[mpls] Last Call comments on ldp upstream label allocation

[Eric Rosen <erosen at cisco.com>]

I have a couple of comments on draft-ietf-mpls-ldp-upstream-04.

The draft has a normative reference to RFC 3472 "Generalized Multi-Protocol
Label Switching (GMPLS) Signaling Constraint-based Routed Label Distribution
Protocol (CR-LDP) Extensions".  I don't think this is allowable, as we do
not want to take any action that prevents the deprecated CR-LDP documents
from being reclassified as historic.

Section 4.3 of RFC 3468 "The Multiprotocol Label Switching (MPLS) Working Group
decision on MPLS signaling protocols" says:

   Consequently we need to keep CR-LDP referenceable, i.e., on the
   standards track, for the foreseeable future.  The implication of this
   is not that we need to progress it further, or need to undertake
   further work in the area.  One implication however is that standards
   organizations which reference the document, need to be notified of
   our decision so that they (at their own pace) can change their
   references to more appropriate documents.

I would interpret this as implying that the IETF should not be creating
normative references to CR-LDP documents.  (If we expect other organizations
to be changing their references to the CR-LDP documents, we shouldn't be
creating new references to them.)  Note that RFC 3468 explicitly calls out
RFC 3472 as one of the deprecated documents.

The normative reference is due to the draft's reuse of the "Interface ID
TLV" defined in RFC 3472.  If this TLV is to be used, it would be better to
define it in the ldp-upstream draft and to have IANA change the reference in
the iana.org registry.

However, it is questionable whether the Interface ID TLV is really the right
TLV for ldp-upstream to use, as the interface ID TLV has fields that are do
not appear to be needed in ldp-upstream (e.g., "next/previous hop", "logical
inteface id").

One more comment: the "LDP Tunnel Identifiers" defined in section 5 of
ldp-upstream do not appear to be exactly the same in all cases as the "PMSI
Tunnel Attribute Tunnel Identifiers" defined in section 5 of draft-ietf-
l3vpn-2547bis-mcast-bgp-08.txt.  (E.g., the means of identification of
RSVP-TE tunnels seems to be different.)  Perhaps ldp-upstream should simply
reference the PMSI tunnel attribute tunnel ids defined in the latter
document.