On Dec 21, 2012, at 8:45 AM, Marek Kozlowski wrote: > As I can see BIND allows duplicate A: > > pikus IN A 192.168.1.1 > pikus IN A 192.168.1.2
Those aren't duplicates. They are a record set of two records. If they had the same data, we would call them duplicates. A record set is a set of records that all have the same name, class, and type. Also called an rrset, short for "resource record set". > and PTR: > > 192.168.1.1. IN PTR pikus.somedomain.com. > 192.168.1.1. IN PTR filemon.somedomain.com. Again, an rrset of PTR records. > and disallows duplicate CNAMEs in the same way. CNAME is a singleton type. Each rrset of type CNAME must have exactly one record, no more. Furthermore, a CNAME record cannot coexist with any other record type of the same name, except for a couple of DNSSEC record types (RRSIG and NSEC). > For A and PTR both > records are returned. My questions are: > > 1. Is using duplicate A and PTR a standard (RFC...?) supported by all > named implementations? Yes. > 2. Is using this duplicate A / PTR a good practice? That depends on the use case. Multiple PTR records in an rrset is typically a bad idea (won't achieve the desired effect), but that is not always the case. Putting multiple A records in an rrset is common. > 3. If A can be duplicated and CNAME cannot -- what's the reason for > using CNAMEs (A-s are better). A CNAME record creates an alias. If the target of that alias changes (gets a new address, gets a new MX record, or whatever), the alias need not change to gain the same benefit. Deciding when to use a CNAME record in place of one or more other records is a matter of taste, management tools, and use cases. Chris Buxton BlueCat Networks _______________________________________________ Please visit https://lists.isc.org/mailman/listinfo/bind-users to unsubscribe from this list bind-users mailing list bind-users@lists.isc.org https://lists.isc.org/mailman/listinfo/bind-users
