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

On 14 Sep 2006, at 10:14, Robert Raszuk wrote:

> Francois,
>
>> This seems to be clearly defining associations between AFI/SAFI and
>> Next Hop. And it seems to be implying that only one type of Next Hop
>> can be associated with a AFI/SAFI pair.
>
> And I think this is fine
> as only one next hop can be present in MP_REACH
>  attribute today. How can you associate set to a single next hop :) ?
>

So, first, I think we now agree that rfc2858bis does talk about  
association between AFI/SAFI value and Next Hop Protocol.

The point is that if the Next Hop protocol is _identified_ by the AFI/ 
SAFI value, then, for a given NLRI format , you would need to  
systematically standardise two different AFI/SAFI pairs: one AFI/SAFI  
to advertise that NLRI format with an IPv4 Next Hop and another AFI/ 
SAFI pair to advertise that same NLRI with an IPv6 Next Hop (not in  
same MP_REACH of course, but possibly in different MP_REACH or simply  
in different networks). While this has been mentioned as potential  
approach, there has been arguments as to why this is not necessarily  
the best approach.

For example, the rt-constrain draft you co-authored currently defines  
a single AFI/SAFI pair (1/132) to advertise a Route Target membership  
NLRI, whether it is advertised with an IPv4 Next Hop or an IPv6 Next  
Hop. And then you use the Length to decide whether the Next Hop is  
IPv4 or IPv6. It seems to me that this somewhat contradicts the  
rfc2858bis statement saying that "the AFI/SAFI identifies the Next  
Hop protocol". It precisely does not, since it is instead identified  
by the Length.

Again, at this stage I am not trying close the debate as to which  
approach is best, I just want to make sure rfc2858bis is kept open to  
the candidate/existing approaches.

> Also note that the text you are proposing to edit is by itself not
> perfect already in the different angle. NH length is allowed to be  
> zero
> - and that is good - but once we make the length = 0 a lot of text in
> this rfc would need to be rewritten.
> Cheers,
> R.
>
>
>> Hi Robert,
>>
>> On 14 Sep 2006, at 09:54, Robert Raszuk wrote:
>>
>>> Francois,
>>>
>>> IMHO the AFI and SAFI paragraphs from rfc2858bis you are  
>>> proposing to
>>> edit talk about NLRIs to AFI/SAFI associations and not indicate
>>> characteristics of the next hop itself.
>>>
>>
>> The text says:
>>
>> "
>> Address Family Identifier (AFI):
>>
>>          This field in combination with the Subsequent Address Family
>>          Identifier field identifies the Network Layer protocol
>>          associated with the Network Address of Next Hop and the
>>          semantics of the Network Layer Reachability Information that
>>          follows.
>> "
>>
>> so in particular AFI/SAFI "identifies the network layer protocol
>> associated with the network address of Next Hop".
>>
>> This seems to be clearly defining associations between AFI/SAFI  
>> and Next
>> Hop. And it seems to be implying that only one type of Next Hop  
>> can be
>> asociated with a AFI/SAFI pair.
>> What am I missing?
>>
>> Francois
>>
>>
>>> Cheers,
>>> R.
>>>
>>>
>>>
>>>
>>>
>>
>

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