[bess] Re: Usage of End.DX2 SID in EVPN-VPWS

["Pablo Camarillo (pcamaril)" <[e-mail]>]

Hi Sasha,

RFC 8986 specifies the fundamental data-plane pseudocode/primitive endpoint behaviors under nominal operation where the SID and outgoing interface I are active and valid.

Interface Failure and Protection: RFC 8986 intentionally does not embed protection, fast reroute (FRR), or multi-homing state machines into the base endpoint definition. Instead, interface failure handling and protection mechanisms are governed by the relevant service layer and fast-convergence specifications (such as EVPN multi-homing in RFC 9252 / BESS SRv6 EVPN and TI-LFA / Egress Protection frameworks).

Rerouting / Backup Encapsulation: In an EVPN VPWS or multi-homed active-standby/all-active scenario where interface I fails, an implementation that supports local egress protection / bypass may pre-program a backup path in the FIB. When I goes down, the node can encapsulate the decapsulated Ethernet frame into an SRv6 policy toward the backup PE's Service SID (or alternate interface) prior to control-plane reconvergence. This is an application of standard service-layer protection/FRR on top of the base behavior and is fully compliant with the architecture.

Hope this clarifies it. Let us know if you have any further questions.

Cheers,

Pablo.

From: Alexander Vainshtein <Alexander.Vainshtein=[e-mail]>
Date: Tuesday, 15 September 2026 at 03:26
To: [e-mail] <[e-mail]>
Cc: BESS <[e-mail]>
Subject: [bess] Re: Usage of End.DX2 SID in EVPN-VPWS

Hi all,
A gentle reminder: I have not received feedback from the SPRING WG on my email sent 3 months ago,

The question in this email can be re-formulated differently:

Suppose that an SID with endpoint with behavior End. DX2 has been defined and associated with the outgoing interface I.
As long as I is operationally UP, packets received with this SID as the Destination IPv6 address in the IPv6 header shall be processed as defined in the standard, i.e.:

  *   IPv6 header and all extension headers will be stripped
  *   The resulting Ethernet frame shall be sent "as is: via I
The question:
How will packets received with this SID as the Destination IPv6 address in the IPv6 header be processed if I is operationally DOWN?
Can we say that such packets MUST be discarded?


Regards, and lots of thanks in advance,
Sasha

From: Alexander Vainshtein
Sent: Thursday, June 11, 2026 7:10 PM
To: [e-mail]
Cc: BESS <[e-mail]>
Subject: Usage of End.DX2 SID in EVPN-VPWS
Importance: High

Hi,
I have a question about usage of End.DX2 SID (as defined in Section 4.9 of RFC 8986<https://datatracker.ietf.org/doc/html/rfc8986#section-4.9>in EVPN-VPWS.


*         The definition of this endpoint behavior says that "The End.DX2 SID MUST be the last segment in an SR Policy, and it is associated with one outgoing interface I"

*         If the upper-layer header type is Ethernet, the IPv6 header and all extension headers are stripped, and the resulting Ethernet frame is forwarded to the outgoing interface I.

EVPN-VPWS as defined in RFC 8214 is explicitly mentioned as one of possible applications in this section,  and Section 6.1.2 of RFC 9252<https://datatracker.ietf.org/doc/html/rfc9252#section-6.1.2> explicitly mentions End.DX2 as one of possible behaviors of the SID signaled in per-EVI Ethernet A-D routes (along with End.X2V and End.DT2U).


I think that End.X2  behavior as defined above is not compatible with one of the advantageous features of EVPN-VPWS as described in the last para of Section 5 of RFC 8214<https://datatracker.ietf.org/doc/html/rfc8214#section-5>:
<quote>
   Finally, EVPN may employ data-plane egress link protection mechanisms
   not available in VPWS.  This can be done by the primary PE (on local
   AC down) using the label advertised in the per-EVI Ethernet A-D route
   by the backup PE to encapsulate the traffic and direct it to the
   backup PE.
<end quote>

(For the reference, implementing fast egress protection against AC failure  in "classic" VPWS has been defined in RFC 8104).

What, if anything, did I miss? Do you think that a new Endpoint behavior should be defined?

Regards, and lots of thanks in advance,
Sasha




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