Subnet mask change good idea?

[ploughingon]

Hi

I'm kinda the only one that approaches an understanding of tcp/ip at my work place, but i'm a very long way from being an expert. We're running out of IP's in our address space, I've got an idea on how to sort it out and I'd like to run it past the more experienced folks on this forum.

we use 172.16.4.0 / 255.255.252.0 at the moment. Gives us 1024 address's
of this range 172.16.4.0 - 172.16.5.254 is managed by dhcp and
172.16.6.0 -172.16.7.254 is the range we assign to servers printers , switches etc.

I've been looking for an easy way to expand this range. So i figured that changing the subnet mask to 255.255.248.0 bringing 172.16.0.0 - 172.16.3.255 into the range. Would be the best thing to do for us.

I'm kinda nervous as I've never managed a broadcast domain of this size before and i dont really know what to expect.

Am i mad or is there a gotcha?

 

[burtsbees]

Do you only have one router? What's the topology like? You could separate all the broadcast domains using VLANs, like router-on-a-stick, and more subnets with a 172.60.x.x/16, using vlsm (subnetting a subnet). Also, if you choose to have a broadcast domain this large, are you using any broadcast storm control, or PIM?

Burt

 

[brianinms]

The best thing you could do is go back and change your subnets on everything to a 24 bit mask 255.255.255.0. For this many hosts you clear need and/or should have a core switch that routes layer 3.

 

[ploughingon]

Hi Burt

Thanks for taking an interest.
The topology on this subnet is pretty flat, everything comes back over a fibre back bone to a beast of a core switch. This acts as the default gateway for the current 172.16.4.0 network.
I've thought about vlans and "one subnet per floor", but I wont be here forever and the boss has asked me to keep it as simple as possible.
On top of that theres a whole bunch of services that the apps team are paraniod wont work if i go start changing IP's ...thats why i looked at just changing the subnet mask.

I am concerned about broadcast storms tho,
I'm not familiar with techniques to stop them or even at what point broadcast traffic really becomes a problem. I've never admind a network that was large enough or slow enough for it to be an issue. Is 2000 address to much for one address space do you think ? We've got good nortel kit throughout and broadcast traffic is pretty low at the moment.
Bear in mind we are not suddenly gonna have 1000 extra devices shouting from the off , I just want to get some head room and this seemed the easiest route.