Free Cisco ENCOR (MPLS) Question and Answers

Question 1

What Cisco-exclusive technology is MPLS based on?

Accepted Answer

CEF

Answer

MPLS (Multiprotocol Label Switching) is built upon Cisco Express Forwarding (CEF) for its high-speed packet forwarding capabilities. CEF pre-computes the entire forwarding path for IP packets, creating a Forwarding Information Base (FIB) and adjacency table. MPLS leverages these pre-computed paths, replacing slower IP lookups with efficient label lookups for faster data plane operations.

Question 2

What table does CEF create?

Accepted Answer

FIB

Answer

Cisco Express Forwarding (CEF) is a high-performance, distributed switching mechanism that creates the Forwarding Information Base (FIB) table. The FIB is a database containing pre-computed next-hop information for all known routes, enabling routers to make rapid and efficient IP packet forwarding decisions without needing to consult the routing table for every packet.

Question 3

What ISP router, for example, adds labels to routes discovered by BGP?

Accepted Answer

LSR Label Switching Router

Answer

A Label Switching Router (LSR) is a core component in an MPLS network responsible for forwarding packets based on labels. Specifically, an Ingress LSR (the edge router where traffic enters the MPLS domain) will add (push) labels to IP packets based on routing information, such as routes discovered by BGP, before forwarding them into the MPLS cloud.

Question 4

What are the MPLS terms for adding and removing labels?

Accepted Answer

Push and pop

Answer

In MPLS, the terms 'push' and 'pop' describe the fundamental actions of adding and removing labels from packets. 'Push' refers to the process of adding a label to an IP packet as it enters the MPLS domain, typically performed by an ingress Label Edge Router. 'Pop' refers to the removal of a label from a packet, usually done by an egress LER or the penultimate hop router before the packet leaves the MPLS domain.

Question 5

Which MPLS plane contains label 3 routing and label exchange protocols?

Accepted Answer

Control plane

Answer

The control plane in MPLS is responsible for establishing and maintaining the label forwarding information. This includes running routing protocols (like OSPF, EIGRP, BGP) to learn network topology and IP routes, as well as label distribution protocols (like LDP or RSVP-TE) to exchange label mappings among Label Switching Routers (LSRs).

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Free Cisco ENCOR (MPLS) Question and Answers