Question

b) Give brief information about NSFNET that form the backbone of the Internet in early 1990s? How many routers were involved?

c) Consider a router that interconnects three subnets: Subnet 1, Subnet 2, and Subnet 3. Suppose all of the interfaces in each of these three subnets are required to have the prefix 223.1.17/24. Also suppose that Subnet 1 is required to support up to 63 interfaces, Subnet 2 is to support up to 95 interfaces, and Subnet 3 is to support up to 16 interfaces. Provide three network addresses (of the form a.b.c.d/x) that satisfy these constraints.

Answer 1

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Ans.b) Give brief information about NSFNET that form the backbone of the Internet in early 1990s? How many routers were involved?

• NSFNET (National Science Foundation Network) was the program which was funded to coordinate and promote the education and advanced research in the networking in the United States. This NSFET worked as a hub for the five university based computer centres and helped sharing the data. This worked between the 1985-1995 and is considered to form the backbone of the internet in the early 1990's.
• Total 1 router was been there in use as the 5 universities were connected in a WAN of the NSFET therefore the required routers was 1 as the connections were direct.

Ans.c) Note: The question needs a minor correction otherwise it is not possible to create 3 subnets with these number of interfaces the subnet 1 will require 62 interface in place of 63. Now we will proceed

The three network addresses would be as follows:

• 223.1.17.0/25 - Subnet 2
• 223.1.17.128/25 - Subnet 1
• 223.1.17.190/26 - Subnet 3

Firstly the main IP is divided into 2 subnets for the 93 interfaces to be covered as the hosts in this would be 128, then the other subnet is divided into 2 sub-subnets for the allotment of 62 and 16 interfaces as both sub-subnets could have 62 hosts per subnet.

Formulas used = 2ⁿ - 2= total hosts per subnet and 2ⁿ = no of subnets

This is the way the subnets would be divided into three network addresses.

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