what's a valid domain name?

[Mark Andrews]

In message <20110129053051.BAD452D11F at mail.nsbeta.info>, pyh at mail.nsbeta.info w
rites:
> Barry Margolin writes: 
> 
> > In article <mailman.1559.1296265826.555.bind-users at lists.isc.org>,
> >  pyh at mail.nsbeta.info wrote: 
> > 
> >> I  googled and found this: 
> > 
> > It's on the Internet, so it must be true. :) 
> > 
> >> 
> >>     * A domain name can be up to 63 characters long plus a dot plus the 
> >> characters used to identify the top-level domain (i.e "com", "info", "biz"
> , 
> >> etc.
> >>     * Valid characters in a domain name include letters, numbers and 
> >> hyphens "-". The domain name must start and end with a letter or number.  
> >> 
> >> 
> >> So, for this domain name of   
> >> "www.xyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxyxy.com"
>  
> >> whose size is larger than 64, is not a valid domain name?  
> >> 
> >> And is there a RFC item for a valid domain name? 
> > 
> > RFC 1035 section 3.1 says: "To simplify implementations, the total 
> > length of a domain name (i.e., label octets and label length octets) is 
> > restricted to 255 octets or less." 
> > 
> > The length of each label within a domain name is limited to 63 
> > characters. 
> > 
> 
> Thanks for the kind info. 

Remember domain names are not the same things as hostnames.  Hostnames
are limited to letter digit hyphen (LDH).  Other domain names are not
limited and things last SRV records deliberately use labels that are
not legal in hostnames to prevent collisions of the two namespaces when
they are stored in the DNS.


> Regards.
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org