Brocade Communications Systems 12.4.00 manual Active RTT gathering and high availability support

Round-trip times 1

If both the ICMP and DNS fast-aging commands are enabled on the Site ServerIron ADX, then failure of either ICMP or DNS probes will quickly age out LDNS prefixes from the active RTT cache. Typically you should enable only one of these commands. Follow the guidelines below to determine which command to enable:

•If you want DNS RTT measurements to be the primary source of RTT and DNS prober is enabled on the Site ServerIron ADX, then enable the gslb agent-fast-age-dns-failcommand if LDNS prefixes need to quickly age out if a DNS probe fails.

•If you want ICMP RTT measurements to be the only source of RTT and DNS prober is not enabled on the Site ServerIron ADX, then enable the gslb agent-fast-age-icmp-failcommand if LDNS prefixes need to quickly age out if an ICMP probe fails.

•If you want the LDNS prefix to be aged out when either DNS or ICMP prober fails, then enable both commands on the Site ServerIron ADX.

•If no fast aging is desired, then do not enter either of the commands.

Active RTT gathering and high availability support

Brocade GSLB with active RTT gathering will operate in all High Availability (HA) configurations supported in earlier software releases.

To ensure that active RTT gathering is synchronized between devices that are in an HA configuration, GSLB active RTT gathering does the following:

•If two GSLB ServerIron ADXs are in an HA configuration and both have active RTT gathering enabled, then each active RTT gathering Site ServerIron ADX reports the actively gathered RTT information to both the GSLB ServerIron ADXs. This ensures that the standby GSLB ServerIron ADX receives the actively gathered RTT information and is able to immediately use this information if the primary GSLB ServerIron ADX fails over.

•If two Site ServerIron ADXs are in an HA configuration and have active RTT gathering enabled, then the GSLB ServerIron ADX sends the active RTT gathering request with the list of LDNS hosts that are to be probed to both the Site ServerIron ADXs. Each of the Site ServerIron ADXs in the HA configuration actively gathers RTT measurements from the LDNS hosts in the list and reports information to the GSLB ServerIron ADX. This ensures that the GSLB ServerIron ADX receives RTT information for both the Site ServerIron ADXs. If the primary Site ServerIron ADX fails over and the standby Site ServerIron ADX takes over, the GSLB ServerIron ADX will already have the RTT information for the standby Site ServerIron ADX. The GSLB ServerIron ADX will be able to immediately select the best IP address based on the information it has.

ServerIron ADX Global Server Load Balancing Guide	151
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