CCNP MPLS and VPN Technologies 3

Question 1

What distinguishes VPLS (Virtual Private LAN Service) from MPLS L3VPN?

Accepted Answer

VPLS provides Layer 2 Ethernet bridging across the MPLS core, while L3VPN routes at Layer 3

Answer

VPLS emulates a multi-point Ethernet LAN across an MPLS backbone, forwarding frames based on MAC addresses in a virtual bridge domain, whereas L3VPN performs IP routing at the PE.

Question 2

In MPLS, what is a 'label stack' and when is it used?

Accepted Answer

Multiple MPLS labels stacked between the Layer 2 and Layer 3 headers, used in VPN and TE scenarios

Answer

A label stack consists of two or more MPLS labels inserted between Layer 2 and IP headers; in L3VPN, the outer label is the transport label (to the egress PE) and the inner label is the VPN label identifying the VRF.

Question 3

What is the primary advantage of MPLS Fast Reroute (FRR) over traditional IP routing convergence?

Accepted Answer

FRR pre-establishes backup LSPs so traffic is rerouted in under 50ms upon link or node failure

Answer

MPLS FRR pre-signals a bypass or detour LSP before any failure occurs, allowing the PLR (Point of Local Repair) to switch traffic to the backup path in sub-50ms when a failure is detected.

Question 4

Which MPLS inter-AS VPN option requires an MP-iBGP session between RRs in different ASes and passes VPNv4 routes end-to-end?

Accepted Answer

Option C (multi-hop eBGP between PEs across ASes)

Answer

Option C uses multi-hop eBGP to carry VPNv4 routes directly between PE routers in different ASes, with labeled IPv4 routes exchanged between ASBRs to provide transport label reachability.

Question 5

What is the purpose of the 'mpls ip' command on a Cisco router interface?

Accepted Answer

It enables LDP on the interface so it can exchange labels with directly connected LSR neighbors

Answer

The 'mpls ip' interface command enables LDP (Label Distribution Protocol) on that interface, allowing the router to discover LDP neighbors and exchange label bindings for IP prefixes.

CCNP - Cisco Certified Network Professional Practice Test

CCNP - Cisco Certified Network Professional Practice Test

CCNP MPLS and VPN Technologies 3