Re: [mpls] Solicit Opinions on Definition of MPLS Global Label

["Jeffrey (Zhaohui) Zhang" <[e-mail]>]

Zhenbin,

Your draft says:

   The context-specific label can solve the issue of aggregating
   multiple MVPNs or VPLS instances over a single P2MP LSP.  But if the
   MP2MP LSP is adopted for aggregating multiple MVPN/VPLS instances the
   solution does not work since there are multiple root PEs which may
   allocate the same context-specific label for different MVPN/VPLS
   instances.

I don't think there is a real difference between the p2mp and mp2mp. In either case, the vpn-identifying label is "upstream-allocated" by the root of the tunnel and the receiving PEs will interpret that in the context of the root. In case of mp2mp, that means an ingress PE will use vpn-identifying labels assigned by the root (may be different from itself). In case of p2mp, it is also "root-assigned", it's just that the root happens to be the ingress PE itself.

In the mp2mp case, it is true the root may not be a PE; but the root can certainly advertise PMSI routes to advertise the labels for PEs to use. That is control plane and for label advertisement only - it does have CE sites to send/receive traffic to/from. Compare to other ways of coordinating what label to use, this is simple and straightforward.

Jeffrey

From: Jeffrey (Zhaohui) Zhang
Sent: Thursday, November 05, 2015 4:26 AM
To: 'Lizhenbin' <[e-mail]>; [e-mail]
Subject: RE: [mpls] Solicit Opinions on Definition of MPLS Global Label

Zhenbin,

   -- For MPLS upstream label assignment in context-specific label
   space, all downstream nodes can understand the meaning of the label
   allocated by the upstream node binding for specific MVPN/VPLS
   instance.  We can see the root PE as one type to central controlled
   node to allocate label to all leaf nodes.  And thinking about the
   uniqueness of the context determine by the shared P-tunnel, these
   labels in fact are also unique in the network.  Should they belong to
   global label?

These are "context-specific", not global. Different upstream nodes can assign the same label value for different meanings, and whoever receives those labels in packets need to interpret the labels in the specific context for the assigner.

Jeffrey

From: Lizhenbin [mailto:[e-mail]]
Sent: Wednesday, November 04, 2015 2:27 PM
To: [e-mail]<mailto:[e-mail]>
Subject: [mpls] Solicit Opinions on Definition of MPLS Global Label


Hi MPLSers,

As the development of MPLS technologies, many new label concepts beyond RFC3031 are proposed. And in segment routing MPLS label can be

allocated and flooded in the network which means the meaning of the lablel can be understood by all nodes in the network. It is totally different from

the label distribution behavior of LDP, RSVP-TE, and MP-BGP. From my point of view we need not argue if it is global label or global ID. In fact, the

possible persons who read the drafts of protocol extensions for segment routing which incorporate the label allocation may be confused that MPLS WG as

the base of MPLS work seems to have nothing with the work. But the challenge of definition of global label truly exists which has been proposed in the draft

https://www.ietf.org/id/draft-li-mpls-global-label-usecases-03.txt. Hope you can refer to Section 4 of the draft.

The debates on MPLS global label have lasted for a long time. The opinions can be classified as following:

Opinion 1: Segment Routing has nothing with global label and please do not make it bother MPLS WG. But it seems a little hard to convince some MPLSers.

Opinion 2: The usecase truly exists. But the concept of global label is too big. It is hard to allocate a label which is unique spanning multiple domains or

as IP address which is unique all over world since it is not a scalable way or it is hard to achieve the goal. Then maybe it is a better way to narrow the

scope to rename the global label as Domain-wide label, Network-wide label, etc.

Opinion 3: The global label can be kept to cover more label concepts which label behaviors in the control plane and forward plane are different form the

traditional LDP/RSVP-TE/MP-BGP.

Since I could not get more time in my presentation to collect your opinions, if convenient please help feedback your opinion in your mailing list. Hope through

the discussion we can make some consensus.

Best Regards,

Zhenbin(Robin)