Andrew S. Tanenbaum Edition 5th Exercise 5 Question 31 (Page No. 492)

Question

A router has just received the following new IP addresses: 57.6.96.0/21,
57.6.104.0/21, 57.6.112.0/21, and 57.6.120.0/21. If all of them use the same outgoing
line, can they be aggregated? If so, to what? If not, why not?

Answer 1

Yes they can be aggregated.

$57.6.96.0/21 = 57.6.01100000.0$

$57.6.104.0/21=57.6.01101000.0$

$57.6.112.0/21=57.6.01110000.0$

$57.6.120.0/21=57.6.01111000.0$

We can see that $57.6.011$ part is common in all the IP addresses.

Thus we can do a supernetting here and keep a supernet address as :-

$57.6.96.0/19$