CIDR ISSUE

durairaj29

Hi
I had gone through one of the websites, from that i got this question, could someone give me the description how could we get this answer
Which two subnetworks would be included in the summarized address of 172.31.80.0 /20? (Choose two.)
A. 172.31.17.4 /30
B. 172.31.51.16 /30
C. 172.31.64.0 /18
D. 172.31.80.0 /22
E. 172.31.92.0 /22
F. 172.31.192.0 /18

Answer: DE

mikearama

durairaj29 wrote:

Which two subnetworks would be included in the summarized address of 172.31.80.0 /20? (Choose two.)
A. 172.31.17.4 /30
B. 172.31.51.16 /30
C. 172.31.64.0 /18
D. 172.31.80.0 /22
E. 172.31.92.0 /22
F. 172.31.192.0 /18

Answer: DE

The /20 provides a mask of 255.255.240.0, with the "interesting" last bit falling on the binary point equalling 16. Therefore, this summary address would include every subnet from 172.31.80, plus 16 more... ending at 172.31.96.0

Based on that range, only D and E apply.

HTH's,
Mike