Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 32)

16 Brocade Virtual ADX Server Load Balancing Guide
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Overview
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The Brocade Virtual ADX switches all subsequent connections to S2 to ensure that the application
session completes successfully.
By default, the concurrent property of a virtual TCP or UDP service port is enabled except for FTP,
Telnet, TFTP, HTTP, and SSL ports.
Remote Servers
The application servers that are a Layer 3 hop away (in other words, in a different subnet that is
separated by router) are identified as remote servers in the Brocade Virtual ADX.
Direct Server Return
DSR (Direct Server Return) configures the Brocade Virtual ADX to instruct real servers to send
client responses directly to the clients instead of sending the responses back through the Brocade
Virtual ADX. As a result, the clients experience faster response times and the Brocade Virtual ADX
is free to support more sessions to serve more clients.
The Brocade Virtual ADX supports both Layer 2 Direct Server Return (L2 DSR) and Layer 3 Direct
Server Return (L3 DSR).
• In an L2 DSR configuration, the Brocade Virtual ADX and the real servers are on the same
subnet.
• In an L3 DSR configuration, the Brocade Virtual ADX and the real servers need not be on the
same subnet; they can be connected through a router.
Understanding L2 DSR
As in standard SLB configurations, an L2 DSR-configured Brocade Virtual ADX sends client
requests addressed to a VIP to a load balanced real server. However, the Brocade Virtual ADX does
not translate the destination IP address in the client’s request from the VIP into the real server’s IP
address as in other SLB configurations. Instead, the Brocade Virtual ADX leaves the destination IP
address unchanged. And the Brocade Virtual ADX also formats the client request packets in such a
way that the real servers respond directly to the clients, instead of sending the responses back
through the Brocade Virtual ADX.
For L2 DSR to work you must configure a loopback interface on each real server and give the
loopback interface the same IP address as the VIP. Because the Brocade Virtual ADX sends the
client traffic to the real server without translating the destination address from the VIP into the real
server's IP address, the real server receives the client traffic addressed to its loopback address
and responds directly to the client.