RE: [Epp-rtk-devel] contact field lengths (fwd)

[Edward Lewis <lewis@tislabs.com>]

At 5:29 PM -0500 11/15/01, budi@alliance.globalnetlink.com wrote:
>I still remember that long time ago domain name cannot
>start with number. (Forgot the RFC number.)
>ie. you cannot register 2good2betrue.com

That's not true.  There is a common misconception about this.  The
restriction you are referring to is for "host names" not "domain names."
E.g., 3com.com is legal.

RFC 1035 states the rules about domain names, 1123 about host names.

>My point is, let's make it as flexible as possible.
>I vote for 255, not 64.

Here is the text from RFC1035 defining domain names:

# 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.
#
# Although labels can contain any 8 bit values in octets that make up a
# label, it is strongly recommended that labels follow the preferred
# syntax described elsewhere in this memo, which is compatible with
# existing host naming conventions.  Name servers and resolvers must
# compare labels in a case-insensitive manner (i.e., A=a), assuming ASCII
# with zero parity.  Non-alphabetic codes must match exactly.

What this says is that labels are limited to 63 octets, and that the whole
name is limited to 255 bytes (to simplify implementations).  I.e., a name
server's host name may be roughly 255 bytes long.  Note that 255 is the
binary length.  If the convention of \DDD is used (mentioned in 1035), the
real full length may be about 1K bytes.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=--=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Edward Lewis                                                NAI Labs
Phone: +1 443-259-2352                      Email: lewis@tislabs.com

Opinions expressed are property of my evil twin, not my employer.