Brocade Communications Systems ServerIron ADX 12.4.00 - Manual (Page 116)

104 ServerIron ADX Global Server Load Balancing Guide
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Enabling DNS request logging
1
BP support as GSLB agent
If the ServerIron ADX is used as a GSLB agent, the BP synchronizes RTT information collected from
clients that make TCP SLB connections to the ServerIron ADX, to the MP. The MP communicates
this RTT information to all collectors with which it opened TCP port 182 connections.
Note that the agent needs to be serving TCP SLB connections in order to collect RTT samples from
client networks. This is because the ServerIron ADX bases the RTT calculation on the TCP 3-way
handshake mechanism during connection establishment. If the agent is running only UDP
applications, there will be no RTT updates from that agent.
Also note that the RTT is not application specific. All TCP connections are used to sample RTTs.
Distributed health checks for GSLB
The GSLB ServerIron ADX evaluates each IP address in the DNS reply based on a set of criteria.
Depending on the results of this evaluation, the GSLB ServerIron ADX reorders the list to place the
“best” IP address on the top of the list. Usually the GSLB ServerIron ADX uses a server’s health as
one of the most important criteria to evaluate the server IP addresses in a DNS reply. The GSLB
distributed health check feature distributes the health checking task, currently carried out by the
GSLB ServerIron ADX, to the site ServerIron ADXs.
A ServerIron ADX has the GSLB distributed health check feature enabled by default. If the GSLB
ServerIron ADX as well as the site ServerIron ADX support the GSLB distributed health check
feature, the site ServerIron ADX will periodically report the health check status information of the
host servers being load balanced by it, to the GSLB ServerIron ADX. GSLB ServerIron ADX will no
longer need to maintain health checks on these host servers being load balanced by this site
ServerIron ADX. Thus the GSLB distributed health check feature helps offload the task of health
checking from the GSLB ServerIron ADX and distributes it to the peer site ServerIron ADXs that
support the GSLB distributed health check feature.
The distributed health check feature provides the following benefits:
• Reduction of GSLB ServerIron ADX load
• Reduction of GSLB health check traffic
• Increased scalability due to distribution of health checking task to site ServerIron ADXs
• Ability to configure and modify the interval at which site ServerIron ADXs report the health
check information to the GSLB ServerIron ADX.
In addition to this, a distributed health check GSLB ServerIron ADX will inter-operate with a
non-distributed health check site ServerIron ADX and a distributed health check site ServerIron
ADX will also be compatible with a non-distributed health check GSLB ServerIron ADX (no additional
configuration required). Some configuration is required in the first case but not the latter case.
Refer to
“Disabling the distributed health check feature for an individual site ServerIron ADX” on
page 105 and “Disabling or re-enabling distributed health check” on page 106.
You are not required to use the same health check mode (distributed or centralized) on all
ServerIron ADXs in the GSLB configuration. You can transition the distributed health check
mechanism into your GSLB network, one site or even one site ServerIron ADX at a time, if desired.
Alternatively, if you want to use the distributed health check feature for all ServerIron ADXs, all you
need to do is upgrade all of them to 08.1.00S release.