Subject: Re: [mpls] wg doc poll on draft-jin-mpls-mldp-leaf-discovery-04

From: Eric Rosen <[email-masked]>
Date: Mon, 06 Aug 2012 14:48:09 -0400

> this is to start a two week poll on adopting
> draft-jin-mpls-mldp-leaf-discovery-04 as an MPLS working group document.

No, do not support.

Applications that use BGP-based auto-discovery and/or signaling, e.g., MVPN,
already seem to have adequate mechanisms for discovering leaf nodes.  E.g.,
MVPN has the "Leaf Info Required" bit in PMSI Tunnel Attribute to indicate
when the tunnel root wants to know who all the leafs are, and the Leaf A-D
route  is used by the leafs to reply to the root.  A Leaf A-D route also
carries an RT to constrain distribution of the route to the root node.  The
draft defines a new AFI/SAFI, whose NLRI consists of an mLDP FEC element and
a leaf node address.  There is certainly no need for this in MVPN, as it
just duplicates existing functionality, in a less general way, and with no
comparable method of constraining distribution.

The MVPN BGP signaling allows a root node to determine which leaf nodes need
to receive which customer data streams.  In theory, this information could
be used to assign two different data streams to the same tunnel, if, e.g.,
the same set of leaf nodes need to receive both streams.  (Whether this is
actually useful in practice is arguable.)  However, the signaling proposed
in this draft only allows the root node to determine the leaf nodes who have
joined a particular mLDP LSP.  It doesn't convey any information about why a
particular leaf node has joined a particular LSP, so it's not really useful
if one is trying to decide whether two data streams should be sent on the
same tunnel.

I just don't see the use case for the draft's BGP mechanism.

I think the T-LDP mechanism is similarly problematic.  If an application is
not already using T-LDP for signaling, I don't think it makes much sense to
require that each leaf node initiate a new T-LDP session to each root node.
For security reasons, one usually doesn't accept T-LDP sessions from just
anyone; the set of possible T-LDP peers is either configured, or is
auto-discovered (via some BGP-based mechanism).  If BGP auto-discovery is
already being used, the T-LDP mechanism would not be needed, but if BGP
auto-discovery is not being used, we wouldn't want to require that each
potential root node be configured with the addresses of all the potential
leaf nodes.

We do have to remember that, in receiver-driven multicast, the fact that the
root node doesn't know all the leaf nodes is considered to be a scalability
advantage.

Also, I'm not at all sure what the root node would do with the information
that two P2MP LSPs have the same set of leaf nodes.  This fact by itself
does not mean that the two tunnels could be replaced by a single tunnel.
Even if it did, LDP has no mechanism for replacing one tunnel with another.
I don't think it's worthwhile setting up a whole bunch of new TCP
connections (and T-Hello adjacencies) just to convey a small amount of
not-very-useful information.

In summary:

- I don't really see what the use case is;

- Existing BGP A-D mechanisms for MVPN are better at providing the
  information an application really needs, and are better at constraining
  the distribution of the information;

- The T-LDP mechanism raises security issues and overhead issues, and
  it is not clear what to do with the information it conveys.

---

From: Thomas Nadeau <[email-masked]>
Date: Mon, 6 Aug 2012 15:19:16 -0400

+1

On Aug 6, 2012, at 2:48 PM, "Eric Rosen" <[email-masked]> wrote:

> _______________________________________________
> mpls mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/mpls

---

From: "Henderickx, Wim (Wim)" <[email-masked]>
Date: Mon, 6 Aug 2012 21:56:32 +0200

+1, I believe the additional complexities to link this mechanism to multiple applications is more complex than optimizing the P2MP/MP2MP LSP resources which might be shared with multiple applications.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Eric Rosen
Sent: maandag 6 augustus 2012 20:48
To: Loa Andersson
Cc: [email-masked]; [email-masked]
Subject: Re: [mpls] wg doc poll on draft-jin-mpls-mldp-leaf-discovery-04

No, do not support.

In summary:

---

From: "Dutta, Pranjal K (Pranjal)" <[email-masked]>
Date: Tue, 7 Aug 2012 01:33:00 +0530

+1. 

T-LDP is not the right choice for building an explicit relationship between root and leaf nodes. 

Scalability on mLdp comes from the fact that leaves and roots are decoupled in control plane, with no explicit dependency. 

Esp, since the draft describes VPLS-Mcast as problem context, there are solutions adopted in L2VPN/PWE3 to avoid full-mesh of T-LDP. 

Thanks,
Pranjal

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Eric Rosen
Sent: Monday, August 06, 2012 11:48 AM
To: Loa Andersson
Cc: [email-masked]; [email-masked]
Subject: Re: [mpls] wg doc poll on draft-jin-mpls-mldp-leaf-discovery-04

No, do not support.

In summary:

---

From: Chandrasekar R <[email-masked]>
Date: Thu, 16 Aug 2012 17:55:16 +0530

Do not support.

> From: [email-masked] [mailto:[email-masked]] On Behalf Of
> Loa Andersson
> Sent: Tuesday, July 31, 2012 5:41 PM
> To: [email-masked]; Martin Vigoureux
> Cc: [email-masked]
> Subject: [mpls] wg doc poll on draft-jin-mpls-mldp-leaf-discovery-04
> 
> Working group,
> 
> Please send your comments (support/not support) to the mpls working
> group mailing list ([email-masked]).
> 
> This poll ends August 17, 2012.
> 
> /Loa
> (mpls wg co-chair)
> --
> 
> 
> Loa Andersson                         email: [email-masked]
> Sr Strategy and Standards Manager            [email-masked]
> Ericsson Inc                          phone: +46 10 717 52 13
>                                               +46 767 72 92 13

---

From: "Eric Osborne (eosborne)" <[email-masked]>
Date: Thu, 16 Aug 2012 15:11:33 +0000

Sorry if this is late.

I saw that Kamran had some comments as part of the RT review.  The reply was that they would be addressed in the 'next version'.  I don't believe they have been, as -04 dates back to May 2012.  I don't believe WG status is warranted until the authors can make the changes they'd committed to.

eric

> Sent: Tuesday, July 31, 2012 8:11 AM

---

From: Thomas Morin <[email-masked]>
Date: Tue, 21 Aug 2012 14:10:49 +0200

Do not support.
As explained in a parallel post, I think the the gain/complexity balance 
is heavily tilted on the complexity side.

-Thomas

---

From: Ross Callon <[email-masked]>
Date: Tue, 21 Aug 2012 11:10:15 -0400

This poll has now ended. We do not have consensus to accept this document as a WG document. 

Ross
(for the WG chairs)

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Loa Andersson
Sent: Tuesday, July 31, 2012 8:11 AM
To: [email-masked]; Martin Vigoureux
Cc: [email-masked]
Subject: [mpls] wg doc poll on draft-jin-mpls-mldp-leaf-discovery-04

Working group,

this is to start a two week poll on adopting
draft-jin-mpls-mldp-leaf-discovery-04
as an MPLS working group document.

/Loa
(mpls wg co-chair)
--