Week 11: MPLS

Question 1

What is Multi-Protocol Label Switching (MPLS)?

Answer 1

A switching technique that directs data from one node to the next based on short path labels rather than long network addresses

Question 2

What does MPLS do?

Answer 2

Label Switching

• Reduce IP Lookup
• Speeding up network traffic flow

Question 3

What type of networking protocol is MPLS?

Answer 3

Layer 2.5

Question 4

What is MPLS called?

Answer 4

Multiprotocol

Question 5

Why is MPLS called multiprotocol?

Answer 5

because it can encapsulate packets of various network protocols like IP, ATM, SONET, and Frame Relay

Question 6

What can MPLS create?

Answer 6

End-to-End paths that act like circuit switched connections but deliver Layer 3 IP Packets

Question 7

What is a Label Switched Path (LSP)?

Answer 7

A unidirectional tunnel between a pair of routers, routed across an MPLS network

Question 8

What is a Label Edge Router (LER)?

Answer 8

The router which encapsulates a packet inside an MPLS LSP; Also the router which makes the initial path selection

Question 9

What is a Label Switching Router (LSR)?

Answer 9

A router which only does MPLS switching in the middle of an LSP

Question 10

What is a Provider Edge/Equipment (PE)?

Answer 10

LER’s that function as ingress/egress routers to the VPN

Question 11

What is a Provider Router?

Answer 11

Devices that function only as transmit routers

Question 12

What is Label Distribution Protocol?

Answer 12

Distributes labels between LER’s & LSR’s

Question 13

What is a Forward Equivalence Class (FEC)?

Answer 13

Used in MPLS to describe a set of packets with similar characteristics, which may be forwarded the same way

Question 14

An FEC correspond to what?

Answer 14

LSP

Question 15

What is Penultimate Hop Popping (PHP)?

Answer 15

A process where the outermost label of an MPLS tagged packet is removed by a LSR before the packet is passed to an adjacent LER

Question 16

What is the benefit of PHP?

Answer 16

• Reduces the load on the LER

- LER advertise a label with a value of 3 to its neighbours

Question 17

What is Independent Label Creation?

Answer 17

When routers assign MPLS labels to each of the non-directly connected IPv4 networks in the routing table

Question 18

What must be done after labels are created?

Answer 18

they must be negotiated

Question 19

What is Label Advertisement?

Answer 19

MPLS enabled routers negotiate the MPLS labels using a protocol that distribute the labels

Question 20

What is the primary protocol used in Label Advertisement?

Answer 20

Label Distribution Protocol (LDP)

Question 21

True or False: Routers need labels for directly connected networks

Answer 21

False, Routers do not need labels for directly connected networks (the same principle applies to neighbour routers)

Question 22

What does Label #3 in MPLS Label Advertisement mean?

Answer 22

Pop the MPLS header

Question 23

In MPLS Label Advertisement, in what mode do routers advertise their locally created labels?

Answer 23

Unsolicited Mode

Question 24

Under what condition will Labels be accepted in MPLS Label Advertisement?

Answer 24

If the router advertising the label is in the best path to the destination or downstream