What is Super Subnet?

[datamonitor]

Hi All,

I would like to know what is Super Subnet and how to set up? I have been told to use super subnet for following diagram;

Internet--->PIX--->ISA--->ROUTER--->CLIENTS

They told me to create a super subnet with external IP address and put it between PIX and ISA.

Thanks,

Datamonitor.

 

[Ntr0P]

If you understand subnetting, a supernet is really just a subnet in reverse. Instead of lending bits to the network side of an IP address from your host side, you take host bits from the network side.

Now that I've confused you... if you look at the binary and how it splits network and hosts, the below should help clarify the difference between subnetting and supernetting. It is also a form of route summarization. By creating a larger subnet (supernet), you can include any subnets that fall in that range. Thus, you can create one route entry in a router instead of several.


N=NETWORK BITS
H=HOST BITS

Typical class C address

NNNNNNNN.NNNNNNNN.NNNNNNNN.HHHHHHHH

Subnetted class C address

NNNNNNNN.NNNNNNNN.NNNNNNNN.NNNN HHHH

Supernetted class C address

NNNNNNNN.NNNNNNNN.NNNN HHHH.HHHHHHHH

 

[johnny99]

The explanation is correct except for one minor detail. A, B, C addresses are not used any more. Now a days we use CIDR and the you realy can't talk about subnetting or supernetting.

If you in "old times" had 16 class C addresses chunk eg. 194.19.128.0 to 194.19.143.255 your could supernet them into the network 194.19.128.0 mask 255.255.224.0.
In CIDR this would be a /20 network.

Now a days you could have a network of the same size but as 64.64.128.0 to 64.64.143.255. This is still a /20 network in CIDR but this would now be a subnet in the old class A network 64.0.0.0

 

[Ntr0P]

It's true, classful addressing is a bit of history, but it is still important to understand as many people still reference it.

That being said, if you are pursuing certification in many areas that deal with networking (Cisco comes to mind), you do need to understand and be able to work with classful and classless IP addressing. Nevermind the fact that people are still using RIP v1 which only understands and broadcasts classful IP.