Two years ago, the use of the SID Argument field was first validated with a limited set of vendor implementations. In this year’s testing, the same capability was verified across a broader multi-vendor environment. The results showed consistent support for SRv6 SID argument signaling, indicating increased maturity and adoption.

The objective of the test is to validate interoperable split-horizon loop prevention for EVPN ELAN over an SRv6 data plane. The topology used an all-active multi-homing model. BUM traffic was forwarded to the same Ethernet Segment, and split-horizon filtering was required to prevent it from looping back toward the originating CE.

In this test, we confirmed that loop prevention relied on the SRv6 SID Argument, specifically the Arg.FE2 value. The ingress PE encoded this information to identify the source Ethernet Segment of the BUM traffic. The egress PE compared the received value with the local Ethernet Segment identifier. If a match was detected, the packet was discarded and not forwarded.

According to RFC 9252, when the ESI filtering approach is used with the transposition encoding scheme, the 24-bit ESI Label field of the EVPN ESI Label Extended Community carries all or part of the Argument portion of the SRv6 SID. This allows the receiving PE to reconstruct the required SRv6 behavior without advertising the full SID in the route. In contrast, RFC 9819 specifies how the SRv6 Argument is encoded in the Prefix-SID of the EVPN Auto-Discovery per ES (Route Type 1) when the ESI filtering approach is used, but it defines only the non-transposition encoding.
In our testing, we validated both encoding approaches using EVPN Route Type 1 (Auto-Discovery per ES) with the DT2M service:
With Transposition :

• SID Structure: BL: 32 NL: 16 FL: 16 AL: 16 TL: 16 TO: 64
• SID Format: `SID = ::` (Argument not directly encoded in the SID)
• Extended Community: EVPN ESI Label = ARG
• SRv6 Argument is carried in high- order bits of 24-bits ESI Label field using transposition, allowing the receiving PE to reconstruct the full SRv6 SID behavior.
  Without Transposition:
• SID Structure: BL: 32, NL: 16, FL: 16, AL: 16, TL: 0, TO: 0
• SID Format: `SID = ::ARG::` (Argument encoded directly in the SID)
• Extended Community: EVPN ESI Label (used only as the ESI label, not for argument transposition)
• The SRv6 Argument is encoded directly in the Prefix-SID, following the non-transposition encoding defined in RFC 9819.
  We verified both scenarios: the transposition-based encoding as described in RFC 9252 and the non-transposition encoding as specified in RFC 9819.

The following participants used the ESI filtering approach with transposition:

The following participants used the ESI filtering approach without transposition: