Virtual circuits¶
- In a network that uses virtual circuits, the forwarding paths depend on the label tables installed inside each network node.
In this network, only one of the affirmations about the forwarding paths is correct. Which one ?
To reach B, A must send packets with label=3 and the path is R1->R3
To reach A, B must send packets with label=1 and the path is R3->R2->R1
- The forwarding paths used in a virtual circuits network depend on the label forwarding tables installed in the network nodes. Sometimes, these tables must be configured manually.
In this network, which of the label forwarding tables below ensures that A and B can exchange packets in both directions.
To reach B, A sends packet with label=3. To reach A, B sends packets with label=2. New label forwarding table for R2:
InLabel | OutPort | OutLabel |
---|---|---|
2 | S | 1 |
1 | W | 1 |
The label forwarding table for R3 remains empty.
To reach B, A sends packet with label=3. To reach A, B sends packets with label=3. New label forwarding table for R2:
InLabel | OutPort | OutLabel |
---|---|---|
2 | S-W | 4 |
New label forwarding table for R3:
InLabel | OutPort | OutLabel |
---|---|---|
4 | E | 1 |
3 | N | 1 |
To reach B, A sends packet with label=2. To reach A, B sends packets with label=1. New label forwarding table for R2:
InLabel | OutPort | OutLabel |
---|---|---|
2 | S | 1 |
1 | W | 1 |
New label forwarding table for R3:
InLabel | OutPort | OutLabel |
---|---|---|
2 | E | 1 |
1 | N | 1 |
To reach B, A sends packet with label=3. To reach A, B sends packets with label=2. New label forwarding table for R2:
InLabel | OutPort | OutLabel |
---|---|---|
2 | S-W | 4 |
1 | S-W | 2 |
New label forwarding table for R3:
InLabel | OutPort | OutLabel |
---|---|---|
4 | E | 1 |
2 | E | 2 |
- The forwarding paths used in a virtual circuits network depend on the label forwarding tables installed in the network nodes. Sometimes, these tables must be configured manually.
In this network, which of the label forwarding tables below ensures that : both A and B can exchange packets in both directions and that the path from A to B is the reverse of the path from B to A
To reach B, A sends packets with label=2. To reach A, B sends packets with label=3. New label forwarding table for R3:
InLabel | OutPort | OutLabel |
---|---|---|
2 | E | 1 |
6 | N | 1 |
New label forwarding table for R2:
InLabel | OutPort | OutLabel |
---|---|---|
3 | S-W | 2 |
5 | W | 2 |
To reach B, A sends packets with label=3. To reach A, B sends packets with label=2. New label forwarding table for R2:
InLabel | OutPort | OutLabel |
---|---|---|
5 | W | 1 |
3 | S | 1 |
New label forwarding table for R3:
InLabel | OutPort | OutLabel |
---|---|---|
3 | N-W | 2 |
5 | N | 2 |
To reach B, A sends packets with label=2. To reach A, B sends packets with label=2. New label forwarding table for R2:
InLabel | OutPort | OutLabel |
---|---|---|
5 | W | 1 |
6 | S | 1 |
New label forwarding table for R3:
InLabel | OutPort | OutLabel |
---|---|---|
2 | E | 1 |
5 | N | 2 |
To reach B, A sends packets with label=3. To reach A, B sends packets with label=3. New label forwarding table for R2:
InLabel | OutPort | OutLabel |
---|---|---|
5 | W | 1 |
3 | S | 1 |
New label forwarding table for R3:
InLabel | OutPort | OutLabel |
---|---|---|
6 | N-W | 5 |
5 | N | 2 |
To reach B, A sends packets with label=2. To reach A, B sends packets with label=3. New label forwarding table for R2:
InLabel | OutPort | OutLabel |
---|---|---|
2 | S | 1 |
1 | W | 1 |
New label forwarding table for R3:
InLabel | OutPort | OutLabel |
---|---|---|
6 | N | 1 |
1 | E | 1 |