RE: [mpls] Last Call: <draft-ietf-mpls-ldp-ipv6-14.txt> (Updates to LDP for IPv6) to Proposed Standard

Hi Adrian and all,
I was the one who raised the interop issues we found while testing our implementation of LDP IPv6 against existing and deployed implementations. I proposed a simple method of using the existing FEC advertisement capability at the session level as a way for an LSR to detect if an implementation support LDP IPv6 FECs and IPv6 addresses. This existing FEC advertisement capability at session level is defined in draft-ietf-mpls-ldp-ip-pw-capability-08 but with the limitation that it can be used only to disable support of IPv6 FECs in LDP Initialization Message; we proposed to generalize the method to also indicate explicit support for IPv6 FECs and IPv6 Addresses in LDP Initialization Message.  This method is safe and was also used with mLDP P2MP and MP2MP FECs when they were introduced. The intent here is that all session level capabilities in LDP should follow RFC 5561 approach.

There was an individual contributor which supported the proposal on the mailing list but the authors chose to ignore it and went with a proposal which overloaded the meaning of the dual-stack capability TLV. Regardless of the merit of either method, the discussion on the MPLS mailing list was not closed properly from my perspective.

Now here is the concern I raised with using the dual-stack capability. Not only this TLV is an adjacency level feature which is has nothing to do with FEC capability advertisement, but it is introducing complexity in the implementation which now has to check dual-stack capability for *each* adjacency to the peer *and* the session level FEC capability to decide what the peer is capable of at the *session level*.

Having said that, I want to keep the spirit of cooperation and make sure we get this draft published. To that effect, I am not opposed to its publication as long as the following points are clarified in the draft since now FEC capability of the LSR peer is determined by a check a both adjacency and session levels:

1. The draft is missing the behavior when multiple adjacencies exist to the same LSR and the peer LSR advertised the dual-stack capability only over a subset of these Hello adjacencies. 
I assume here the peer LSR is considered to be dual-stack capable as soon as any of the Hello adjacencies includes the dual-stack capability. This would allow a hitless upgrade scenario from an older implementation to one which complies to this draft

2. Similarly, what would be the behavior if a hello adjacency changes from sending the dual-stack capability to not sending it? This would be for example in a hitless downgrade to a version of LDP which does not comply to this draft. 
I assume here that the session must be bounced since the LSRs need a clean state to not send IPv6 addresses and IPv6 FECs. 

3. The document defines 2 values for the dual-stack capability TR. It does not mention the behavior when an unknown value is received.   
Will that be considered a fatal error?

4. The draft is missing the behavior of when the peer LSR does not advertise the dual-stack capability in all the Hello adjacencies but it advertised the enabling or disabling of the IPv6 prefix FEC capability in the session initialization message. 
I assume here that the absence of the dual-stack capability overrides any session level IPv6 FEC prefix capability advertisement. 

5. The draft is missing the behavior of when the peer LSR does not advertise the dual-stack capability in all the Hello adjacencies but it advertised the enabling of the IPv6 prefix FEC capability in the session Capability message.
I assume the same behavior as in (4) applies here.

Regards,
Mustapha.

> -----Original Message-----
> From: mpls [mailto:mpls-bounces@ietf.org] On Behalf Of The IESG
> Sent: Thursday, December 04, 2014 2:37 PM
> To: IETF-Announce
> Cc: mpls@ietf.org
> Subject: [mpls] Last Call: <draft-ietf-mpls-ldp-ipv6-14.txt> (Updates to LDP for IPv6)
> to Proposed Standard
> 
> 
> The IESG has received a request from the Multiprotocol Label Switching WG
> (mpls) to consider the following document:
> - 'Updates to LDP for IPv6'
>   <draft-ietf-mpls-ldp-ipv6-14.txt> as Proposed Standard
> 
> The IESG plans to make a decision in the next few weeks, and solicits final
> comments on this action. Please send substantive comments to the ietf@ietf.org
> mailing lists by 2014-12-18. Exceptionally, comments may be sent to iesg@ietf.org
> instead. In either case, please retain the beginning of the Subject line to allow
> automated sorting.
> 
> Abstract
> 
>    The Label Distribution Protocol (LDP) specification defines
>    procedures to exchange label bindings over either IPv4, or IPv6 or
>    both networks. This document corrects and clarifies the LDP behavior
>    when IPv6 network is used (with or without IPv4). This document
>    updates RFC 5036 and RFC 6720.
> 
> The file can be obtained via
> http://datatracker.ietf.org/doc/draft-ietf-mpls-ldp-ipv6/
> 
> IESG discussion can be tracked via
> http://datatracker.ietf.org/doc/draft-ietf-mpls-ldp-ipv6/ballot/
> 
> 
> No IPR declarations have been submitted directly on this I-D.
> 
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