Question
Consider again the same scenario as in the previous problem, but suppose that packets from R6 destined for D are switched via R6-R4-R3, while packets fromR5 destined to D are switched via R4-R2-R1-R3. Show the MPLS tables in all routers that would make this possible.
Answer
Multiprotocol Label Switching (MPLS):
- The 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.
The following MPLS tables in all routers(R5-R4-R2-R1-R3) as:
Consider again the same scenario as in the previous problem (29P) and 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 ‘D’ are switched to path using the route R6-R4-R3.
- The route R6 doesn’t have anything in the label. The label used for outgoing interface is 3.
|
In Label |
Out Label |
Dest(Destination) |
Out Interface |
|
|
3 |
D |
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'
- The R5 doesn’t have anything in the label. The interface 5is used to forward the frame.
- The label used for outgoing interface is 0.
|
In Label |
Out Label |
Dest(Destination) |
Out Interface |
|
|
5 |
A |
0 |
MPLS table at router R4:
- The packets from the routers R5 and R6 are forwarded to destination ‘D’ 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 ‘D’.
- Same as, the router R5 out label is used as in label for R4 to forward the frame from router R5 to destination ‘D’.
|
In Label |
Out Label |
Dest(Destination) |
Out Interface |
|
3 2
|
12 4
|
D D
|
0 1 |
MPLS table at router R2:
- The path R4-R2-R1-R3 is used by the router R4 to transfer the packets that are destined to ‘D’.
- The R4 doesn’t have anything in the label.
- The interface 1 is used to forward the frame. The label used for outgoing interface is 0.
|
In Label |
Out Label |
Dest(Destination) |
Out Interface |
|
4 |
1 |
D |
0 |
MPLS table at router R1:
- The packets from router R6 that are destined to 'D' are switched to A using the route R4-R2-R1-R3.
- The router R2 doesn’t have anything in the label.
- The interface 12 is used to forward the frame. The label used for outgoing interface is 1.
|
In Label |
Out Label |
Dest(Destination) |
Out Interface |
|
1 |
12 |
D |
1 |
MPLS table at router R3:
- The packets from the router forwards R3 that are destined to ‘D’. The router R4 shows the next packet as R3 from the router R6 with the In label as 12.
- The router R1 reaches the router R3 with the out interface as 0.
|
In Label |
Out Label |
Dest(Destination) |
Out Interface |
|
12 |
.......... |
D |
0 |