Subject: Re: [dnsext] FQDN maximum length

From: Mark Andrews <[email-masked]>
Date: Fri, 01 Jan 2010 10:10:04 +1100

Mark Andrews writes:
> 
> In message <[email-masked]>, Stuart Cheshire 
> wr
> ites:
> > On 30 Dec 2009, at 18:26, Mark Andrews wrote:
> > 
> > > What actually says is:
> > >
> > > labels		63 octets or less plus a length octet.
> > > names           255 octets or less terminating in the root label.
> > >
> > > which matches neither of your interpretions.
> > >
> > > Mark
> > 
> > 
> > Which page of which RFC are you quoting there?
> 
> RFC 1034
> 
> Internally, programs that manipulate domain names should represent them
> as sequences of labels, where each label is a length octet followed by
> an octet string.  Because all domain names end at the root, which has a
> null string for a label, these internal representations can use a length
> byte of zero to terminate a domain name.
> 
> To simplify implementations, the total number of octets that represent a
> domain name (i.e., the sum of all label octets and label lengths) is
> limited to 255.

Also RFC 1035.

3.1. Name space definitions

Domain names in messages are expressed in terms of a sequence of labels.
Each label is represented as a one octet length field followed by that
number of octets.  Since every domain name ends with the null label of
the root, a domain name is terminated by a length byte of zero.  The
high order two bits of every length octet must be zero, and the
remaining six bits of the length field limit the label to 63 octets or
less.

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.

> 
> > Stuart Cheshire <[email-masked]>
> > * Wizard Without Portfolio, Apple Inc.
> > * Internet Architecture Board
> * www.stuartcheshire.org
> > 
> > 
> -- 
> Mark Andrews, ISC
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: +61 2 9871 4742                 INTERNET: [email-masked]
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: [email-masked]