help me with this one

Hi,
I came across this question.
Which of the following is a summarization address for the networks 172.21.136.0/24 and 172.21.143.0/24?
A.172.21.136.0/21
B.172.21.136.0/20
C.172.21.136.0/22
D. 172.21.128.0/2

I don't know the correct answer , and to be frank enough I don't understand this question.

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Comments

rc240sx

Well this is how I look at the question. How many addresses between them. Between 36 and 43 there are 6 addresses so you need six bits. C is the answer because /22 is borrowing six bits. Im not 100% sure though.

jontebond

im sure its A
lets see you suggested 6 bits, well then 22 is not enough:

from
255.255.255.0 / 24
11111111.11111111.11111111.00000000
255.255.252.0 /22
11111111.11111111.11111100.00000000
then we have 3 bits remember binary counting:
128 64 32 16 8 4 2 1

172.21.136.0 - 172.21.143.0 7 bitar
255.255.248.0 / 21
11111111.11111111.11111000.00000000

supernetting complete:
172.21.136.0 --> 172.21.143.0
correct answer A:

hop this helped good luck /jonas

seth223uk

i was under the impression that supernetting was reserved for the new CCNA exam. Is this in the 607 exam objectives? It was covered briefly under extra credit in the cisco press book by wendell odom?

does anyone know? If so does anyone know any good places with tutorials on how to do this?

heres a place for you very gud revision material

http://www.cictech.co.uk/html/ccna_-_page_1.html

happi studyin