When a DNS name is configured for a group in an SSM map, a DNS request is sent to resolve the name. If static sources are already configured for the group, it takes precedence and the DNS request is not sent. This feature uses the AAAA record type. For example, if the multicast group is FF30::1234:5678 and the configured domain name is ext.foo.bar, then the DNS request is sent for 184.108.40.206.220.127.116.11.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.3.F.F.ext.xxx.xxx.
The DNS request is not sent every time a report is received. A DNS request is sent only in the following scenarios:
The DNS response may contain one or more addresses. These addresses are updated to the SSM mapping table against the specific group.
NoteLPM is used to match the group for a DNS response.
If a static source is configured for a group for which DNS resolved addresses are already present, the dynamic sources are flushed and the static sources are added. Static mapped addresses are preferred over DNS resolved addresses.