> -----Original Message-----
> From: Dave Thaler
> Sent: Monday, February 13, 2012 2:01 PM
> To: Dave Thaler; 'Chris Grundemann'; 'Brian E Carpenter'
> Cc: '[email protected]'; 'Brian Haberman'; 'Bob Hinden'
> Subject: RE: 6MAN WG Last Call: draft-ietf-6man-rfc3484-revise-05.txt
>
> Yet another problem in draft-ietf-6man-rfc3484-revise...
>
> Section 2.4 (Private IPv4 address scope):
> [...]
> > The algorithm currently specified in RFC 3484 is based on the
> > assumption that a source address with a small scope cannot reach a
> > destination address with a larger scope.
> [...]
>
> The above sentence is simply not true, it was NOT based on such an assumption
> at all. It was based on the assumption that it was
> less likely to work. There's two reasons why it's less likely to work.
> First, it might or might not be able to reach it (the text overstates by
> saying it
> cannot... it was acknowledged that it may or may not).
> Second, if it goes through a NAT, it might not work for protocols that embed
> IP
> addresses in payloads.
> [...]
>
> > Due to this assumption, in the presence of both a NATed private IPv4
> > address and a transitional address (like 6to4 or Teredo), the host
> > will choose the transitional IPv6 address to access dual-stack peers
> > [I-D.denis-v6ops-nat-addrsel]. Choosing transitional IPv6
> > connectivity over native IPv4 connectivity, particularly where the
> > transitional connectivity is unmanaged, is not considered to be
> > generally desirable.
> >
> > This issue can be fixed by changing the address scope of private IPv4
> > addresses to global.
>
> Section 10 of RFC 3484 contained many examples. -revise contains
> no such example of what it's talking about, so I have to guess. Let's look
> at 3
> cases.
>
> Case 1:
> D set = { global IPv6, global IPv4 }
> S set = { Teredo IPv6, RFC1918 IPv4 }
>
> Under RFC 3484 rules, Destination Address Selection would prefer the Teredo
> connectivity under rule 2 (Prefer matching scope).
>
> Under -revise rules, Destination Address Selection would still prefer the
> Teredo
> connectivity under rule 6 (Prefer higher precedence), since the precedence of
> the (non-Teredo) destination address
> beats the precedence of the IPv4 address. Hence -revise
> does not change the behavior in this case.
Dmitry Anipko pointed out that rule 5 (Prefer matching label) would cause
the -revise rules to prefer IPv4. Still, I'd prefer a solution that doesn't
solve
this problem by creating another one (case 3). That is, we should fix a
problem
rather than just move it around.
I'll think about this and see if I can come back with a proposal.
-Dave
>
> Case 2:
> D set = { Teredo IPv6, global IPv4 }
>
> Not an interesting case because Teredo addressing should be disabled when a
> host has a global IPv4 address.
>
> Case 3:
> D set = { global IPv4 = 1.2.3.4 }
> S set = { NAT-ed IPv4 = 10.2.3.4, global IPv4 = 128.66.3.4 }
>
> Under RFC 3484 rules, Source Address Selection would prefer the global IPv4
> address under Rule 2(Prefer appropriate scope).
> Under -revise rules, Source Address Selection would instead prefer the NAT'ed
> IPv4 under Rule 8 (Longest matching prefix).
>
> This is broken. I don't see a real case the proposed change
> fixes, I only see real cases it breaks.
>
> -Dave
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