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Auto-derived Route targets

 

Route targets are used to identify the different routes that are imported and exported into the VRF tables. When you enable the auto-derived route targets option , Junos derives the route targets based on the EVPN encapsulation for EVPN route type 2 (MAC/IP Advertisement Route) and EVPN route type 3 (Inclusive Multicast Ethernet Tag route). The route targets for remaining EVPN route types are not auto-derived. For EVPN-MPLS, the route target is automatically derived from the VLAN ID (VID). For EVPN-VXLAN, the route target is automatically derived from the VXLAN network identifier (VNI). For PBB-EVPN, the route target is derived from instance service identifier (ISID). The auto-derived route targets have higher precedence over manually configured route targets in vrf-targets, vrf-export policies, and vrf-import policies.

As defined in RFC 8365, the auto-derived route target field includes the following fields:

  • Global Administrator—A 2-octet field containing an AS number assigned by Internet Assigned Numbers Authority (IANA).

  • Local Adminstrator—A 4-Octet field that includes the following:

    • A single bit field with a value of zero indicating that the RT is auto-derived.

    • Type—A 3-bit field identifying the service.

    • D-ID—A 4-bit field identifying the domain ID.

    • Service ID—A 3-octet field set to the VNI, VSID, I-SID, or VID.

Note

Auto-derived route targets are not supported for inter-AS routing.

To enable auto-derived route targets, include the auto statement at the [edit routing-instances routing-instance-name vrf-target]. Auto-derived route targets are supported on virtual switch and EVPN routing instances.

The following is a sample configuration for auto-derived route targets for an EVPN and virtual switch routing instance:

Benefits of Auto-Derived Route Targets

Auto-derived route targets simplify the configuration of VLAN services for EVPN, especially in VLAN-aware bundle services where you can have multiple VLANs, multiple bridge domains and the VLANS for a given service are not present on all PE devices. Without auto-derived target option enabled, EVPN type 2 and type 3 routes are imported into the EVIs on all receiving PE devices and the routes subsequently dropped for non-existing VLANs (bridge-domains). To minimize the number of routes that are distributed, different auto-derived route targets can be used within each bridge-domain. Together with constrained route distribution as described in RFC 4684, you can limit the distribution of bridge-domain specific EVPN route types (Type 2 and Type 3) to only the interested PE devices.