I have been selected as the General Area Review Team (Gen-ART)
reviewer for this draft (for background on Gen-ART, please see
http://www.alvestrand.no/ietf/gen/art/gen-art-FAQ.html).
Please resolve these comments along with any other Last Call comments
you may receive.
Document: draft-ietf-l3vpn-2547bis-mcast-bgp-07
Reviewer: Spencer Dawkins
Review Date: 2009-09-17 (oops!)
IETF LC End Date: 2009-09-08
IESG Telechat date: (not known)
Summary: This draft is almost ready for publication as a Proposed Standard.
I have some comments, mostly 2119 language plus some sentences that didn't
parse and seemed important.
Abstract
This document describes the BGP encodings and procedures for
exchanging the information elements required by Multicast in MPLS/BGP
IP VPNs, as specified in [MVPN].
Spencer (nit): I'd expect the RFC Editor to remove a reference in the
Abstract section.
2. Introduction
This document describes the BGP encodings and procedures for
exchanging the information elements required by Multicast in MPLS/BGP
IP VPNs, as specified in [MVPN]. This document assumes a thorough
familiarity with procedures, concepts and terms described in [MVPN].
This document defines a new NLRI, MCAST-VPN NLRI. The MCAST-VPN NLRI
Spencer (nit): I'd expect the RFC Editor to ask that abbreviations be
expanded on first use.
is used for MVPN auto-discovery, advertising MVPN to I-PMSI tunnel
binding, advertising (C-S, C-G) to S-PMSI tunnel binding, VPN
customer multicast routing information exchange among PEs, choosing a
single forwarder PE, and for procedures in support of co-locating a
C-RP on a PE.
5. PMSI Tunnel attribute
When a router that receives a BGP Update that contains the PMSI
Tunnel attribute with its Partial bit set determines that the
attribute is malformed, the router SHOULD treat this Update as though
all the routes contained in this Update had been withdrawn.
Spencer (minor): why SHOULD in this case, and not MUST? (Note that similar
text occurs throughout this section)
An implementation MUST provide debugging facilities to permit issues
caused by malformed PMSI Tunnel attribute to be diagnosed. At a
minimum, such facilities SHOULD include logging an error when such an
attribute is detected.
Spencer (minor): If debugging facilities are a MUST, shouldn't the minimum
debugging facility be a MUST? :-) Or are there well-understood reasons
("MUST do X unless") that could be provided? (Note that similar text occurs
elsewhere in the draft)
The PMSI Tunnel attribute is used in conjunction with Intra-AS I-PMSI
A-D routes, Inter-AS I-PMSI A-D routes, S-PMSI A-D routes, and Leaf
A-D routes.
7. VRF Route Import Extended Community
If a PE uses Route Target Constrain [RT-CONSTRAIN], the PE SHOULD
advertise all such C-multicast Import RTs using Route Target
Constrains (note that doing this requires just a single Route Target
Constraint advertisement by the PE). This allows each C-multicast
route to reach only the relevant PE. To constrain distribution of the
Route Target Constrain routes to the AS of the advertising PE these
routes SHOULD carry the NO_EXPORT Community ([RFC1997]).
Spencer (minor): I'm not sure I understand why these are SHOULDs and not
MUSTs. (Note that similar text occurs elsewhere in the draft) I note that
you give reasons why the similar text in Section 8 is not a MUST, using this
explanation:
"Note that if non-segmented inter-AS P-tunnels are being used, then
the Intra-AS I-PMSI routes need to be distributed to other ASes and
MUST NOT carry the NO_EXPORT community."
8. PE Distinguisher Labels Attribute
The Next Hop field of the MP_REACH_NLRI attribute of the route SHOULD
be set to the same IP address as the one carried in the Originating
Router's IP Address field.
Spencer (minor): I'm not sure why this is a SHOULD and not a MUST, but if it
is a SHOULD, I'd expect to see some guidance about what happens if it's not
observed - does the mechanism still work?
10. Non-congruent Unicast and Multicast Connectivity
It is possible to deploy MVPN such the multicast routing and the
Spencer (minor): is this "such that"? This is probably a nit but I'm having
to guess at the parsing.
unicast routing are "non-congruent". For instance, the CEs may be
distributing to the PEs a special set of unicast routes that are to
be used exclusively for the purpose of upstream multicast hop
selection, and not used for unicast routing at all. (For example,
when BGP is the CE-PE unicast routing protocol, the CEs may be using
SAFI 2 ("Network Layer Reachability Information used for multicast
forwarding" [IANA-SAFI]), and either IPv4 or IPv6 AFI to distribute a
special set of routes that are to be used for, and only for, upstream
multicast hop selection.) In such a situation, we will speak of the
MVPN as having two VRFs on a given PE, one containing the routes that
are used for unicast, the other containing the unicast routes that
are used for upstream multicast hop (UMH) selection. We will call the
former the "unicast routing VRF", and the latter the "UMH VRF"
(upstream multicast hop VRF).
11.4. C-multicast routes aggregation
Further a BGP receiver, that receives multiple such routes with the
same NLRI for the same C-multicast route, will potentially create
forwarding state based on a single C-multicast route. As per the
procedures described in Section "Receiving C-Multicast Routes by a
PE", this forwarding state will be the same as the state that would
have been created based an other route with same NLRI.
Spencer (nit): I'm pretty sure this is "based on another route" - but it
doesn't parse for me without help.
12.1. Originating S-PMSI A-D routes
In all of the above cases an implementation MUST allow to modify the
default via configuration.
Spencer (minor): sorry, this doesn't parse. I'm guessing it's missing a
noun, but I can't suggest text.
16.1.1. Dampening withdrawals of C-multicast routes
+ Until the withdrawls are actually sent, multicast traffic for the
Spencer (nit): s/withdrawls/withdrawals/g, because I saw other occurances in
the document...
C-multicast routes in question will be continued to be
transmitted to the PE, which will just have to discard it. Note
that the PE may receive useless (multicast) traffic anyway,
irrespective of dampening of withdrawals of C-multicast routes
due to the use of I-PMSIs.
17. Security Considerations
The mechanisms described in this document could re-use the existing
BGP security mechanisms.
Specer (minor): "could" seems awfully nebulous for security considerations
:-) I'm guessing you could delete this sentence, but it needs help of some
sort.
18. IANA Considerations
Spencer (minor): I see from the ID tracker that IANA has already asked for
clarification on registration procedures ... :-)
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