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#
Authors:
James F. Kurose, Keith W. Ross
Chapter:
The Link Layer: Links,access Networks, And Lans
Exercise:
Problems
Question:29 | ISBN:9780132856201 | Edition: 6

Question

Consider the MPLS network shown in Figure 5.29, and suppose that routers R5 and R6 are now MPLS enabled. Suppose that we want to perform traffic engineering so that packets from R6 destined for A are switched to A via R6- 4-R3-R1, and packets from R5 destined for A are switched via R5-R4-R2-R1. Show the MPLS tables in R5 and R6, as well as the modified table in R4, that would make this possible.

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Answer

Multiprotocol Label Switching (MPLS):

MPLS is a switching technique which is uses the fixed length label to improve the forwarding speed of the IP routers. This is also useful in virtual circuit networks.

Consider the MPLS network given in the figure 5.29 given in the textbook. Also assume that the routers R5 and R6 are MPLS enabled.

MPLS table at router R6:

The packets from router R6 that are destined to A are switched to A using the route R6-R4-R3-R1. R6 doesn’t have anything in the label. The interface 0 is used to forward the frame. The label used for outgoing interface is 7.

In label

Out label

dest

Out Interface

 

7

A

0

MPLS table at router R5:

The path R5-R4-R2-R1 is used by the router R5 to transfer the packets that are destined to A. R5 doesn’t have anything in the label. The interface 0 is used to forward the frame. The label used for outgoing interface is 5.

In label

Out label

dest

Out Interface

 

5

A

0

 

MPLS table at router R4:

The packets from the routers R5 and R6 are forwarded to A by the router R4. Using out label values, the router R4 updates it’s MPLS table.

The router R6 out label is used as in label for R4 to forward the frame from router R6 to destination A. Similarly, the router R5 out label is used as in label for R4 to forward the frame from router R5 to destination A.

In label

Out label

dest

Out Interface

7

10

A

0

 

12

D

0

5

8

A

1

 

0 0

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