Subnet mask --- broadcast domain

[Balma1969]

Hi,

This is a basic question, I'm not a network guy and I need to understand some basic staff.

Thanks in advance for your help.

In my enterprise I need to create 2 subnets to include about 200 IP each one, so I will mask the subnets  with  /24

I.E: 192.168.100.0/24 and 192.168.110/24

The question is: why not to create a /20 or /16 or something else?

I mean which is the contraindication in creating too big subnets and use only few IPs inside it?

[Flavio Miranda]

Hi @Balma1969

You can do that but there's a good practice for network that recommend to keep the network segment as smaller as possible due broadcast traffic. If you create a very large subnet, you're also creating a very large broadcast domain and this have impact on the network performance.

-If I helped you somehow, please, rate it as useful.-

[Joseph W. Doherty]

There's no problem using a large address block with only a few active hosts beyond "wasting" the address space you may need sometime in the future.

However, as Flavio has already described, when you do use a large address space (and populate it with the number of hosts it can contain), broadcasts often become a problem. This because each broadcast packet has to go to every host, and every host needs to process it (often to determine that host "doesn't care").

[Balma1969]

Thanks.

I understand that a large populated subnet, broadcast traffc  can introduce problems. But if I create a large broadcast domain and I populate it with only few members, can have impact on the network performance ? 

[Flavio Miranda · Accepted solution]

Then no of, course. What makes broadcast problem is the amount of host and not the amount of IP. Just don't make too much sense. But you can do that. I've seeing people using /22 subnetwork with no problem.

-If I helped you somehow, please, rate it as useful.-