Dave, another point below.
On 2012/02/14, at 8:55, Dave Thaler wrote: >> -----Original Message----- >> From: Dave Thaler >> Sent: Monday, February 13, 2012 2:01 PM >> To: Dave Thaler; 'Chris Grundemann'; 'Brian E Carpenter' >> Cc: 'ipv6@ietf.org'; '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. >> 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. AFAIK, neither RFC 3484 nor -revise specifies source address selection algorithm for an IPv4 destination address. Simply, it is out of scope of these documents. Do you want to cover these issues in the revision ? Best regards, > > -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 > > -------------------------------------------------------------------- > IETF IPv6 working group mailing list > ipv6@ietf.org > Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 > -------------------------------------------------------------------- -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------