cname rr data lookup

Kevin Darcy kcd at
Fri Jan 3 22:28:18 UTC 2003

Graham Turner wrote:

>as a migration step of hosts say to I am
>planning to provide a whole load of alias CNAME records in the zone file for
> along the lines of
>this is to support the correct name resolution of a legacy host in
> in a transition phase from client whose resolver configuration
>(and by implication its default devolution of unqualified names which is
>less preferable to modify) reflects
>for this to work the name in the data section of the CNAME RR must be
>resolvable using a host record.
"Host record"? I assume you mean an A record.

>assuming this is a valid configuration what (if any) rules are there on the
>name server being able to resolve this host record from say either;
>1. domain delegated to the legacy dns server(s)  hosting
>2. do i have to make the dns server that is hosting
>authoritative for the by making it a secondary to the legacy
>dns server
No, you're not forced to make either server slave anything from the 
other server. However, there are some important rules about CNAMEs that 
you need to be aware of:

1) You can't point an MX record or an NS record at a CNAME. So your 
delegation and MX targets (Internet SMTP mail server names) must still 
be A records.
2) If a name owns a CNAME record, it cannot own any other records. The 
most common gotcha associated with this rule is that the name of a zone 
cannot own a CNAME (because then the SOA and NS records owned by the 
name would violate the rule).

                                        - Kevin

More information about the bind-users mailing list