Technical data

ServerIron ADX Advanced Server Load Balancing Guide 51
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Other transparent cache switching options
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Because this scheme works at the MAC layer, it is compatible with all routing protocols. Moreover,
because the scheme is session specific, it can handle any number or RAS. When a session is
terminated, the table entry is deleted and so is the “optimization”. Thus changes in the network at
Layer 3 are immediately implemented.
Enabling destination NAT
By default, 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 IP address of
the request to the cache server’s IP address. Instead, the ServerIron ADX leaves the destination IP
address untranslated.
This behavior assumes that the cache server is operating in promiscuous mode, which allows the
cache server to receive requests for any IP address so long as the MAC address in the request is
the cache server’s. This behavior works well in most caching environments. However, if your cache
server requires that the client traffic arrive in directed IP unicast packets, you can enable
destination NAT.
NOTE
This option is rarely used. If your cache server operates in promiscuous mode, you probably do not
need to enable destination NAT. Otherwise, enable destination NAT. Consult your cache server
documentation if you are unsure whether you need to enable destination NAT.
To enable destination NAT, enter commands such as the following:
ServerIronADX(config)# server cache-name server1
ServerIronADX(config-rs-server1)# dest-nat
Syntax: dest-nat
Destination NAT is disabled by default.
NOTE
FTP is not supported when destination NAT is enabled.
Destination NAT for TCS
If the cache server is remote (not directly connected to the ServerIron ADX), or is running in proxy
mode (client connection is terminated completely from the back-end Internet connection),
destination NAT can be configured for TCS.
When destination NAT is enabled under a cache server, the destination IP of client TCS traffic
(client-to-Internet) is translated to that of the cache server (client-to-cache). The cache server then
serves the web content from its cache, if available. If content is not available locally, the cache
server will request content from the original destination (embedded in the HTTP host header).
When destination NAT is configured under a cache group, the destination IP of TCS traffic to all
cache servers under this cache group is translated to a selected cache server's IP address. This is
applicable for a remote cache server or when a cache server is running in proxy mode (not
transparent mode).