After the update in the previous question, the link N1-N2 goes down. N2 will reflect this change immediately in its distance vector as cost, $\infty$. After the NEXT ROUND of update, what will be the cost to N1 in the distance vector of N3?

From the previous update round:

• In the previous round, $N_3$ sent its old distance vector $(7, 6, 0, 2, 6)$ to its neighbors.

• $N_4$ sent its distance vector $(8, 7, 2, 0, 4)$ to its neighbors.

• $N_2$ sent its distance vector to $N_3$, which $N_3$ used in the previous question to become $(3, 2, 0, 2, 5)$.

Now, between rounds, the link $N_1$-$N_2$ goes down:

• $N_2$ immediately sets its cost/distance to $N_1$ to $\infty$ in its local distance vector before the new exchange, or discovers it upon failure.

• In this round of exchange:

  • $N_3$ receives the distance vectors from its neighbors $N_2$ and $N_4$.

  • $N_2$'s distance to $N_1$ is $\infty$.

  • $N_4$'s distance to $N_1$ is $8$ (from $N_4$'s vector: $(8, 7, 2, 0, 4)$).

Now node $N_3$ recomputes its distance to $N_1$:

Thus, the new cost to $N_1$ in the distance vector of $N_3$ is 10.

Therefore, option C is the correct choice.