2009-03-18 - News - Chris Thompson
We have started to use a scheme involving DNAMEs (domain aliases) for the reverse lookup up of some IP addresses within the CUDN. The primary motivation is to reduce the number of individual reverse zones. A description of the mechanism, written for an audience not restricted to the university, can be found in
http://people.pwf.cam.ac.uk/cet1/prune-reverse-zones
- Moved to https://www.dns.cam.ac.uk/domains/reverse/
At the moment we are using this method for these address ranges:
- 192.153.213.*
192.84.5.*
- these subnets are or will be used for CUDN infrastructure (although within the CUDN, the corresponding reverse zones are not listed in the sample.named.conf configuration)
128.232.[128-223].*
- some of this address space will be used for Eduroam
Some nameserver software (especially Windows DNS Server) may be unable to cope with zones containing DNAMEs: they will have to avoid stealth slaving (for example) 232.128.in-addr.arpa. We don't believe that any stub resolvers fail to cope with the "synthesised CNAMEs" generated from DNAMEs, although at least some versions of the glibc resolver log warning messages about the DNAME (but give the right answer anyway). If anyone experiences problems as a result of what we are doing, please let us know.
In the light of experience, we may later extend this scheme to other address ranges, e.g. 128.232.[224-255].* which is currently covered by 32 separate reverse zones. However, we will give plenty of warning before making such a change.