about the MX and NS values

Matus UHLAR - fantomas uhlar at fantomas.sk
Thu Feb 9 07:42:43 UTC 2012

On 09.02.12 15:13, Jeff Peng wrote:
>I was thinking why RFC requires the values of MX and NS must be 
>hostname not IP.

because it IS the hostname, not an IP.

A points to IP(v4)
AAAA points to IP(v6)
NS, MX, PTR, CNAME... all others point to hostname.

otherwise, someone would need to decide what is an IP and what is not.

for example, can be an IP, but also a domain name of The only way you can decide which one it is, it 
the RR type.

those "common mistaked" of putting IP address into NS or MX reault 
either into

<domain> IN MX<domain>.
<domain> IN NS<domain>.

or into 

<domain> IN MX
<domain> IN NS

where 4. is not a valid TLD and thus they point nowhere.

>Any glue? Thanks.

you probably mean a clue ;-)
Matus UHLAR - fantomas, uhlar at fantomas.sk ; http://www.fantomas.sk/
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