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Question about RFC6724

Brian E Carpenter <brian.e.carpenter@gmail.com> Mon, 02 May 2022 04:32 UTC

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From: Brian E Carpenter <brian.e.carpenter@gmail.com>
To: 6man <ipv6@ietf.org>
Subject: Question about RFC6724
Message-ID: <985e9c94-b6f7-b45d-208d-e9b26664540b@gmail.com>
Date: Mon, 02 May 2022 16:32:46 +1200
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Hi,

Excuse my ignorance, but I have a question about RFC6724. The rules depend on longest prefix matching and therefore on the definition of CommonPrefixLen(S, D).

The way it's defined doesn't work for ::ffff:0:0/96, as far as I can see:

> 
> 2.2.  Common Prefix Length
> 
>    We define the common prefix length CommonPrefixLen(S, D) of a source
>    address S and a destination address D as the length of the longest
>    prefix (looking at the most significant, or leftmost, bits) that the
>    two addresses have in common, up to the length of S's prefix (i.e.,
>    the portion of the address not including the interface ID).  For
>    example, CommonPrefixLen(fe80::1, fe80::2) is 64.

The "interface ID" is simply a non-concept for IPv4-mapped IPv6 addresses. So what do implementations do? What is the common prefix length of ::ffff:10.1.0.10 and :ffff:10.1.0.1, in terms of the RFC6724 rules?

      Brian

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