Question $3)$

a$)$ An Internet Service Provider $($ISP$)$ has bought the right to use the IP addresses in the range

from $213\mathrm{.}49\mathrm{.}0\mathrm{.}0$ to $214\mathrm{.}57\mathrm{.}255\mathrm{.}255.$ It uses Classless Inter$-$Domain Routing $($CIDR$)$ to route

traffic to these addresses. It receives a number of requests from companies. First

company A buys a block of $12,500$ addresses, then company B requests $4,500,$ followed

by company C with $700$ addresses and company D requests $300$ addresses. The ISP

processes these requests in the order it receives them.

i$)$ What is the address range allocated for each client? Give the first and last address of

the range, the number of significant bits and the subnet mask.

ii$)$ If CIDR wasn't used, what classes of network addresses would be allocated to each

client? How many addresses would be allocated in total? What would be the fraction

of addresses actually used by each client? Compare this to the use of CIDR.

iii$)$ Describe a structured approach to the allocation of IP addresses that the ISP could

employ in comparison to allocating IP addresses from the available address range as

request arrive.

$[25$ marks$]$

b$)$ Distance Vector Routing represents a fundamental approach to routing that is

implemented in routing protocols such as the Routing Information Protocol $($RIP$).$

i$)$ Explain the process of establishing a routing table using Distance Vector Routing for

node $A$ of the topology shown in figure $2.$

ii$)$ Assume that the routers in figure $2$ are replaced by OpenFlow switches and that the

network will be controlled by a central OpenFlow controller. Describe the information

that needs to be kept at the controller and the switches and the messages that may

need to be exchanged between the controller and the switches in order for packets to

be transferred from node $A$ to node $L.$

Figure $2$: Topology of interconnected routers