Brocade Communications Systems ServerIron ADX 12.4.00 Service Manual Page 60

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48 ServerIron ADX Advanced Server Load Balancing Guide
53-1002435-01
Other TCS options
2
You can reduce the burden on the BAR by enabling CRO. This feature configures the ServerIron
ADX to use the information in its Layer 4 session table to recognize that the return traffic actually
should go to the RAS instead of the BAR, and send the return traffic directly to the RAS. Thus, the
return traffic does not needlessly add overhead to the BAR.
FIGURE 10 Cache route optimization
To enable CRO for this configuration, enter the following command:
ServerIronADX(config)# server cache-router-offload
Why ICMP Redirects Do Not Solve the Problem
The ServerIron ADX redirects HTTP traffic destined for the Internet to the cache server. When the
cache server responds to the client, it does so by sending its packets to its default gateway
because the users are not in the same subnet as the cache server. However, at Layer 3, the packet
is addressed to a client that is actually accessible through the RAS. The BAR knows the proper next
hop router is the RAS, through a routing protocol, and retransmits the packet to the RAS, at Layer 2.
The RAS forwards the packet to the client. Thus every packet to every client must go to the BAR
and then be retransmitted. The BAR port is already carrying all the fetch and refresh traffic from
that cache and this additional traffic can overload it.
Internet
www.stockquotes.com
1.0.0.2
www.oldnews.com
1.0.0.1
www.livenews.com
1.0.0.3
Web servers
Border Access
Router (BAR)
e18 (output port)
e17
Remote Access
Server (RAS)
Web Queries
208.95.6.3
208.95.7.3
208.95.8.3
Cache server3
209.157.22.205
Cache server4
209.157.22.215
Cache server5
209.157.22.225
Each cache server has a
default route to the BAR,
which must send the traffic
back through the ServerIron
to the RAS.
The Cache Router Optimization
feature configures the ServerIron
to send the return traffic directly
to the RAS.
SI
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