A topology rule maps a client IP address to a DNS Traffic Control (DTC) pool or server. To use Topology as the load balancing method for a pool or an LBDN, you must define a topology ruleset containing at least one rule. The rulesets are configured globally. When the DNS Traffic Control returns a response, it evaluates the list of rules in the topology ruleset in order and uses the first match with an available destination. The method fails if there are no matches.
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Limitations of Configuring Topology Rules and Rulesets
Based on the destination type of the DTC Topology ruleset settings, you can set the NOERR/NODATA or the NXDOMAIN response for a new DTC Topology rule. However, you cannot choose the destination DTC Pool or the DTC Server.
If the Destination Type is set as SERVER, then the topology rule set for DTC pool cannot have only NOERR and NXDOMAIN rules. This is because the NAMED does not process the queries in the IDNS if the incoming requests are matched to LBDN with no topology balance method. Also, the pools under this LBDN do not have active or existing servers. Hence a NOERR response is always received. To prevent this behavior, the grid must have at least one active server as the Rule Destination under any DTC pool in the LBDN to allow IDS processing for the current LBDN and Pool. The rule set must have at least one rule with the REGULAR Return Type.
The Disable for DHCP checkbox must be not be selected to enable networks and to build the topology database. For more information about the checkbox, see Configuring IPv4 Networks.
The topology ruleset must have a specific order for the following rules:
REGULAR rules
NOERR rules
NXDOMAIN rules
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