[Softwires] Re: [Idr] Re: Last Call: 'Connecting IPv6 Islands over IPv4 MPLS using IPv6 Provider Edge Routers (6PE)' to Proposed Standard

David,

> Yakov, Bill -
> 
> Having read the document I have some initial comments. First, 6PE is an
> excellent solution. Overstating the obvious (perhaps my greatest talent),
> this is a solution for the subset of softwire problems that would be used
> for 6-over-4 when the encaps policy is "always use MPLS" and there are no
> security requirements. I will leave the question of 'no security
> requirements' for this solution to others.
> 
> The major deficiency from a softwires vantage point is that the v4 NH  gets
> encoded in a  v6 format, but semantically it's  v4 and this encoding trick
> doesn't work when you're doing v6 over v4. This is not to say the solution
> doesn't work but, since softwires has to solve both v4 over v6 and v6 over
> v4 (and variants including VPNs); I strongly urge that we don't have
> multiple techniques to derive the AF of the NH.

As we move forward, I agree with the goal of having a single technique 
to derive AF of the NH within the context of MP_REACH/MP_UNREACH.

> The current advancement of multiple techniques that require either encoding
> or length-check should be cleared up and made obvious and consistent. 
>
> I recommend some number of bits (or a byte) be used to state clearly what the
> AF of the NH is and leave in original encoding. A capability can be added to
> make sure that a peer can understand the new bits. Of course, I am looking
> for the minimal change to the doc and to BGP but, this matter needs to be
> discussed. The assumptions becoming embedded in the techniques of how to
> figure out what the actual AF of the NH could be easily cleared up w/ the
> suggestion of just very small number of bits and a capability in BGP.

While having "new bits" may be sufficient, it is by no means
necessary. This is because the current/original encoding already
provides a way to distinguish between IPv4 and IPv6 addresses in
the NH of MP_REACH/MP_UNREACH. I am referring to the approach
already used in several documents approved by the IETF (e.g.,
draft-ietf-l2vpn-signaling, draft-ietf-l3vpn-rt-constrain,
draft-ietf-l2vpn-vpls-bgp) where the NH Length field is used
to distinguish between IPv4 and IPv6 as the NH.

And just for completeness, the current/original encoding provides
yet another way to distingush between IPv4 and IPv6 as the NH
addresses - use two different SAFIs to distinguish between IPv4 and
IPv6 as the NH. However, I am not aware of any IETF technologies
that use this approach.

Yakov.

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