Technical data

Brocade ServerIron ADX Advanced Server Load Balancing Guide 73

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Other transparent cache switching options

Proxy servers with auto-last hop support

TCS also supports certain proxy servers connected to a ServerIron ADX. In this setup, the

ServerIron ADX is configured with Layer 4 TCS with spoof support so that the proxy-to-Internet

server connection is treated as a spoofed connection. However, some proxy servers initiate spoofed

connections using the same client IP address and the same source port. On the ServerIron ADX,

this leads to conflicts with existing client-to-proxy sessions, unless the server cache

track-source-mac command is configured. This command allows the ServerIron ADX to track the

source MAC address of the incoming packet, and mark it as a separate spoofed flow if the source

MAC address belongs to a proxy server. This configuration works for most setups; however, some

proxy servers which use the “auto-last hop” feature can run into the following problem when

connected to a ServerIron ADX running on switch code. Figure 19 shows an example setup of a

proxy server using the “auto-last hop” feature and is configured with the server cache

track-source-mac command:

FIGURE 19 With “auto-last hop” and “server cache track-source-mac” setup

In Figure 19, the following flow occurs:

1. Client sends SYN to the Internet server with Src MAC: A (client MAC), dest MAC: B (Default

Gateway MAC)

2. ServerIron ADX intercepts this SYN, and sends it to the proxy server with Src MAC:A, Dst MAC: C

(proxy server MAC)

3. Proxy server sends SYN to the Internet server back to the ServerIron ADX with Src MAC: C, but

Dst MAC: A. This is called “auto-last hop”, i.e., the traffic is sent back to the destination where

it came from.

4. As a result, the ServerIron ADX sends SYN back to the client with Src MAC: C, Dst MAC: A,

causing traffic failure.

In order to support the setup in Figure 19, configure the ServerIron ADX with the server cache

track-source-mac command with the option spoof-mac.

ServerIronADX(config)#server cache track-source-mac spoof-mac

Syntax: [no] server cache track-source-mac [spoof-mac]