4.2. Recursive Resolvers

Whether the recursive resolver is aware of SVCB or not, the normal response construction process used for unknown RR types [RFC3597] generates the Answer section of the response. Recursive resolvers that are aware of SVCB SHOULD help the client to execute the procedure in Section 3 with minimum overall latency by incorporating additional useful information into the Additional section of the response as follows:

1. Incorporate the results of SVCB resolution. If the recursive resolver's local chain length limit (which may be different from the client's limit) has been reached, terminate.

2. If any of the resolved SVCB records are in AliasMode, choose one of them at random, and resolve SVCB, A, and AAAA records for its TargetName.

   • If any SVCB records are resolved, go to Step 1.

   • Otherwise, incorporate the results of A and AAAA resolution, and terminate.

3. All the resolved SVCB records are in ServiceMode. Resolve A and AAAA queries for each TargetName (or for the owner name if TargetName is "."), incorporate all the results, and terminate.

In this procedure, "resolve" means the resolver's ordinary recursive resolution procedure, as if processing a query for that RRset. This includes following any aliases that the resolver would ordinarily follow (e.g., CNAME, DNAME [DNAME]). Errors or anomalies in obtaining additional records MAY cause this process to terminate but MUST NOT themselves cause the resolver to send a failure response.

See Section 2.4.2 for additional safeguards for recursive resolvers to implement to mitigate loops.

See Section 5.2 for possible optimizations of this procedure.