Cisco ENCOR (MPLS) 3

Question 1

In MPLS VPN, what address family does the PE router use to distribute VPN routes between PEs via BGP?

Accepted Answer

VPNv4

Answer

PEs use the VPNv4 address family (RFC 4364) which prepends a Route Distinguisher to IPv4 prefixes to make them globally unique.

Question 2

What is the purpose of a Route Distinguisher (RD) in MPLS L3VPN?

Accepted Answer

Makes overlapping customer IP prefixes unique in the BGP table

Answer

The RD is prepended to customer prefixes to create unique VPNv4 routes, allowing overlapping IP space from different customers to coexist in the BGP table.

Question 3

What is the function of a Route Target (RT) in MPLS L3VPN?

Accepted Answer

Controls import and export of routes into VRFs

Answer

Route Targets are BGP extended communities used to control which routes are exported from and imported into each VRF.

Question 4

In MPLS L3VPN, how many labels are typically imposed on a packet as it enters the MPLS network?

Accepted Answer

Two labels — VPN label and transport label

Answer

Two labels are used: the inner VPN label (assigned by the egress PE to identify the VRF/CE) and the outer transport label (for forwarding across the MPLS core).

Question 5

Which command verifies the MPLS label bindings learned via LDP on a Cisco router?

Accepted Answer

show mpls ldp bindings

Answer

The 'show mpls ldp bindings' command displays the label bindings that LDP has distributed and received for each prefix.

Cisco ENCOR Practice Test

Cisco ENCOR Practice Test

Cisco ENCOR (MPLS) 3