Subject: [mpls] Section 2.3 of of draft-ietf-mpls-mldp-in-band-signaling-01

From: Yakov Rekhter <[email-masked]>
Date: Tue, 16 Mar 2010 13:31:34 -0700

Folks,

>From 2.3:

   In order transport the packets of sender only branch to the root of
   the LSP a MP2MP is created.  This will cause the sender only branches
   to receive each others packets.  These packets will be dropped and
   not forwarded, if that affect is undesireable some other means of
   transport has to be established to forward packets to the root of the
   tree, like a Multi-Point to Point LSP for example.  A technique to
   unicast packets to the root of a P2MP or MP2MP LSP is documented in
   [I-D.rosen-l3vpn-mvpn-mspmsi] section 3.2.2.1 and
   [I-D.ietf-mpls-ldp-p2mp] section 3.

Section 3.2.2.1 of [I-D.rosen-l3vpn-mvpn-mspmsi] uses wildcard MVPN
S-PMSI auto-discovery routes, augmented with a new BGP attribute
"PPMP Label".

It is quite clear that if one wants to use MVPN S-PMSI auto-discovery
routes, then for the purpose of this draft wildcard MVPN S-PMSI
auto-discovery routes are sufficient - one does not need the PPMP
Label attribute. All you need to do is to set the Tunnel Type of
the PMSI Tunnel attribute of these routes to Ingress Replication.

However, one could also observe that in order to unicast packets
to the root of the MP2MP LSP the procedures specified in section 3
of of [I-D.ietf-mpls-ldp-p2mp] are sufficient. Quoting from that
section:

   One way to build a Shared Tree is to build an LDP P2MP LSP rooted at
   a common point, the Shared Root (SR), and whose leaves are all the
   members of the group.  Each member of the Shared Tree unicasts
   traffic to the SR (using, for example, the MP2P LSP created by the
   unicast LDP FEC advertised by the SR); the SR then splices this
   traffic into the LDP P2MP LSP.

In other words, in order to unicast packets to the root of the MP2MP
LSP all you need to do is for the root to advertise in LDP its
unicast FEC - you don't need MVPN S-PMSI auto-discovery routes at
all.

Given the above, I request the authors to replace:

   A technique to unicast packets to the root of a P2MP or MP2MP LSP
   is documented in [I-D.rosen-l3vpn-mvpn-mspmsi] section 3.2.2.1 and
   [I-D.ietf-mpls-ldp-p2mp] section 3.

with:

     A technique to unicast packets to the root of MP2MP LSP is
     documented in [I-D.ietf-mpls-ldp-p2mp] section 3 (where the root
     would advertise in LDP its unicast FEC).

If the authors insist on using MVPN S-PMSI auto-discovery routes, then
can they please justify the reason for using such routes? If there are
indeed valid reasons for using such routes then the above text should be
replaced with:

    A technique to unicast packets to the root of MP2MP LSP using
    MVPN S-PMSI auto-discovery routes
    [I-D.draft-ietf-l3vpn-2547bis-mcast-bgp] is for the root to
    originate a "wildcard" S-PMSI auto-discovery route with the
    Tunnel Type of the PMSI Tunnel attribute set to Ingress
    Replication.

    A technique to unicast packets to the root of MP2MP LSP without
    relying on MVPN S-PMSI auto-discovery routes is documented in
    [I-D.ietf-mpls-ldp-p2mp] section 3 (where the root would advertise
    in LDP its unicast FEC)."

Yakov.