Subnetting exercises 1 of 2

1. A network administrator has been provided with the following Class B block of IP addresses:
It is his task to subnet this Classful network to have (at least) 9 subnets available and maximize the number of hosts available pèr subnet.
A. What is the new netmask?
B. What are the ranges of IP addresses within each subnet?
C.What are the network and broadcast addresses within each subnet?
D.What is the number of IP addresses available for host – assignment in each subnet?



A. The netmask will have to be expanded with 4 bits so /16 → /20.
This results in a netmask of

B. All addresses start with 172.16.  ->
[0.0-15.255] [64.0-79.255] [128.0-143.255] [192.0-207.255]
[16.0-31.255] [80.0-95.255] [144.0-159.255] [208.0-223.255]
[32.0-47.255] [96.0-111.255] [160.0-175.225] [224.0-239.255]
[48.0-63.255] [112.0-127.255] [176.0-191.255] [240.0-255.255]

C.The lowest and highest addresses in each individual subnet, so eg : &, &, etc.

D. (2^h-2)=(2^12-2)=4094

E. What would be the effect on the network this design if the router in question is configured with “no ip subnet-zero”?

The lowest and highest subnetworks – and – would be rendered unusable. There would still be 16 – 2 = 14 subnetworks left, which is sufficient for the needs mentioned above, so there would be no impact on the network design.

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