[RTG-DIR] RtgDir review: draft-kompella-l2vpn-l2vpn-07.txt

["Bocci, Matthew (Matthew)" <[e-mail]>]

Hello,

I have been selected as the Routing Directorate reviewer for this draft. The Routing Directorate seeks to review all routing or routing-related drafts as they pass through IETF last call and IESG review. The purpose of the review is to provide assistance to the Routing ADs. For more information about the Routing Directorate, please see http://www.ietf.org/iesg/directorate/routing.html

Although these comments are primarily for the use of the Routing ADs, it would be helpful if you could consider them along with any other IETF Last Call comments that you receive, and strive to resolve them through discussion or by updating the draft.

Document: draft-kompella-l2vpn-l2vpn-07.txt
Reviewer: Matthew Bocci
Review Date: 26-09-11
IETF LC End Date: 26-09-11
Intended Status: Informational

Summary:

I have some major concerns about this document, and some minor concerns that I think should be resolved before the document is published.


Comments:

Major Issues:

- Relationship to published and on-going work in the L2VPN and PWE3 working groups. This draft describes an alternative to the procedures for signalling PW labels used in pt-pt layer 2 VPNs (VPWS) and for auto-discovery of endpoints participating in a L2VPN. The existing IETF-approved technologies use LDP for the signalling (as described in RFC4447) and a combination of that with BGP for auto-discovery (RFC6074). Since this draft describes an alternative that was rejected by the L2VPN WG, I would suggest adding a disclaimer to the abstract and introduction, as per the recommendation of RFC5742, along the lines of "The IETF technology for this function is specified in RFC6074 and RFC4447", in addition to the suggestions on the list that implementations of this draft must also comply to these RFCs.

- Section 9: IANA Considerations. This section requests a registry be created with standards action code points. I believe this is not appropriate as this is an informational draft. There has already been some discussion on this point on the list, and that is noted as a part of this review.

- Section 5: Layer 2 VPN interworking. This section introduces a layer 2 transport service for IP packet. However, just encapsulating IP packets between PEs will not be sufficient for a layer 2 VPN service between the CEs. You also need to support something to allow L2 address resolution between the CEs, for example translation of the neighbour discover protocols (e.g. ARP over Ethernet and InvARP over FR). Since this is describing the L2VPN, and not just the PW encapsulation, I think this section should either say how this is done with BGP (draft-ietf-l2vpn-arp-mediation uses LDP) or just say it is out of scope of this particular draft and the L2 address is statically configured.



Minor Issues:

General:
- The draft mainly discussed pt-pt L2VPNs. The general term for this is VPWS, but this term is not mentioned anywhere. It would help to clarify with a statement in the introduction that this the subject of the draft.

- It would help if the figures showing the TLV structures showed the detailed structure, throughout, including bit fields, etc, in line with common practice in IETF RFCs.



- 1. Introduction, 5th paragraph:
"Technically, the approach proposed here uses the concepts and
   solution and described in [RFC4761], which describes VPLS, a
   particular form of a Layer 2 VPN."

This reads as if RFC4761 is *the* description of VPLS. This is not the case and the IETF has standardised two VPLS methods. I propose modifying this to "…which describes a method for VPLS,…".

- 1.1 Terminology. Final paragraph.
   "These will be referred to as Attachment
   Circuits (ACs), following [RFC4447].  Similarly, the entity that
   connects two attachment circuits across the Service Provider network
   is called a pseudo-wire (PW)."

RFC3985 is probably the correct reference.
Also:
 s/pseudo-wire/pseudowire

- 1.2.5: PE Scaling
This section spends a lot of time discussing the scaling issues of L3 VPNs. I am not sure why this is required in a BGP L2VPN draft, unless the issue is that because the control plane is the same, many of the same scaling considerations apply. Please can you clarify if this is true, and if so make such a note in the text?

- 1.3: Advantages of Layer 3 VPNs
I do not think this adds any value to a draft on L2 VPNs. The content may be useful elsewhere, but I think it would be better if this was removed from this draft.

- 3: Operation of Layer 2 VPNs
"In what follows, Frame Relay serves as the Layer 2 medium, and each
   CE has multiple DLCIs to its PE, each to connect to another CE in the
   VPN.  If the Layer 2 medium were ATM, then each CE would have
   multiple VPI/VCIs to connect to other CEs. "

I think I know what you mean by "medium" I.e. The underlying link layer, where each group of DLCIs is an AC in the RFC3985 sense, plus DLCI acts as a demarkation of a L2VPN service between the PE and CE. If so, I think it would help to add this clarification.

- 6.3: IP-Only Layer 2 Interworking:

         +----------------------------+
         | Tunnel |  VPN  |    IP     |     VPN label is the
         | Encap  | Label |  Packet   |     demultiplexing field
         +----------------------------+

          Figure 3: Format of IP-only Layer 2 interworking packet

I think the field marked "Tunnel Encap" should instead be labelled "PSN Transport Header" or "MPLS Transport Header", in common with the other encapsulation RFCs that you have referenced.


Best regards

Matthew