[arin-ppml] ARIN-prop-127: Shared Transition Space for IPv4 Address Extension

Mark Andrews marka at isc.org
Mon Jan 24 19:15:49 EST 2011

In message <54E900DC635DAB4DB7A6D799B3C4CD8E066EBD at PLSWM12A.ad.sprint.com>, "Ge
orge, Wes E [NTK]" writes:
> > -----Original Message-----
> > From: Owen DeLong [mailto:owen at delong.com]
> > Sent: Monday, January 24, 2011 12:11 PM
> > To: George, Wes E [NTK]
> > Cc: Joel Jaeggli; arin-ppml at arin.net
> > Subject: Re: [arin-ppml] ARIN-prop-127: Shared Transition Space for
> > IPv4 Address Extension
> > 
> > > Read
> > >
> https://datatracker.ietf.org/doc/draft-ietf-intarea-shared-addressing-issues
> > > / for more discussion on the matter.
> > 
> > In which case, this address space only presents an issue for those
> > using
> > it in a manner other than intended.
> > 
> > Owen
> > 
> [WES] That's an oversimplification. This block will break 6to4 even if it's
> used for its intended purpose as long as the block is not part of RFC1918
> space, it just might break at a slightly different place in the path. A CPE
> router doing 6to4 for its network using the non-1918 IP it gets from the
> broadband provider will break just as much as an end host who gets a
> public-looking but non-unique/routable address. But whether ARIN/IANA
> reserves a block, the ISPs cooperate and use a block amongst themselves, or
> they use some of the space that was previously allocated to them by an RIR
> on an individual basis, the same problem exists. So it's not a surprise, but
> that's part of why I'm so adamant about using 1918 space for this if at all
> possible.
> Not to speak for Joel, but I think that the point he's making is that if
> this block isn't codified as an update/addition to RFC1918 space, it'll be
> treated incorrectly by applications which care about global uniqueness in
> addressing, regardless of where they live. Even if it is codified in that
> manner, it'll take the applications (host stack and otherwise) a while to
> catch up. 
> Wes George
Which is why ISP's should also provision 6rd relay routers and advertise
the appropriate DHCPv4 option if they do this.  6rd should be preferred
over 6to4 by any sane CPE.  6rd can be automatically enabled safely as
you shouldn't get the option returned if it is not supported/

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org

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