Help understanding this question

hellopaul2000mail

Hi all, just come accross a subnetting question i dont understand, any chance someone could explane it to me

cheers

Select all that apply. Which of the following /24 subnets can be supernetted into a larger network?

a)10.10.20.0 /24 and 10.10.21.0 /24 into 10.10.20.0 /23

b)10.10.21.0 /24 and 10.10.22.0 /24 into 10.10.21.0 /23

c)10.10.130.0 /24, 10.10.131.0 /24, 10.10.132.0 /24, and 10.10.133.0 /24 into 10.10.130.0 /22

d)10.10.164.0 /24, 10.10.165.0 /24, 10.10.166.0 /24, and 10.10.167.0 /24 into 10.10.165.0 /22

EdTheLad

Select all that apply. Which of the following /24 subnets can be supernetted into a larger network?

a)10.10.20.0 /24 and 10.10.21.0 /24 into 10.10.20.0 /23

b)10.10.21.0 /24 and 10.10.22.0 /24 into 10.10.21.0 /23

c)10.10.130.0 /24, 10.10.131.0 /24, 10.10.132.0 /24, and 10.10.133.0 /24 into 10.10.130.0 /22

d)10.10.164.0 /24, 10.10.165.0 /24, 10.10.166.0 /24, and 10.10.167.0 /24 into 10.10.165.0 /22

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Basically what your being asked is how can you advertise these networks using a smaller number of network bits.


a) So the question is if i advertise 10.10.21.0 /23 in my routing table will
the two routes specified be seen.

10.10.20.0/23

First look at the mask /23 i.e. 255.255.254.0
this will allow subnets 2,4,6,8,10....252
the host addresses in the first subnet 2 would be as follows
10.10.2.1 -> 10.10.3.254
and so on for each subnet after
now looking at the subnet of interest in this question which is 20
host range addresses look like
10.10.20.1 -> 10.10.21.254

a) Yes your original question will allow
10.10.20.0 /24 and 10.10.21.0 /24

b) No 10.10.21.0 /24 and 10.10.22.0 /24 cannot as in a /23 they will be
considered as 2 separate advertisements
i.e. 10.10.20.0/23 10.10.22.0/23

c) /22 255.255.252.0
subnets 4,8,12,16 .....248
so subnet 128 will have range
10.10.128.1 -> 10.10.131.254
So the answer is No as 32 and 33 are outside range.

d) Yes