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6. Ethernet Tag ID

6. Ethernet Tag ID​

An Ethernet Tag ID is a 32-bit field containing either a 12-bit or 24-bit identifier that identifies a particular broadcast domain (e.g., a VLAN) in an EVPN instance. The 12-bit identifier is called the VLAN ID (VID). An EVPN instance consists of one or more broadcast domains (one or more VLANs). VLANs are assigned to a given EVPN instance by the provider of the EVPN service. A given VLAN can itself be represented by multiple VIDs. In such cases, the PEs participating in that VLAN for a given EVPN instance are responsible for performing VLAN ID translation to/from locally attached CE devices.

If a VLAN is represented by a single VID across all PE devices participating in that VLAN for that EVPN instance, then there is no need for VID translation at the PEs. Furthermore, some deployment scenarios guarantee uniqueness of VIDs across all EVPN instances; all points of attachment for a given EVPN instance use the same VID, and no other EVPN instances use that VID. This allows the RT(s) for each EVPN instance to be derived automatically from the corresponding VID, as described in Section 7.10.1.

The following subsections discuss the relationship between broadcast domains (e.g., VLANs), Ethernet Tag IDs (e.g., VIDs), and MAC-VRFs as well as the setting of the Ethernet Tag ID, in the various EVPN BGP routes (defined in Section 8), for the different types of service interfaces described in [RFC7209].

The following Ethernet Tag ID value is reserved:

  • Ethernet Tag ID {0xFFFFFFFF} is known as MAX-ET.
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