Re: [bess] Poll for early allocation request for draft-ietf-bess-mvpn-evpn-aggregation-label

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

Hi Jingrong,

Please see zzh2> below.

From: BESS <[e-mail]> On Behalf Of Xiejingrong
Sent: Wednesday, December 12, 2018 9:24 PM
To: Jeffrey (Zhaohui) Zhang <[e-mail]>; [e-mail]; [e-mail]
Subject: Re: [bess] Poll for early allocation request for draft-ietf-bess-mvpn-evpn-aggregation-label


s/inter-area/intra-area/g

From: Xiejingrong
Sent: Thursday, December 13, 2018 10:22 AM
To: 'Jeffrey (Zhaohui) Zhang' <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: RE: Poll for early allocation request for draft-ietf-bess-mvpn-evpn-aggregation-label

Hi Jeffrey,

Let me take the section 2.2.3 for explaination:

   In summary, labels can be allocated and advertised the following
   ways:

   1.  A central authority allocates per-VPN/BD/ES labels from the DCB.
       PEs advertise the labels with an indication that they are from
       the DCB.

   2.  A central authority allocates per-VPN/BD/ES labels from a few
       common context label spaces, and allocate labels from the DCB to
       identify those context label spaces.  PEs advertise the VPN/BD
       labels along with the context-identifying labels.

   3.  A central authority assigns disjoint label blocks from those a //
       few context label spaces to each PE, and allocate labels from the
       DCB to identify the context label spaces.  Each PE allocates
       labels from its assigned label block independently for its
       segmented S-PMSI, along with the context-identifying labels.

   Option 1 is simplest, but it requires that all the PEs set aside a
   common label block for the DCB that is large enough for all the
   VPNs/BDs/ESes combined.  Option 3 is needed only for segmented
   selective tunnels that are set up dynamically.  Multiple options
   could be used in any combination depending on the deployment
   situation.

Option-1 is simplest and I like it very much (anyone who don't like simplification?). For Inter-area EVPN deployment scenarios, it is strong and simple enough I think.

Zzh2> So I assume you're not objecting to the early allocation for DCB-flag at least?

But when it is not the suitable case, and Option-2 has to be used, I think things are becoming complex: You still need a DCB from 'main/default' label-space, though this DCB is very small, which maybe only include ONE label. And then the ONE label is used as 'context-label'. While for BIER case, BIER header itself can act as a 'BIER-Context' naturally. Am I understanding correctly ?

Zzh2> Nowadays with the adoption of SR, allocating SAME SRGBs across routers is not difficult and is the preferred way. If you use DCB (could just be the SRGB itself) for non-segmented case, what's the concern with allocating a context label from the DCB/SRGB? See later comment about BIER-context.

For Option-3, I do understand it as two sub-options, Option-3a if there is enough number of Labels in the DCB, and Option-3b if there isn't and the ONE 'DCB' label is used as context-label. Each one is difficult for me to consider the development and deployment. One the other hand, the segmented MVPN can use the 'UMH' mechanism to select the right upstream-assigned VpnLabel to download to forwarding states.

Zzh2> There is no 3a. There could be multiple DCB labels for multiple context label spaces, either because of scaling requirement (in theory) or for whatever reason an operator wants to use multiple.
Zzh2> I don't think selectively installing upstream assigned labels based on UMH is good enough (and it introduces more complexity). The sources could be everywhere, and in case of EVPN, the forwarding could be (*,g) based, so you'll end up with the original problem.

So my summarized comments:
DCB is similar to VNI very much, but the MPLS labels in the "main/default" space is very costly due to the 'per-platform' (RFC5331) allocation.

Zzh2> If one can do common SRGB for SR, then one can do DCB for MVPN/EVPN. If you're still concerned with that, you can have a separate context label space for EVPN/MVPN purpose, with the context label from the DCB/SRGB. I don't want to tie it to BIER only though, because the problem and solution equally applies to P2MP tunnels.

DCB is similar to SRGB very much, but DCB requires 'absolute' unique value other than the 'unique' index in SRGB(at least has such mechanism).

Zzh2> Practically, operators strongly desire to use common SRGBs. Vendors had resisted the push for using common SRGBs but now have given up.

Use of context-label from a DCB can be comparable to the use of the 'BIER-specific' context in case of BIER.

Zzh2> There is no need, and it is not desired to have a BIER-specific context. Besides, defining a new BIER header's "proto" value to indicate a subsequent context label space should first be discussed in BIER WG; if that passes, then we come back to (or at least involve) BESS WG to enhance MVPN/EVPN signaling so that every PE knows where to allocate labels and where to install forwarding state.

Use of 'dynamic' allocation with DCB mechanism in segmented MVPN deployment may add extra complexity.

Zzh2> Compared to existing method of using upstream assigned labels, what is the complexity? Upstream assigned labels are assigned from the assigner's main/default label space; the "dynamic" allocation scheme in option-3 allocates from a label block (of a context label space identified by a DCB label) assigned to the assigner. If the need to maintain that extra label block information is complicated, wouldn't it be more complicated to selectively install upstream-assigned labels based on UMH selection (forget about that it would not work all the time)?

Zzh> If that is not convincing enough, what is a better solution? I know you have proposed doing IP lookup - we discussed in a separate thread on the pros/cons of that and we're working together on a separate draft on that, right? I also have a short section 2.2.2.3 on that.

I suggest this draft to make more clear what the use cases are, what it really want to solve, and what it don't.

Zzh2> The use cases and problem domains are discussed in section 2.1, and more complicated scenarios are followed-up in section 2.2.
Zzh2> About "what it don't" - can you point out the areas that you think this draft should cover or explicitly declare out of scope?
Zzh2> Thanks.
Zzh2> Jeffrey


Thanks.
Jingrong



From: Jeffrey (Zhaohui) Zhang [mailto:[e-mail]]
Sent: Wednesday, December 12, 2018 10:42 PM
To: Xiejingrong <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: RE: Poll for early allocation request for draft-ietf-bess-mvpn-evpn-aggregation-label

Jingrong,

Please see zzh> below.

From: BESS <[e-mail]<mailto:[e-mail]>> On Behalf Of Xiejingrong
Sent: Tuesday, December 11, 2018 8:14 PM
To: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: Re: [bess] Poll for early allocation request for draft-ietf-bess-mvpn-evpn-aggregation-label

Objection.

Zzh> Please note that this is not a LC for the draft. This is the poll for early allocation for the DCB-flag and an extended community type.

I remember I have raised my concerns, but I didn't find the response.

Zzh> Sorry for missing those. Please see below.

Copy the concerns I have listed before:

1.   The problem stated by this draft is valid, and the proposed method is useful for some of the listed problem. For example, EVPN BUM who uses MPLS identification and dataplane.
Zzh> Do you think the proposed solution is reasonable for the problems? If so, we would like to see early allocation is done. The allocation is temporary - it would time out after some time if the draft does not become a RFC.

2.   EVPN BUM using vxlan/vni identification may not need a MPLS label to identify the vpn/tenant.
Zzh> The draft is about "aggregation label", so vxlan/vni is irrelevant. On the other hand, in case of vxlan/vni, the VNI is no different from a DCB label in concept (so the solution of using DCB label should be reasonable).

3.   For MVPN who has a UMH(Upstream Multicast Hop) selection procedure, the exist using of upstream-assigned VpnLabel can be optimized to only populate to forwarding-state when there are c-multicast flows selecting the specific UMH PE.
Zzh> If that is a better solution, perhaps a separate draft can be written. The solution in this draft is simpler and in concept no different from vxlan case.

4.   For an End-to-End deployment of MVPN who spans multi-ASes as the way stated in <draft-geng-bier-sr-multicast-deployment>, the allocation of a global-unique label is useful and possible. But operators may need to be very careful to allocate the very limited MPLS labels. Because, MPLS labels has been divided to SRLB and SRGB, and SRGB may have been again divided by SR-domains according to <draft-filsfils-spring-large-scale-interconnect-12>.
Zzh> What's relevant here is the second part of your text above (the "But operators ...") - though that is the same point #5 below (please see my response below).

5.   For segmented MVPN deployment, the further divide of the MPLS Label is also difficult when thinking of the above.
Zzh> Please see section 2.2.2 of this draft.

6.   For BIER, is the BIER proto=1 indicating a BIER-specific unique VpnLabel ? or a Per-platform (RFC5331) downstream-assigned unique label ?  if it is the later one, how about adding a new BIER proto value to indicating a BIER-specific unique VpnLabel ?  And then a static Context (BIER) can be optional to the dynamic advertising of a Context ?
Zzh> In BIER header, proto=1 indicates downstream-assigned label. There is no need to define a new BIER specific proto value. The reason is that "downstream-assigned label" just means that it is a label in the "main/default" label space of the receiving router, and a DCB label is just that. Nothing is BIER specific here. I believe Tony also responded to you (and in BIER WG).
Zzh> Thanks!
Zzh> Jeffrey

Jingrong


From: BESS [mailto:[e-mail]] On Behalf Of [e-mail]<mailto:[e-mail]>
Sent: Tuesday, December 11, 2018 11:10 PM
To: [e-mail]<mailto:[e-mail]>
Subject: [bess] Poll for early allocation request for draft-ietf-bess-mvpn-evpn-aggregation-label

Hi WG,

We have received an early allocation request for the draft-ietf-bess-mvpn-evpn-aggregation-label.

Please raise your concerns if you object to this request and if you think that the document is not mature enough.
Feel also free to support this request.

We will wait until next Monday (12/17) to gather feedbacks.

Thanks,

Stephane



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