Re: the shen-mpls-nnhop Was:(Re: thoughts on draft-bryant-shand-ipfrr-notvia-addresses-00.txt)

[Alia Atlas <[e-mail]>]

Loa,

In this case, I agree with Stewart. (Much less usual than Stewart agreeing 
with Mike :-)

To my mind, the IP FRR work that has been going on in rtgwg also applies to 
LDP.  LDP, after all, learns its next-hops from the IGP.  I have been 
referring to this work as IP/LDP FRR since the beginning and certainly 
advocating for its applicability to LDP as well.

There are two points that I can see where there could be additional work 
for the mpls wg.   First, LDP FRR requires knowledge of labels from 
neighbors who are not the primary neighbors.  This means that the 
loop-checking which can be enabled in LDP should not be (at least for the 
non-primary neighbors)- because the label bindings do not all represent 
paths that would be taken.  This  doesn't require changes to LDP; it is a 
detail of the required mode.  There could be more text in the LFA draft to 
reflect the acceptable LDP modes/configurations that would work.

Second, an advanced method may require extensions to support label 
discovery.  For U-turn alternates, the requirement is merely that a router 
advertise its label bindings to all neighbors - not merely those that are 
primary.  This is already clearly within the LDP spec - and a good idea for 
convergence reasons.  Thus, there's no work required for that aspect.  For 
U-turn alternates, for the explicitly marked U-turn packet, I do use a 
specific label that all implementations need to use in common; ideally 
that'd be a reserved label (13) but I haven't tried to start that 
discussion, until the future of U-turn alternates becomes more clearly 
defined.  For a tunnel approach that has the tunnel egressing at the 
next-next-hop, Naiming's idea of learning label bindings via a neighbor 
might be helpful.  For the tunnel approaches, there's also the 
potential/probable need for targeted sessions to support multi-homed 
prefixes, but that requires no extensions.  For a tunnel approach, it is 
highly likely that one tunnel technology used would be LDP, since that uses 
a hardware mechanism clearly supported today.

My expectation was that the rtgwg would need to last-call the IP/LDP FRR 
work in the MPLS WG, as well as the ISIS and OSPF WGs, because of the 
applicability there.

What do you think?

Alia

At 09:26 AM 5/18/2005, Stewart Bryant wrote:


>Loa Andersson wrote:
>>Maiming and Stewart,
>>you wrote - and I guess this is valid:
>>Naiming Shen wrote:
>>
>>>I think the needs start emerging, any important services
>>>riding on top of IP/MPLS transport infrastructure needs
>>>fast convergence services. It's not reasonable to assume
>>>only RSVP-TE LSPs need fast reroute, and other
>>>network transport does not. This nnhop-ldp draft is to
>>>facilitate the LDP based MPLS network for FRR with
>>>node protection. I have been talking to some providers
>>>in the past year, there are certainly interests in
>>>this service.
>>
>>Stewart Bryant wrote:
>>  >
>>  > I think the interest that we are seeing in IPFRR for LDP
>>  > networks demonstrates the usefulness of this work. Sure
>>  > RSVP-TE FRR exists, but some customers have expressed
>>  > an interest in a solution that does not use RSVP.
>>  >
>>However the MPLS working group need to take a decision if,
>>when and how this futopicctionality should be developed.
>>
>>The way of doing this would be
>>- write down the requirements
>>- send them to the mpls wg
>>- we go through the moces to establish the mpls wg consensus
>>Comments:
>>- I don't think FRR for LDP based MPLS enabled IP networks
>>   should not go into the rtgwg, the charter of the rtgwg seems
>>   to say the rtgwg takes of everything that does not fit into
>>   other routing are working groups (Alex and Bill comments on this?)
>
>I disagree.
>
>Whilst the MPLS WG must be engaged in this work, to do it
>exclusively in MPLS WG would be a mistake.
>
>The work that we have done to date has achieved a high degree
>of commonality between the IP solution and the MPLS solution.
>Maintenance of that commonality would be at risk if the
>MPLS WG struck out in their own direction. This work
>requires a significant knowledge of the working of routing
>protocols and therefore RTGWG (or perhaps a new WG in routing)
>would seem a more natural home than MPLSWG.
>
>>- my take is that for this purpose you could either document
>>   the requirements in a separate document or put them into one
>>   the existing documents. I've no preferences, but this should
>>   be rather short.
>
>I think that we need an FRR requirements draft.
>
>BTW the scope is further widened by the applicability of elements
>of the solution (loop free convergence) to network management.
>
>>- my preference would be to speed this up so we could have
>>   a decision going into the Paris meeting.
>>Also I think it will be right to take this discussion to the
>>mpls wg list. I will write a mail to mpls list to that effect.
>
>Certainly the MPLS WG need to be an aware and active participant
>in this work, but please do not precipitate a schism.
>
>- Stewart
>
>>/Loa
>
>
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