Question $4$

$($a$)$ Apply Dijkstra$$s algorithm to compute the shortest path from router R$1$ to each other

router in the network shown in Figure $4\mathrm{.}1.$ The number on each line shows the cost of the

line. Based upon these calculations write down the shortest routes from R$1$ to each other

router, the route cost values, and the first$-$hop router. Your answer should be given in form

of the routing table which will show the path to each router and the corresponding cost.

Figure $4\mathrm{.}1$

$($b$)$ Give an overview of the most important improvements of the IPv$6$ protocol compared with

IPv$4.$ Is IPv$6$ compatible with IPv$4?$

$($c$)$ IPv$6$ uses two different modes of packet encryption $$ the Transport Mode and the

Tunneling Mode. Explain how these modes operate. In which part of IPv$6$ are these

features implemented?

$($d$)$ DNS transfers all messages using UDP packets. It is known that UDP packets have a

maximum length, which potentially can be as low as $576$ bytes. What do you think will

happen when a DNS name to be resolved exceeds this length? Is this possible in principle?

If no$,$ explain why. If yes, can the DNS message be sent in two $($or more$)$ packets?