Can you subnet a subnet?

danny069

This was a true/false question on my networking final exam this morning. I put down false. What do you guys and girls say?

gespenstern

Why not? Why can't you take a 192.168.0.0/24 subnet and subnet it into two /25? And subnet them further into even smaller subnets?

clarson

Subnetting is the process of breaking down an IP network into smaller sub-networks. So, true

TallDude7

VLSM. borrow bits from a subnet to make another subnet. pretty easy

Simrid

As the OP post said, a /24 can be broken down into two /25's. This is known as Supernetting.

danny069

Supernetting, wow I never heard this before. Our professor certainly did not tell us this. So technically...a subnet could be supernetted?

nman99

danny069 wrote: »

Supernetting, wow I never heard this before. Our professor certainly did not tell us this. So technically...a subnet could be supernetted?

Right, so for example if your internal network at your Main Campus consists of 4 individual /24 subnets, lets say 192.168.0.0/24 , 192.168.1.0/24 , 192.168.2.0/24 and 192.168.3.0/24, you can combine these together and create a supernet, which would be 192.168.0.0/22. You can then use this suppernetted network to maybe advertise your 4 Main Campus networks to a Secondary Site but by only using the supernet address (192.168.0.0/22) instead of 4 individual network advertisements.

Hope this helps

aschenbecher

Thats soo cool. I am loving networking.

toasterboy1

Isn't that what Variable Length Subnet Masking (VLSM) is all about. Having a /24 network and breaking down into small and also uneven groups to not waste addresses. Like /30 for WAN or Serial links and large ones for actual users.

TWX

@=nman99

I do not remember the term being used as 'supernetting' for this. I know this concept as 'route summarization'.

networker050184

It's all semantics. These days just approach everything from a bits perspective. In the real world anyway. For a test, do what the material says!

bigdogz

Bingo!!!

We have a winner!!!

To the OP:
Your professor should know Networking inside and out before he/she teaches the subject. I guess this is proof that it does not happen in all cases. Sometimes people just use the book or powerpoint slides to teach and do not take the time to learn more.

Good Luck!

fuz1on

You guys never heard of supernetting?! Easier than VLSM/route summarization to say...

CIDR = Classless Inter-Domain Routing

theodoxa

This is a bad question. While, you can take a subnet and break it into multiple smaller subnets, are you "subnetting the subnets" or just making smaller subnets from the original classful network?

BTW, supernetting is just subnetting in reverse. For example, I could take 2 /24 networks and supernet them into 1 /23 network.

192.168.0.0/24
192.168.1.0/24

---

192.168.0.0/23

It works the same as summarization.

xnx

This, it can be a method used to aggregate routes on a router too