RE: [rfc2462bis issue 281] Requirement for 64bit I/F ID

[Pekka Savola <pekkas at netcore.fi>]

On Tue, 25 May 2004, Barany, Pete wrote:
> I also brought this issue up several months ago and received no
> follow-up. I agree that it is shortsighted.

For what it's worth, I think most ISPs use longer than 64 bit subnet
prefixes in numbering their loopback or point-to-point addresses, and
are quite happy about it.  

On the other hand, there are a number of features like SEND and 
RFC3041 which do use these features.  We don't want to get into the 
situation where people would start complaining that RFC3041/SEND would 
have to be forward-ported to arbitrary prefixlengths because folks 
later figured they'd prefer to use SEND/RFC3041 or something like that 
in the future.  In other words, I think using non-64 bit prefix 
lengths is just fine in the scenarios where you *know* that you won't 
be needing the possible fancy new features that could be provided only 
for 64 bit prefixes.

A comment below on your forwarded mail..

> More generally, I still don't see why there is a restriction on the
> prefix length for all IPv6 unicast addresses where the first 3 MSBs are
> other than 000. I could understand the wording in RFC 3513 (and RFC
> 3513bis) if the restriction was intended for "unicast addresses that are
> configured via stateless address autoconfiguration" (thus my initial
> comment about the need to update RFC 2462bis). But some operators may
> want to use DHCPv6 (stateful address autoconfiguration) where there is
> no concept of prefixes per se (just 128 bit addresses).  [...]

Actually, /64 makes some sense for DHCPv6 address assignment as well, 
because you want to aggregate the routing table entries at the first 
hop ISPs, assuming that you have multiple users on a subnet.

Of course, the length would not need to be exactly /64, but why not to
make it consistent for DHCPv6 and non-DHCPv6 alike..

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings


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