230 ServerIron ADX Global Server Load Balancing Guide
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Advanced GSLB configuration for IPv6
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A site must pass all applicable Layer 4 and Layer 7 health checks to avoid being removed.
NOTE
If all the sites fail their health checks, resulting in all the sites being rejected by the GSLB ServerIron
ADX, the ServerIron ADX sends the DNS reply unchanged to the client.
The GSLB default behavior is as follows:
•In DNS proxy, the entire list of IP addresses is sent back to the client with the best IP
address selected by the GSLB controller at the top of the list. This best IP is selected in
accordance with the GSLB policy. An administrator typically configures an active-only
policy, because the LDNS may cache this response for TTL time and may round robin the
IPs in this list in some cases.
•Health check in the GSLB policy is disabled. Typically administrators will not disable health
check if they are using an active-only policy.
•An active-only policy applies only to the remaining IP addresses in the IP list, not the best
one. An administrator should enable health check for best IP selection to ensure that best
IP is healthy.
To configure the ServerIron ADX to remove IP addresses from DNS replies when those addresses
fail a health check, enter the following commands:
ServerIronADX(config)# gslb policy
ServerIronADX(config-gslb-policy)# dns active-only
Syntax: [no] dns active-only

Configuring a best-only policy

The GSLB policy places the best IP address selected by the GSLB policy at the top of the list.
Use the dns best-only command to configure the ServerIron ADX to return only the best IP address
in the DNS response.
NOTE
If the GSLB policy does not result in the selection of a “best” address, the DNS reply can still contain
multiple addresses.
To configure the GSLB ServerIron ADX to remove all addresses except the best address from the
DNS replies, enter the following commands:
ServerIronADX(config)# gslb policy
ServerIronADX(config-gslb-policy)# dns best-only
Syntax: [no] dns best-only
GSLB of ANY queries
DNS supports many different record types including IPv4 address records (A records), IPv6 address
records (AAAA records), Name Server records (NS records), Mail Exchange (MX records), Canonical
Name records (CNAME records) and so on. DNS also supports a special query type called "ANY".
If a client sends an ANY query, the GSLB ServerIron ADX applies the GSLB policy to the IP
addresses configured for that domain in its IP list.