splitting up a /23 "super"-net

[ljoenens]

Hi,

Has anyone experience with networks with networks mask of /23 ?

Question/discussion is actually if a /23 network has significant benefits by splitting it up to two /24 subnets.

As everyone knows, the smaller the subnet, the smaller the broadcast domain, the better the LAN trougput & efficiency due to less packet collisions.

But is it really worth splitting a /23 up into two /24 ? I can imagine for bigger network, but not sure if it's worth the trouble for just a /23 network?

Any advise from experienced eng. are most welcome!

Thx.

Lieven

[danbowencisco]

Hiya,

There is no benefit really except for route aggregation. Depending on your routing protocol, it will only have to advertise a single /23 instead of two /24 networks, which means smaller routing updates. If you wish to control traffic between devices on this /23 network, then subnet it, if not I wouldnt bother.

HTH,

Dan

[Jan Hrnko]

Hi,

Question/discussion is actually if a /23 network has significant benefits by splitting it up to two /24 subnets.

Well it really depends on the situation, but changing from /23 to two /24 can improve the throughput somehow, because you reduce one bigger broadcast domain to two independent broadcast domains.

As everyone knows, the smaller the subnet, the smaller the broadcast domain, the better the LAN trougput & efficiency due to less packet collisions.

I can't agree on that if you are not using hubs. And if you are NOT using hubs, (you use switches,routers...) there just aren't any frame collisions happening. As you know, every switch or router port is separate collision domain.

But is it really worth splitting a /23 up into two /24 ? I can imagine for bigger network, but not sure if it's worth the trouble for just a /23 network?

Exactly as you have said. If there is a bigger network with more machines and lot of traffic or too many broadcasts or multicasts going on then you could consider splitting the /23 into smaller segments divided by their use.

Best regards,

Jan

[ljoenens]

Thanks all for your valuable input.

To give you more details; we're going to use 3750 switches, definetely no hubs!

A separate vlan for VoIP, Video, IP cameras, will also be used as to allow QoS/CoS and keep the DATA vlan (the famous /23) only for PCs'laptops and printers.

BR,

Lieven

[Jan Hrnko]

Hi,

If you plan your network like this, I suppose that /23 subnet should be ok, but if you do encounter high ammounts of broadcasts in your network you can still then divide the /23 subnet into smaller subnets...but it really depends on behavior of the users in your network.

Some times ago I was responding to a guy who had cca 800users and 30servers in the same vlan and he wanted to separate them into /24 vlans mainly to higher the throughput and increase performance. He ended up having users divided into more /24 subnets and implementing Inter-VLAN Routing.

Best regards,

Jan