On 13 Feb 2012, at 22:01, Dave Thaler wrote:
> 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.
> [...]
I certainly agree that that wording can be improved.
Tim
>
>> 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.
>
> 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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