,
the cache server sends the page back to the client, typically through the ServerIron ADX. (This
is the normal behavior regardless of whether you have added a virtual IP address.)