Brocade Communications Systems ServerIron ADX 12.4.00 Service Manual download pdf (Page 47)

ServerIron ADX Advanced Server Load Balancing Guide 35

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TCS Overview

The cache server determines how the web query will be handled by pulling from its local

information stores and facilitating that information with external web queries on the WAN, as

needed, to complete the query.

The ServerIron ADX provides the detection and switching of those HTTP packets forwarded from the

cache server. This process is known as “transparent” cache switching because it is transparent to

the end user. The end user continues to see the web site pages as expected in answer to his or her

query and is unaware that the access point to the information is through the cache server.

Additionally, because TCS works with the default settings of web browsers, no configuration

changes are required on the client station, which further adds to the transparency of the feature.

Response to cache server failures

Web cache servers are grouped with other cache servers to provide for automatic recovery from a

failed or otherwise out-of-service web cache server. The ServerIron ADX monitors the availability of

the cache servers in the group. If a web cache server failure occurs, the switch detects the failure

and directs subsequent requests to the next available cache server or forwards the request directly

to the WAN link. You can gain further reliability by using redundant ServerIron ADXs, thereby

eliminating any single point of failure in the server group network path.

Stateful caching

Stateful caching provides the following services:

• Minimization of route flap problems.

• Graceful shutdown of transparent cache servers.

• Ability to set maximum connections allowed for a cache server.

• Use of access list to control caching based on source and destination addresses.

• Advanced statistics for TCS.

In stateful TCS, the ServerIron ADX creates session table entries for the client connections

redirected to cache servers. The ServerIron ADX uses the return traffic as one means to assess the

health of a cache server.

Minimization of route flap problems

When a route change causes web query traffic to be moved from an non-cached path to a cached

path, no TCS is performed on the active connections.

NOTE

When the opposite transition occurs— web query traffic moving from a cached to non-cached path

— the ServerIron ADX takes no action because the traffic is no longer visible to the ServerIron ADX.

Configurable maximum connections for cache server

You can set the maximum number of connections that a cache server will accept. By setting a limit,

you can avoid a condition where the capacity threshold of a cache server is exceeded.

When a server reaches the maximum defined connection threshold, an SNMP trap is sent. When

all the cache servers in a cache group reach the maximum connection threshold, the ServerIron

ADX sends the client requests to the Internet.

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Brocade Communications Systems ServerIron ADX 12.4.00 Service Manual Page 47