Supernet question

Answered Question
Apr 10th, 2008

Hi. I was just analyzing the concept of using VLSM and supernetting and i was just a bit confused over some details.

Before anything else, if i have a subnet of 192.168.0.0/30 used for a pt. to pt. serial interface, can i assign a subnet of 192.168.0.0/28 on an e0 interface for example? If not, then shouldn't i just use a standard subnet of /28 instead? Meaning that i assign a subnet of 192.168.0.0/28 on the serial interface and 192.168.0.16/28 on the e0 interface.

I have this problem too.
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Correct Answer by Jon Marshall about 8 years 7 months ago

No you can't use 192.168.0.0/30 and then 192.168.0.0/28 on different interfaces. But you can do

192.168.0.0/28 on the ethernet interface and then

192.168.0.16/30 for the P2P serial link.

This would not be a good example of using VLSM within a class C though.

For P2P links it's often best to start at the end of the subnet range and work backwards ie.

192.168.0.0/28 for ethernet interface

192.168.0.252/30 for serial interface.

This gives you more flexibility in splitting up the class C network.

Jon

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Correct Answer
Jon Marshall Thu, 04/10/2008 - 05:46

No you can't use 192.168.0.0/30 and then 192.168.0.0/28 on different interfaces. But you can do

192.168.0.0/28 on the ethernet interface and then

192.168.0.16/30 for the P2P serial link.

This would not be a good example of using VLSM within a class C though.

For P2P links it's often best to start at the end of the subnet range and work backwards ie.

192.168.0.0/28 for ethernet interface

192.168.0.252/30 for serial interface.

This gives you more flexibility in splitting up the class C network.

Jon

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