Re: address vs. prefix (was: RFC7084)

Alexandru Petrescu <alexandru.petrescu@gmail.com> Wed, 11 December 2013 15:53 UTC

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Date: Wed, 11 Dec 2013 16:53:33 +0100
From: Alexandru Petrescu <alexandru.petrescu@gmail.com>
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To: "STARK, BARBARA H" <bs7652@att.com>, Wuyts Carl <Carl.Wuyts@technicolor.com>, "<ipv6@ietf.org>" <ipv6@ietf.org>
Subject: Re: address vs. prefix (was: RFC7084)
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Le 11/12/2013 16:02, STARK, BARBARA H a écrit :
>
>> But WPD-4 is not ok, for the simple reason that O=1 means
>> stateless.
>
> Per RFC4861 "When set, it [the O flag] indicates that other
> configuration information is available via DHCPv6." The word
> "stateless" is not present. As has been discussed, the word
> "addresses" in the M-flag definition is interpreted differently by
> different people, and some think it includes prefixes and some
> don't.

I agree some times people mix address and prefix in common talk.

There is a multiple distinction to be made.

First, yes, an address configured on an interface must have a prefix
length (as in IPv4 it must have a subnet mask).  By language abuse, or
simple convenience, some say an address and prefix are configured by
SLAAC, when actually just an address is configured by SLAAC.  (the plen
of the configured address is actually obtained by a substraction
operation from a predefined length of Interface ID; the plen offered in
RA is not for forming an address, but for on-link determination of ND).

Second, there is a difference between the prefix advertised by RA, and a
delegated prefix.  The difference is the following:

The prefix advertised by RA is to be used on that link, or on other
links on the side of the router originating the RA; whereas the prefix
delivered by a Prefix Delegation operation must not be used on that
link, and should be used on other links on the side of the router
requesting this prefix.

(this second difference is so much missed by specifiers at 3GPP.)

Alex