5. DNS server configuration

In the short term, whilst directory service technology and further types of DNS resource record are being developed, domain name administrators are encouraged to use these common names for the network services they run. They will make it easier for outsiders to find information about your organization, and also make it easier for you to move services from one machine to another.

There are two conventional approaches to creating these DNS entries. One is to add a single CNAME record to your DNS server's configuration, e.g.

        ph.hivnet.fr. IN CNAME baby.hivnet.fr.

Note that in this scenario no information about ph.hivnet.fr should exist in the DNS other than the CNAME record. For example, ph.hivnet.fr could not contain a MX record.

An alternative approach would be to create an A record for each of the IP addresses associated with ph.hivnet.fr, e.g.

        ph.hivnet.fr. IN A 194.167.157.2

It isn't a simple matter of recommending CNAMEs over A records. Each site has it's own set of requirements that may make one approach better than the other. RFC 1912 [RFC-1912] discusses some of the configuration issues involved in using CNAMEs.

Recent DNS server implementations provide a "round-robin" feature which causes the host's IP addresses to be returned in a different order each time the address is looked up.

Network clients are starting to appear which, when they encounter a host with multiple addresses, use heuristics to determine the address to contact - e.g. picking the one which has the shortest round-trip- time. Thus, if a server is mirrored (replicated) at a number of locations, it may be desirable to list the IP addresses of the mirror servers as A records of the primary server. This is only likely to be appropriate if the mirror servers are exact copies of the original server.