Technical data

Brocade ServerIron ADX Advanced Server Load Balancing Guide 53
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Other transparent cache switching options
2
NOTE
The resilient hashing mechanism supports High Availability (HA).
NOTE
The resilient hashing mechanism supports IPv6.
Cache route optimization
Typically the ServerIron ADX sits between a border access router (BAR) and a remote access server
(RAS) where the BAR connects to the Internet/intranet. The RAS forwards the client HTTP traffic to
the ServerIron ADX, which redirects the traffic to the cache servers. When a border router is
configured as the default router for the cache servers, all traffic sent towards the browsing clients
behind the RAS must first go to the BAR.
At Layer 3, the cache server sends its response to the IP address of the client (or to the ServerIron
ADX if source NAT is enabled on the ServerIron ADX). However, at Layer 2, the cache server sends
its response to the MAC address of its default gateway. In configurations where the default gateway
is the BAR, this traffic pattern can cause significant (and unnecessary) BAR performance
degradation and poor response time as perceived by the clients.
Cache route optimization (CRO) sends traffic from a cache server toward the RAS. When you enable
the feature, the ServerIron ADX uses information in its Layer 4 session table and its traffic pattern
recognition capabilities to redirect the traffic directly toward the clients instead of sending the
traffic needlessly to the BAR.
Cache route optimization is disabled by default.
Enabling cache route optimization
Cache route optimization is useful for situations in which a cache server’s default gateway is the
border access router (BAR) that goes to the Internet, instead of the remote access server (RAS) that
goes to the HTTP clients.
When you enable cache route optimization, the ServerIron ADX intelligently sends cache responses
directly to the RAS at Layer 2 instead of sending them to the BAR for switching back through the
ServerIron ADX to the RAS.
Cache route optimization is enabled on a ServerIron ADX as shown.
ServerIron(config)#server cache router-offload
Syntax: [no] server cache router-offload
NOTE
FTP is not supported when cache-router-offload is enabled.
Cache route optimization example
Cache route optimization (CRO) solves a typical network topology dilemma, in which a cache
server’s default gateway is not the most direct route to the client. Figure 10 shows an example of a
network with this topology.