Technical data

58 Brocade ServerIron ADX Advanced Server Load Balancing Guide

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Other transparent cache switching options

Source MAC address tracking for TCS

If content is not found locally, some cache servers will initiate a connection to the Internet using the

same TCP parameters as the incoming client connection (source IP:source port destination

IP:destination port), which can cause a conflict with the original client connection.

For such situations, ServerIron ADX enables you to track the source MAC address of the incoming

packet. If the source MAC address is that of the cache server, ServerIron ADX TCS will consider this

connection as separate from the conflicting client connection.

To configure source MAC address tracking for TCS, enter the following command as shown:

ServerIronADX(config)#server cache track-src-mac

Syntax: [no] server cache track-src-mac

If a cache server has two interfaces connected to a ServerIron ADX including one for Internet

traffic, the “alias-name” must be configured as shown in the following:

ServerIronADX(config)#server cache-name cs1-dummy 10.1.1.2

ServerIronADX(config-rs-cs1-dummy)#exit

ServerIronADX(config)#server cache-name cs1 10.1.1.1

ServerIronADX(config-rs-cs1)#alias-cache cs1-dummy

ServerIronADX(config-rs-cs1)#

NOTE

The source MAC address tracking feature is now supported for both Layer 4 TCS and Layer 7 TCS.

Configuring source NAT

Normally, when the ServerIron ADX redirects a client’s web request to a cache server, the

ServerIron ADX translates the destination MAC address of a client request into the MAC address of

the cache server. However, the ServerIron ADX does not translate the source or destination IP

addresses in the client’s request.

Generally, in network topologies where the ServerIron ADX and cache server are directly connected

or connected through a Layer 2 switch or bridge, the cache’s response to a client query always

passes back through the ServerIron ADX. The ServerIron ADX uses the cache response to assess

the health of the cache server. When the ServerIron ADX passes a cache response to the client, the

ServerIron ADX assumes the cache server is healthy.

However, if the time since the last packet the ServerIron ADX sent to the cache server and the

cache server’s response increases significantly, or the cache server’s reply never reaches the

ServerIron ADX but instead takes an alternate path to the client, the ServerIron ADX assumes that

the cache server has stopped responding. When this occurs, the ServerIron ADX marks the cache

server FAILED and stops redirecting client queries to the cache server.