Re: [Int-area] Revving draft-intarea-shared-addressing-issues

["George, Wes E IV [NTK]" <[e-mail]>]

-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf Of Dan Wing
Sent: Monday, June 14, 2010 4:16 PM
To: 'Bernard Aboba'; [e-mail]; [e-mail]
Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]
Subject: Re: [Int-area] Revving draft-intarea-shared-addressing-issues



> -----Original Message-----
> From: Bernard Aboba [mailto:[e-mail]]
> Sent: Monday, June 14, 2010 1:05 PM
> To: [e-mail]; [e-mail]; [e-mail]
> Cc: [e-mail]; [e-mail];
> [e-mail]; [e-mail]
> Subject: RE: [Int-area] Revving draft-intarea-shared-addressing-issues
>
> The NAT box can use its public IPv4 address to enable 6to4,
> thereby providing IPv6 support for hosts "behind" it.  Why
> would this result in a disconnected IPv6 island?

Diagram of what I understand the problem to be with 6to4
behind another NAT:

  IPv6 host--+
              \
               +---[home NAT]----[Carrier's NAT]---[Internet]
              /      ^       ^                  ^
  IPv6 host--+       ^       ^                  ^
                     ^       ^             IP address sharing
                     ^       ^             with multiple
                     ^       ^             subscribers
                     ^       ^
                     ^     the in-home NAT's WAN address
                     ^     is not publicly routable
                     ^
                     ^
               this in-home
             NAT turns on 6to4

Two comments -
This should only be a concern if the carrier NAT is allocating non-RFC1918 IPs to end users in the place of 1918 space, thus confusing the home router/host into thinking that it can make 6to4 work properly. Non-broken 6to4 implementations recognize 1918 space and don't try to use it as a 6to4 source. They don't recognize 11.0/8 as unroutable because it's being "borrowed" for use inside a NAT when 10.0/8 is exhausted.

This specific issue is definitely something we should capture as an issue with shared addresses. It might be fixable by having a local 6to4 relay to translate the traffic to native IPv6 before it leaves the NAT domain, but you'd need a NAT66 to handle the fact that the 6to4 address is only locally significant. And that's ugly, but since it's probably not possible to simply say "don't use 6to4" unless you are going to track down and replace all 6to4 end devices with those that speak native IPv6, you may not have a choice.

Wes George

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