I support the idea of qname minimization, but I think there is a common case where it will cause additional DNS round trips, slowing the response and increasing the number of packets and queries the servers must handle.
Consider “www.host.group.department.example.com” where the company’s servers are authoritative for the zones: example.com department.example.com group.department.example.com Without minimization (typical today): 1. Query root for “www.host.group.department.example.com”, get list of “com” servers. 2. Query a com server for “www.host.group.department.example.com”, get list of “example.com” servers. 3. Query an example.com server for “www.host.group.department.example.com”, get answer. With minimization: 1. Query root for “com”, get list of “com” servers. 2. Query a com server for “example.com”, get list of “example.com” servers. 3. Query an example.com server for “department.example.com”, get list of “ department.example.com” servers (which happens to be the same as the list of “example.com” servers). 4. Query a “department.example.com” server (likely the same server as step 3) for “group.department.example.com”, get list of “ group.department.example.com” servers. 5. Query a “group.department.example.com” server for “host.group.example.com”, get probably just an A and/or AAAA record, indicating there is no zone cut at that level. 6. Query a “group.department.example.com” server for “ www.host.group.department.example.com”, get answer. Note that it takes twice as many queries, and each depends on the previous, so it is twice as many round trips. I realize that caching will reduce the extra queries in many cases, but can we estimate the impact of this somehow, to determine if it is significant? -- Bob Harold DNS hostmaster, University of Michigan
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