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Re: the shen-mpls-nnhop Was:(Re: thoughts on draft-bryant-shand-ipfrr-no

Subject: Re: the shen-mpls-nnhop Was:Re: thoughts on draft-bryant-shand-ipfrr-notvia-addresses-00.txt
From: Loa Andersson
Date: Wed, 18 May 2005 16:23:05 +0200
Alia,

we need to be careful so we talk about the same thing. The
shen-mpls-nnhop is intended for the mpls working group, has
been oreented there and asked to be made a working group
doc. That part belongs in mpls.

What you describe below is requirments on a solution. The
requirement work may very well be be done in rtgwg or anywhere
else.

Actual protocol design should be done by the working group
that owns the protocol.

/Loa

Alia Atlas wrote:

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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--
Loa Andersson

Principal Networking Architect
Acreo AB                           phone:  +46 8 632 77 14
Isafjordsgatan 22                  mobile: +46 739 81 21 64
Kista, Sweden                      email:  [email protected]
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