Can the value for a NS record be an IP address?

Until today I was used to believe it couldn't. From this page

The name field can be any of:

1. A Fully Qualified Domain Name (FQDN) e.g. example.com. (ends with a dot)
2. An unqualfied name (does not end with a dot)
3. An '@' (substitutes the current value of $ORIGIN)
4. a 'space' or 'blank' (tab) - this is replaced with the previous value of the name field.

Now, look at the following query

$ dig top-immotunisie.com NS

; <<>> DiG 9.6.0-APPLE-P2 <<>> top-immotunisie.com NS
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44156
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;top-immotunisie.com.       IN  NS

;; ANSWER SECTION:
top-immotunisie.com.    36012   IN  NS  ns1.topnet.tn.
top-immotunisie.com.    36012   IN  NS  196.203.251.8.

;; Query time: 353 msec
;; SERVER: 85.37.17.16#53(85.37.17.16)
;; WHEN: Thu Jan  7 02:29:15 2010
;; MSG SIZE  rcvd: 91

How is it possible? Can a NS record point to an IP address?

Solution 1:

That's not an IP address, it's a very, very invalid FQDN. In other words, it's a string of characters rather than an actual address. The dot at the end of the IP address gives it away, along with the specs in the RFC that state that an NS record answer is a string.

Interestingly, I just checked the domain you gave and it's already been fixed up to use ns2.topnet.tn as it's other nameserver.