ServerIron ADX Global Server Load Balancing Guide 193
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Chapter

2
Global Server Load Balancing for IPv6

Global server load balancing for IPv6 overview

Global Server Load Balancing (GSLB) enables a ServerIron ADX to add intelligence to authoritative
Domain Name System (ADNS) servers by serving as a proxy to these servers and providing optimal
IP addresses to the querying clients. As a DNS proxy, the GSLB ServerIron ADX evaluates the IP
addresses in the DNS replies from the ADNS and places the “best” host address for the client at
the top of the DNS response. The GSLB ServerIron ADX can also directly respond to the DNS
queries in the DNS cache proxy with DNS override mode.
As data centers increasingly move towards migrating some or all of their servers and services to
IPv6, there is an increasing need to perform GSLB for these IPv6 entities in addition to IPv4.
Brocade GSLB ServerIron ADX performs GSLB for both IPv4 (A records) and IPv6 (AAAA records)
and directs the clients to the optimal IP address based on the configured GSLB policies.
In the current implementation, the ServerIron ADX supports global server load balancing and
redundancy for IPv6 addresses in DNS cache proxy with DNS override mode only. In this mode, the
IPv6 addresses for hosts are configured on the ServerIron ADX GSLB controller, which acts as the
authoritative DNS server for the configured zones. The GSLB controller does not have a backend
DNS server. Instead, the GSLB controller intercepts DNS queries and generates the DNS response
by applying GSLB policies on the IPv6 list configured for the hostname.
The GSLB controller ensures that a client always receives a DNS reply for a host site that is the best
choice among the available hosts. Just as with data centers in which the content for a domain can
be serviced by IPv4 and IPv6 servers, a domain on the GSLB ServerIron ADX can have a mix of IPv4
and IPv6 domain IPs. If the client makes an A record query, then the best IPv4 domain IP will be
selected for the client. Similarly, if the client makes a AAAA query, then the best IPv6 domain IP will
be selected for that client.
ServerIron ADX GSLB for IPv6 configuration tasks are covered in four sections within this chapter:
•Basic GSLB for IPv6 configuration: Basic configuration tasks include the configuration of the
GSLB ServerIron ADX and the site ServerIron ADXs to support GSLB of IPv6 addresses. This
includes the configuration of a virtual IP address (VIP) for the ADNS, the configuration of DNS
cache proxy mode with override lists, and the definition of zones and sites on the GSLB
ServerIron ADX. The GSLB protocol must be enabled on the site ServerIron ADX.
•Advanced GSLB for IPv6 configuration: Advanced configuration tasks include the configuration
of GSLB policies and diyr persistence for IPv6 addresses.
•Displaying GSLB for IPv6 configurations: This section describes commands for viewing GSLB
configurations on the ServerIron ADX.
•Troubleshooting GSLB for IPv6 configurations: This section describes steps that may be taken
to troubleshoot GSLB for IPv6 configurations.