cname rr data lookup
kcd at daimlerchrysler.com
Fri Jan 3 22:28:18 UTC 2003
Graham Turner wrote:
>as a migration step of hosts say olddomain.com to newdomain.com I am
>planning to provide a whole load of alias CNAME records in the zone file for
>newdomain.com along the lines of
>host1.newdomain.com IN CNAME host2.olddomain.com
>this is to support the correct name resolution of a legacy host in
>olddomain.com 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 newdomain.com
>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 olddomain.com
>2. do i have to make the dns server that is hosting newdomain.com
>authoritative for the olddomain.com by making it a secondary to the legacy
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).
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