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 uses IS-IS as the control plane while L3VPN uses OSPF

Answer

VPLS requires dedicated physical links between PE routers

Answer

VPLS supports only point-to-point connections, unlike L3VPN's any-to-any model

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 backup set of labels used when the primary LSP fails

Answer

A hardware TCAM structure storing label-to-interface mappings

Answer

A Cisco IOS data structure for storing LDP peer session states

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

FRR eliminates the need for RSVP-TE signaling on the backup path

Answer

FRR uses BFD to detect failures 10x faster than RSVP keep-alives

Answer

FRR distributes traffic across all available paths simultaneously to prevent congestion

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 A (back-to-back VRF)

Answer

Option B (labeled VPNv4 between ASBRs)

Answer

Option D (GRE tunneling between PE routers)

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

It assigns an MPLS label to the IP address configured on the interface

Answer

It sets the interface as a TE tunnel endpoint for RSVP signaling

Answer

It activates MPLS QoS DiffServ mode on the interface

Question 6

In MPLS LDP, what is the significance of the LDP Router ID?

Accepted Answer

It uniquely identifies an LSR and is used as the transport address in LDP Hello messages

Answer

It determines the LDP label range allocated to each LSR in the domain

Answer

It sets the administrative distance for LDP-learned label bindings

Answer

It defines which interfaces participate in LDP discovery

Question 7

What is the function of the TTL field in an MPLS label and how does 'no mpls ip propagate-ttl' affect traceroute behavior?

Accepted Answer

The MPLS TTL prevents routing loops; disabling propagation hides LSP hops from traceroute output

Answer

The MPLS TTL enables QoS prioritization; disabling propagation forces uniform hop counts

Answer

The MPLS TTL carries DSCP values; disabling propagation strips QoS markings at the PE

Answer

The MPLS TTL signals PHP; disabling propagation forces explicit null on all interfaces