CCNP MPLS and VPN Technologies

Question 1

What is the primary function of a Label Edge Router (LER) in an MPLS network?

Accepted Answer

Push or pop MPLS labels at the boundary of the MPLS domain

Answer

An LER (also called PE router) sits at the edge of the MPLS domain and is responsible for pushing labels onto incoming IP packets or popping labels from outgoing packets.

Question 2

In MPLS LDP, what is the default label distribution mode on Cisco routers?

Accepted Answer

Independent control with downstream unsolicited

Answer

Cisco IOS uses independent control mode with downstream unsolicited distribution by default, meaning each LSR independently assigns and advertises labels without waiting for downstream peers.

Question 3

Which MPLS label value is reserved to indicate the Explicit Null label for IPv4?

Accepted Answer

0

Answer

Label value 0 is the IPv4 Explicit Null label, which signals that the label must be popped but the packet should still be forwarded based on its IP header.

Question 4

What mechanism does Penultimate Hop Popping (PHP) use to reduce processing on the egress LSR?

Accepted Answer

The second-to-last LSR pops the outermost label before the final hop

Answer

PHP allows the penultimate (second-to-last) LSR to remove the top MPLS label so the egress LSR receives a plain IP packet or inner label, reducing its lookup overhead.

Question 5

In an MPLS L3VPN, which protocol is used to exchange VPN routing information between PE routers?

Accepted Answer

MP-BGP with VPNv4 address family

Answer

Multiprotocol BGP (MP-BGP) with the VPNv4 address family carries customer VPN prefixes between PE routers using Route Distinguishers and Route Targets to separate and import/export routes.

CCNP - Cisco Certified Network Professional Practice Test

CCNP - Cisco Certified Network Professional Practice Test

CCNP MPLS and VPN Technologies