QuestionQ5

EVPN for ELINE services

Which statement correctly describes how a single-homed EVPN VPWS operates?

  • A The same tag ID must be configured for the local attachment circuit (AC) at each PE.
  • B Each PE advertises a MAC route and an A-D per EVI route when its local AC becomes operationally UP.
  • C The advertised A-D per EVI route includes a non-zero tag ID and a non-zero MPLS label.
  • D Each PE verifies that the received tag ID matches its configured local AC tag ID.
Explanation

RFC 8214 specifies that EVPN-VPWS uses only Ethernet Auto-Discovery (A-D) per-EVI routes (Type 1) — it does not use MAC/IP Advertisement routes, since no MAC learning or lookup is required for a point-to-point VPWS service. When a PE advertises its per-EVI A-D route, the Ethernet Tag ID field must always be set to a non-zero value, representing the locally significant VPWS service instance identifier for that PE's attachment circuit, and the route also carries a non-zero MPLS label that the remote PE uses in the data plane to forward traffic to the correct egress AC. The two PEs' local AC tag/VLAN values do not need to match each other; EVPN-VPWS does not require tag translation or verification between PEs — the MPLS label, not the tag value, identifies the destination AC.

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