Brocade Communications Systems 12.4.00 manual Disabling or re-enabling the Flashback metric

1 Host-level policies for site selection

Some of the DNS parameters are not configurable in the host-level GSLB policy. These parameters include:

•dns cache-proxy: Enables the ServerIron ADX to act as a proxy for a DNS server, by responding directly to the client queries without forwarding them to the DNS server

•dns check-interval: Changes the refresh interval for DNS queries to refresh verify zone and host information. The GSLB ServerIron ADX sends the queries to the DNS for which it is configured to be a proxy.

•dns cname-detect:Enables the ServerIron ADX to apply GSLB to CNAME records.

•dns override: Replaces the IP address in the DNS reply with the IP address you configure for the proxy server.

•dns transparent-intercept: Enables the DNS transparent intercept feature.

•dns ttl: Specifies the value to which the GSLB ServerIron ADX changes the TTL of each DNS record contained in DNS replies received from the DNS for which the ServerIron ADX is a proxy.

The GSLB ServerIron ADX will use these DNS parameters from the global GSLB policy for the host-level GSLB policy.

Disabling or re-enabling the Flashback metric

The Flashback metric indicates how quickly the GSLB ServerIron ADX receives Layer 4-7 health check results. This metric is enabled by default, which means the GSLB ServerIron ADX uses this metric when evaluating the sites in a DNS reply to choose the best site.

To disable this metric, enter the following command.

ServerIronADX(config)# gslb-host-policy abc

ServerIronADX(config-gslb-host-policy-abc)# no flashback

To re-enable this metric, enter the following command.

ServerIronADX(config)# gslb-host-policy abc

ServerIronADX(config-gslb-host-policy-abc)# flashback

Syntax: [no] flashback

NOTE

When both the Health Check metric and the Flashback metric are disabled for the host-level GSLB policy, the GSLB ServerIron ADX will not perform any Layer 4 or Layer 7 health checks for the hosts/zones to which this policy applies.

Modifying Flashback tolerance

You can modify the following Flashback parameters:

•Application tolerance

•TCP tolerance

The GSLB ServerIron ADX uses a tolerance value when comparing the Flashback speeds of different sites. The tolerance value specifies the percentage by which the Flashback speeds of the two sites must differ in order for the ServerIron ADX to choose one over the other. The default Flashback tolerance is 10%. Thus, if the Flashback speeds of two sites are within 10% of one another, the ServerIron ADX considers the sites to be equal. However, if the speeds differ by more than 10%, the ServerIron ADX prefers the site with the lower Flashback speed.

Flashback speeds are measured at Layer 4 for all TCP/UDP ports. For the application ports known to the ServerIron ADX, the Flashback speed of the application is also measured.

120	ServerIron ADX Global Server Load Balancing Guide
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