Home / server / Questions / 222641
Accepted
Mark Wagner
Asked: 2011-01-15 11:36:54 +0800 CST

In DNS can an IN NS point to a CNAME?

  • 772

Is it allowed to have an NS record be a CNAME? E.g.:

subdomain.example.com.       IN NS  ns1.example.com.
ns1.example.com.             CNAME  foo.example.com.
foo.example.com.             IN A   10.1.1.1

This doesn't seem to work in bind though this (of course) does:

subdomain.example.com.       IN NS  foo.example.com.
foo.example.com.             IN A   10.1.1.1

Any pointers to RFCs prohibiting this setup would be appreciated.

domain-name-system cname-record ns-record

1 Answers

  1. Best Answer

    RFC 1035 defines the NS resource record (RR) merely as a domain-name without specifying the RR type of the target (though it does make it clear that it can't be an IP).

    RFC 1912 has more specifics, in section 2.4:

    Having NS records pointing to a CNAME is bad and may conflict badly with current BIND servers. In fact, current BIND implementations will ignore such records, possibly leading to a lame delegation. There is a certain amount of security checking done in BIND to prevent spoofing DNS NS records. Also, older BIND servers reportedly will get caught in an infinite query loop trying to figure out the address for the aliased nameserver, causing a continuous stream of DNS requests to be sent.

    As was later pointed out in the comments, RFC 2181 Section 10.3 has a clear prohibition against this:

    MX and NS records

    The domain name used as the value of a NS resource record, or part of the value of a MX resource record must not be an alias. Not only is the specification clear on this point, but using an alias in either of these positions neither works as well as might be hoped, nor well fulfills the ambition that may have led to this approach. This domain name must have as its value one or more address records. Currently those will be A records, however in the future other record types giving addressing information may be acceptable. It can also have other RRs, but never a CNAME RR.

    • 25