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VLSMs?

By musijosh ·
what are the efficient steps taken when calculating Variable Length Subnet Mask (VLSM) address from a subnet address?
Given that,forexample:
The subnet address is 172.16.32.0/20,what is it's expected VLSM address ?
Thanx alot for your help.

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by G... In reply to VLSMs?

If you're splitting this one in 2 that'd be 172.16.32.0/19 and 172.16.48.0/19

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by mshavrov In reply to VLSMs?

When you specify "/20", it is the VLSM. Lets take a look into the theory:

There are 3 classes of IP addresses, available for users:

Class A: 1.0.0.0 - 126.255.255.255
Class B: 128.0.0.0 - 191.255.255.255
Class C: 192.0.0.0 - 223.255.255.255

Classfull subnetmasks:

Class A: 255.0.0.0 (or /
Class B: 255.255.0.0 (or /16)
Class C: 255.255.255.0 (or 24)

You may split the classfull network into the subnets. To do so you take bits from the "host" part and "move" them into the "network" part of address.

Old routing protocols didn't know anything about "subnets" and assumed that all network addresses are within the appropriate class. New protocols allow to submit the subnetmask along with the route.

So, VLSM (Variable Lenght Subnet Mask) is the representation of the network portion of the route.

Good luck,

Mike
CCNP, CCDP, CCSP, MCSE W2K, Security+, etc.
http://www.ciscoheadsetadapter.com

PS. "/20" is the same as "255.255.240.0"

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