Subnetting question from cisco practice test

Abrown1966

I am using Cisco's CCNA study guide and am taking the practice test supplied with the books.

One of the questions includes the following subnets which i beleive overlap. Someone please correct me if I am wrong.

The subnets used in the question a re a s follows:

Subnet # subnet/prefix ip address range
1 172.30.0.0/22 172.30.0.0 to 172.30.3.255
2 172.30.4.28/30 172.30.4.28 to 172.30.4.31
3 172.30.4.56/30 172.30.4.56 to 172.30.4.59
4 172.30.6.0/24 172.30.6.0 to 172.30.6.255
5 172.30.7.0/23 172.30.6.0 to 172.30.7.255
6 172.30.8.0/21 172.30.8.0 to 172.30.15.255

Do the addressess in subnet 4 and 5 overlap?

phantasm

Did you try writing it out in binary?

karanc

they are not over lapping

for 4th ip range is 172.30.6.1 - 172.30.6.254
for 5th ip range is 172.30.7.1 - 172.30.7.254

so i dont c any overlapping

dynamik

Maybe I'm confused, but I don't think you can have 7 in the third octet if it's /23.

172.30.7.0 is 10101100.00011110.0000111.00000000, but you need to borrow that last bit in the third octet in order to use /23.

Did you check the errata? Maybe it was supposed to be /24

vjsousa

I agree with dynamik. Maybe it was supposed to be /24. Because you cant have 7 in the third octet is it is /23. For a /24 you could have 172.30.7.0/24 > 172.30.7.1 - 172.30.7.254, broadcast 172.30.7.255.