The vrf-target is a BGP extended community attribute that controls the import and export policies for routes within a VRF. In the provided configuration, both vrf-a and vrf-b share the same vrf-target value of target:100:1. When a single target is configured this way, it is used for both import and export policies. Consequently, routes learned from CE-1 in vrf-a are exported with target:100:1, and vrf-b is configured to import routes with this same target. This reciprocal relationship allows routes to be shared between the two VRFs, enabling communication between CE-1 and CE-2.

B. A shared vrf-target is the mechanism that enables route sharing between VRFs, it does not prevent it.

C. The route-distinguisher's function is to make IPv4 prefixes globally unique within the BGP table, not to control route sharing policy.

D. The route-distinguisher ensures route uniqueness for overlapping address spaces but does not influence the route sharing policy between VRFs.

1. Juniper Networks TechLibrary

Junos OS VPNs Library for Routing Devices

"Configuring Routing Instances on PE Routers in VPNs": This document explains that the vrf-target statement specifies the route target extended community. When a single target: is configured

it is used for both import and export policies

controlling which routes are accepted into and advertised from the VRF. The shared target target:100:1 in the exhibit explicitly creates a policy for route exchange between the two VRFs.

2. Juniper Networks TechLibrary

Junos OS VPNs Library for Routing Devices

"Route Distinguishers in VPNs Overview": This source clarifies the role of the route distinguisher (RD). It states

"The main purpose of the route distinguisher is to create unique VPN-IPv4 addresses for use in the service provider’s network." This confirms that the RD's function is to ensure uniqueness

not to control route distribution policy

which is the role of the route target.

3. Juniper Networks TechLibrary

Junos OS VPNs Library for Routing Devices

"Understanding VRF Import and Export Policies in L3VPNs": This document details how route targets function. It specifies that for a route to be accepted into a VRF's routing table (e.g.

vrf-b.inet.0)

the route must have a route target community that matches one of the communities listed in the vrf-import policy of that VRF. The configuration in the exhibit establishes this matching condition between vrf-a and vrf-b.