Auto-derived Route Targets

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 that are not present on all PE devices. Without the auto-derived target option enabled, EVPN Type 2 and Type 3 routes are imported into the EVPN instances (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.

Understanding Auto-Derived Route Targets

Route targets identify the different routes that are imported and exported into the VRF tables. When you enable the auto-derived route targets option, the device 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).

Devices don't auto-derive the route targets for EVPN route types other than Type 2 and Type 3. As a result, in some cases you must manually configure route targets in routing instances for EVPN route types such as:

• EVPN Type 1 routes: Devices use these routes to reach all the multihomed devices associated with a ESI. You configure route targets for this type of route manually in the EVPN instance.

• EVPN Type 5 routes: Devices use these routes to advertise IP prefixes assigned within a data center to devices in other data centers, enabling communication across data centers. You configure route targets for this type of route manually in Type 5 virtual routing and forwarding (VRF) instances.

See Example: Configuring VNI Route Targets Manually and Example: Configuring VNI Route Targets Automatically with Manual Override for more on configuring route targets manually at the global level (applicable to all EVPN route types) or manually at the virtual network identifier (VNI) level (applicable to EVPN Type 2 and Type 3 routes).

Devices automatically derive route targets for EVPN Type 2 and Type 3 routes based on the following parameters:

• For EVPN-MPLS: From the VLAN ID (VID).

• For EVPN-VXLAN: From the VXLAN network identifier (VNI).

• For PBB-EVPN: From the instance service identifier (ISID).

For EVPN Type 2 and Type 3 routes, the auto-derived route targets have higher precedence over route targets you configure manually at the global level in vrf-target statements, vrf-export policies, and vrf-import policies.

As defined in RFC8365, the auto-derived route target field includes the following fields:

• Global Administrator—A 2-octet field containing an autonomous system (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:

We don't support auto-derived route targets for inter-AS routing.

To enable auto-derived route targets, include the auto statement at the [edit routing-instances routing-instance-name vrf-target]. We support configuring auto-derived route targets with these L2 instance types:

• The default switch instance at the [edit switch-options] hierarchy level.

• Virtual switch instances using instance-type virtual-switch at the [edit routing-instances virtual-switch-instance-name] hierarchy level.

• EVPN instances using:

  • instance-type evpn at the [edit routing-instances evpn-instance-name] hierarchy level.

  • instance-type mac-vrf at the [edit routing-instances mac-vrf-instance-name] hierarchy level.

The following is a sample configuration for auto-derived route targets for an EVPN instance and a virtual switch routing instance. We also manually configure a route target here in either type of EVPN instance at the global level to support EVPN Type 1 routes. The auto-derived route target applies to EVPN Type 2 and Type 3 routes, and for those route types, takes precedence over the manually defined route target at the global level.