JN0-664 Exam Dumps : Service Provider Professional (JNCIP-SP)

In the exhibit, we see two VRF (Virtual Routing and Forwarding) instances, CE-1 and CE-2, configured on a Juniper router. Each VRF is associated with a route-distinguisher (RD) and a vrf-target value.

Understanding the Role of vrf-target

The vrf-target is used to define Route Targets (RT), which control the import and export of VPN routes in MPLS Layer 3 VPNs (L3VPNs).

If two VRFs share the same RT, they will import each other's routes, allowing communication between them.

In this case, both VRFs have the same vrf-target:

vrf-target target:65512:100;

Since both CE-1 and CE-2 have the same RT (65512:100), they will import and export each other’s routes, enabling route sharing between them.

Understanding route-distinguisher (RD)

The RD (Route Distinguisher) only ensures uniqueness of overlapping IP prefixes within the MPLS network.

It does not control route sharing between VRFs.

In the exhibit, both VRFs have the same RD (65512:1), but this does not influence whether they share routes.

Correct Answer Selection

A (Correct): The vrf-target configuration enables route sharing between CE-1 and CE-2 since they have the same RT (65512:100).

B (Incorrect): The vrf-target does the opposite—it allows sharing, not blocking.

C (Incorrect): The route-distinguisher only provides unique route identification, but does not affect route sharing.

D (Incorrect): Again, route-distinguisher has no impact on route sharing.

Reference from Juniper Official Documentation

✅ Juniper Documentation - Junos MPLS VPNs Configuration Guide:

"Route targets (vrf-target) are used to control the import and export of VPN routes between different VRFs. VRFs with the same route target can import and export routes to each other, enabling inter-VRF communication."

Thus, the correct answer is:

✅ A. The vrf-target configuration will allow routes to be shared between CE-1 and CE-2.

The attached bit is a flag in an IS-IS LSP that indicates whether a router is connected to another area or level (L2) of the network. By default, L2 routers set this bit when they advertise their LSPs to L1 routers, and L1 routers use this bit to select a default route to reach other areas or levels through L2 routers. However, this may result in suboptimal routing if there are multiple L2 routers with different paths to other areas or levels. To ensure that L1 routers have only the most specific routes available from L2 routers, you can configure the ignore-attached-bit parameter on all L1 routers. This makes L1 routers ignore the attached bit and install all interarea routes learned from L2 routers in their routing tables.

The customer interface in an LDP-signaled pseudowire is the interface on the PE router that connects to the CE device. An LDP-signaled pseudowire is a type of Layer 2 circuit that uses LDP to establish a point-to-point connection between two PE routers over an MPLS network. The customer interface can have different encapsulation types depending on the type of traffic that is carried over the pseudowire. The encapsulation types are ethernet-ccc, vlan-ccc, extended-vlan-ccc, atm-ccc, frame-relay-ccc, ppp-ccc, cisco-hdlc-ccc, and tcc-ccc. Depending on the encapsulation type, the customer interface can accept or reject tagged or untagged frames in the data plane, and include or exclude VLAN tags in the control plane LDP advertisement. The following table summarizes the behavior of different encapsulation types: