Question $3$: Suppose a $4000$ bytes TCP message $($including the TCP header$)$ is passed to IP for delivery across two networks of the Internet. The first network has an MTU of $1500$ bytes; the second has an MTU of $512$ bytes. Each network$$s MTU gives the size of the largest IP datagram that can be carried in a link$-$layer frame.

$($a$)$ Give the sizes, offsets, values of offset fields in the IP headers of the sequence of

fragments delivered to the network layer at the destination host. Assume all IP headers

are $20$ bytes. Note, the IP requires that fragmentation should always happen on $8-$byte

boundaries.

$($b$)$ Path MTU is the smallest MTU of any link on the current path $($route$)$ between two hosts.

Assume that we could discover the path MTU of the path used, and that we use this value as the MTU for all the path segments. Give the sizes of the sequence of IP packets delivered to the network layer at the destination host.

Question $4.$ IP addresses. Company X and Company Y both connect to the same ISP.

Company X is assigned the prefix $121\mathrm{.}77\mathrm{.}0\mathrm{.}0/18$ and Company Y is assigned the prefix

$121\mathrm{.}77\mathrm{.}64\mathrm{.}0/18.$ The ISP has a single $3-$port router: port $1$ connects to Company X$,$ port $2$

connects to Company Y$,$ and port $3$ connects to the rest of the Internet.

a$)$ Draw and complete $($as best you can$)$ the contents of the forwarding table in the ISP$$s router.

b$)$ What aggregated prefix does the router advertize to the rest of the Internet so that packets can reach both Company X and Company Y$?$ Question $6$: The following table is a routing table using CIDR. Address bytes are in

hexadecimal.

Net$/$MaskLength Next hop

C$4\mathrm{.}50\mathrm{.}00\mathrm{.}00/12$ A

C$4\mathrm{.}5$E$\mathrm{.}10\mathrm{.}00/20$ B

C$4\mathrm{.}60\mathrm{.}00\mathrm{.}00/12$ C

C$4\mathrm{.}68\mathrm{.}00\mathrm{.}00/14$ D

$80\mathrm{.}00\mathrm{.}00\mathrm{.}00/1$ E

$40\mathrm{.}00\mathrm{.}00\mathrm{.}00/2$ F

$00\mathrm{.}00\mathrm{.}00\mathrm{.}00/2$ G

State to what next hop the following will be delivered.

$($a$)$ C$4\mathrm{.}5$E$\mathrm{.}1$A$\mathrm{.}87$

$($b$)$ C$4\mathrm{.}5$E$\mathrm{.}32\mathrm{.}09$

$($c$)$ C$4\mathrm{.}69\mathrm{.}22\mathrm{.}89$

$($d$)2$E$\mathrm{.}43\mathrm{.}91\mathrm{.}12$

$($e$)9$A$\mathrm{.}88\mathrm{.}77\mathrm{.}66$

$($f$)$ C$4\mathrm{.}62\mathrm{.}31\mathrm{.}2$E

$($g$)$ C$4\mathrm{.}6$A$\mathrm{.}31\mathrm{.}2$E

Question $7.$ An organization has a class C network $212\mathrm{.}192\mathrm{.}88\mathrm{.}0$ and wants to form subnets for six departments, which host as follows:

A$.45$ hosts

B$.20$ hosts

C$.55$ hosts

D$.25$ hosts

E$.10$ hosts

F$.22$ hosts

G$.9$ hosts

There are $180$ hosts in all. Design a possible arrangement of subnets to make each department in a different subnet. For each subnet, give subnet number, subnet mask and range of IP addresses.