Hi Ali and Sasha,
Let’s use VLAN-aware bundle to clarify why we need both Access VNI (LSI) and
Core VNI in one VxLAN header.
In traditional VLAN-aware bundle ([RFC7432]), multiple VIDs map to a single
EVI. Isolation relies on VIDs (e.g., VID 10 vs. 20) to separate broadcast
domains, even with overlapping MACs.
In our Layer 3 scenario (LSI-aware bundle, the L3 equivalent), VIDs are
replaced by LSIs (Access VNIs) to retain that "broadcast domain ID" role, while
the core EVI maps to a Core VNI.
If we only include Core VNI (no LSI), the core PE loses the LSI (like losing
VID) and can’t distinguish traffic from overlapping MACs in shared Core
VNI—breaking isolation, just as losing VID would in VLAN-aware bundle.
Since standard VxLAN has only one VNI field, we extend it to carry both: Core
VNI (for EVI) and LSI (for "VID-like" isolation).
Best regards,
Wei
原始邮件
发件人：Ali Sajassi (sajassi) <[email protected]>
发件时间：2025年8月1日 00:59
收件人：Wei Wang <[email protected]>, Aijun Wang
<[email protected]>, 'Alexander Vainshtein'
<[email protected]>, [email protected] <[email protected]>,
[email protected]
<[email protected]>
主题：[bess] Re: My question/comment about draft-wang-bess-l3-accessible-evpn-10
at the BESS WG session today
Wei,
You said: "the critical challenge lies in how to physically encapsulate
both in a single VxLAN packet to ensure end-to-end traffic isolation and
correct mapping in a Layer 3 access scenario, which is not addressed by
existing specifications.”
Please elaborate - i.e., give detailed explanation and use cases as to why both
VNI need to be encapsulated in the same VxLAN packet. PWs are only stretched
over access network (and NOT core network) and are terminated onto service VRF.
Therefore, they are not needed between VRFs over the core network!
Cheers,
Ali
From: Wei Wang <[email protected]>
Date: Wednesday, July 30, 2025 at 6:34 PM
To: Ali Sajassi (sajassi) <[email protected]>, Aijun Wang
<[email protected]>, 'Alexander Vainshtein'
<[email protected]>, [email protected] <[email protected]>,
[email protected]
<[email protected]>
Subject: Re: [bess] Re: My question/comment about
draft-wang-bess-l3-accessible-evpn-10 at the BESS WG session today
Hi Ali,
Thanks for your perspective. While we agree that the access EVPN-VPWS VNI and
backbone VxLAN VNI are logically independent in terms of their roles—similar to
MPLS labels or Q-tags—the critical challenge lies in how to physically
encapsulate both in a single VxLAN packet to ensure end-to-end traffic
isolation and correct mapping in a Layer 3 access scenario, which is not
addressed by existing specifications.
Our proposal addresses this by extending the VxLAN header with an "S" flag and
a 16-bit LSI field. When the "S" flag is set, the LSI field carries the access
PW VNI, while the original VNI field retains the backbone VNI—enabling both
identifiers to coexist in one packet . This extension is precisely to bridge
the gap between logical independence and practical encapsulation requirements
in Layer 3 access scenarios.
Best Regards,
Wei
原始邮件
发件人：Ali Sajassi (sajassi) <[email protected]>
发件时间：2025年7月26日 01:03
收件人：Aijun Wang <[email protected]>, 'Alexander Vainshtein'
<[email protected]>, [email protected] <[email protected]>,
[email protected]
<[email protected]>
主题：[bess] Re: My question/comment about draft-wang-bess-l3-accessible-evpn-10
at the BESS WG session today
Hi Aiju,
The answer to your question is very easy. The access EVPN-VPWS VNI
(representing a PW) is independent from the backbone EVPN VxLAN VNI
representing ELAN, E-TREE, or IRB service just like the access MPLS label for
PW is independent from backbone EVPN MPLS label representing ELAN, E-TREE, or
IRB service, just like Q-tag or Q-in-Q tag in the access is independent from
VNI or MPLS label in the backbone.
You should keep in mind that VNI does NOT need to be global. It can be domain
specific and even down-stream assigned!
Cheers,
Ali
From: Aijun Wang <[email protected]>
Date: Friday, July 25, 2025 at 1:50 AM
To: Ali Sajassi (sajassi) <[email protected]>, 'Alexander Vainshtein'
<[email protected]>, [email protected] <[email protected]>,
[email protected]
<[email protected]>
Subject: RE: [bess] Re: My question/comment about
draft-wang-bess-l3-accessible-evpn-10 at the BESS WG session today
Hi, Ali:
It’s relatively easy to incorporate the MPLS based pseudowire into EVPN, as
that described in RFC9784.
But, it is not easy to incorporate the VxLAN based PW into EVPN, although they
are all VPWS.
draft-wang-bess-l3-accessible-evpn wants just to fit the gap.
Or else, would you like to tell us how to encapsulate the access PW VNI
information, together with the backbone VxLAN VNI information in the normal
VxLAN packet?
Best Regards
Aijun Wang
China Telecom
From: [email protected] <[email protected]> On
Behalf Of Ali Sajassi (sajassi)
Sent: Friday, July 25, 2025 1:10 AM
To: Aijun Wang <[email protected]>; 'Alexander Vainshtein'
<[email protected]>; [email protected];
[email protected]
Subject: [bess] Re: My question/comment about
draft-wang-bess-l3-accessible-evpn-10 at the BESS WG session today
Sasha,
Thanks for your question as I couldn’t figure out what this draft was trying to
do on my quick glance ☺
Aijun,
EVPN-VPWS (RFC8214) applies to both MPLS and VxLAN as described in the
document. Furthermore, although RFC9784 is written with MPLS access network as
an example, it can easily be applied to VxLAN access since a VPWS instance can
be either per RFC8214.
So, in light of these two RFCs, are there anything that you want to do that is
not covered by these two RFCs?
Cheers,
Ali
From: Aijun Wang <[email protected]>
Date: Thursday, July 24, 2025 at 10:54 AM
To: 'Alexander Vainshtein'
<[email protected]>,
[email protected] <[email protected]>,
[email protected] <[email protected]>
Subject: [bess] Re: My question/comment about
draft-wang-bess-l3-accessible-evpn-10 at the BESS WG session today
Hi, Sasha:
Using the concept of virtual segment in RFC 9784 to access the core EVPN
service is similar with our proposal.
The difference is that in RFC 9784, the access network is one MPLS based
network, the PW can be identified by the corresponding MPLS label.
But, in our proposal, the access network is one Layer 3 Native IP network,
there is no MPLS deployed in the access network.
Then, some new solution (especially how to identify the logical session, how to
transfer them via the control plane and how to encapsulate them in the VxLAN
packet should be defined.
Does the above explanation address your concerns?
If so, we can add some procedure description for our proposal according to
another expert’s comments.
Thanks!
Best Regards
Aijun Wang
China Telecom
From: [email protected] <[email protected]> On
Behalf Of Alexander Vainshtein
Sent: Thursday, July 24, 2025 5:48 PM
To: [email protected]; [email protected]
Subject: [bess] My question/comment about
draft-wang-bess-l3-accessible-evpn-10 at the BESS WG session today
Hi all,
Just to repeat my question/comment asked at the BESS WG session in Madrid today:
I have asked whether the authors considered using the PWs crossing the L3
domains as Virtual Ethernet Segments as described in Section 1.3 of RFC 9784?
At the first glance, this could address all the problems with which this draft
tries to cope.
Regards,
Sasha
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