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.
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:
routing-instances {
VS-1 {
instance-type virtual-switch;
interface ae0.110;
interface ae1.120;
interface ae2.130;
route-distinguisher 100.100.100.2:101;
vrf-target {
target:100:101;
auto;
}
protocols {
evpn {
extended-vlan-list [ 110 120 130 ];
}
}
bridge-domains {
bd-110 {
vlan-id 110;
}
bd-120 {
vlan-id 120;
}
bd-130 {
vlan-id 130;
}
}
}
EVPN-1 {
instance-type evpn;
vlan-id 10;
interface ae0.0;
interface ae1.0;
interface ae2.0;
route-distinguisher 100.100.100.2:1;
vrf-target {
target:100:1
auto;
}
protocols {
evpn;
}
}
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.