After creating new subnet cannot assign IP outside of original range.

[pst133ox]

I've searched a few times for people with similar issues so I figure I must be missing something.

I recently upgraded my switches and am looking to expand the range of our network, as it is running out of room. I created a new subnet in sites/services as well as remade the DHCP scope. When I attempt to configure a machine with an IP inside this new range. (.X.X instead of .1.X) It complains that there is an IP conflict.

I'm guessing I have something configured wrong, any tips would be great!

 

[dberg35]

What are your configs IP, subnet, gateway dns?

 

[chipk]

How many addresses are we talking? What's your old scope network/mask and your new scope network/mask? If it's a private IP range, which I'm assuming it is, just post the actual IPs instead of "x.x.

 

[itsp1965]

Okay you just can't arbitrarily assign IP segments without a little design. If your network consisted of addresses ending X.X and now you have changed to 1.X, you need to take into consideration a change in subnet masking.
If you can't publish your IP settings, indicate as to whether they are a class A, B, C and provide the existing subnet mask.

Better yet, check with an online subnet calculator which will tell you if you are correctly subnetting your network

HTH

 

[pst133ox]

Allllriight. So,

I'm probably talking around 300 devices overall. I have changed the Netmask from 255.255.255.0 to 255.255.0.0, so it's net.net.host.host/16.

I guess the problem is that I am trying to re-subnet and have only altered the DHCP scope. I was assuming this was enough to allow for an address to be assigned outside of the original range. Though, being unfamiliar with the process I am uncertain.

I have not changed any DNS settings on the DC.

 

[itsp1965]

What you did here in changing the mask from 255.255.255.0 to 255.255.0.0 is essentially is now you are applying a mask meant for a class B address to a class C address which won't work. If you have 300 devices then you should change your mask to 255.255.254.0 which will allow you 510 devices.

As I have indicated before, if you don't understand subnetting, its prudent to use at least subnet calculator which will help you in determining the correct subnet masking/no of hosts for your subnets.

HTH

 

[kmcferrin]

Is there a requirement that all devices be in a single subnet? Because if you were using 192.168.0.0/24 but need more than 254 addresses you could always just add a second subnet of 192.168.1.0/24 and configure a router (or layer 3 switch) between them. That's what most people do.

I could see going to a /23 subnet if you don't want to install a router and mess with DHCP relays/BOOTP forwarders, but anything much larger than that and you'll be eating up a lot of bandwidth with broadcasts.

________________________________________
CompTIA A+, Network+, Server+, Security+
MCP, MCSA 2003

 

[pst133ox]

Well, I basically inherited a network that appears to be configured poorly in the first place.

I was under the impression that providing separate subnets decreases bandwidth requirements due to fewer broadcasts on actually physically split subnets. Though all my wires run through the same switches back to my servers.

The vision in my mind was to split our 3 floors into separate subnets (or perhaps make all printers on .1.X and laptops on .2.X and desktops on .3.X) Which would give me room for expandability and a little bit of organization.

Is this inadvisable?

 

[Davetoo]

That's fine, but you have to have some way for those three disparate subnets to talk...thus the level 3 switch or a router to connect them all together.

I'm Certifiable, not cert-ified.
It just means my answers are from experience, not a book.

 

[chipk]

Your network design should be based on traffic patterns, not necessarily location, but those two things often end up being the same.

If users on 1st floor always print to 1st floor printers and share files among themselves, it would make more sense to put them all, along with printers, and maybe servers, on the same subnet. Same goes for 2nd and 3rd floor.

If your vision was to create subnets, then changing the mask to 255.255.0.0 would not accomplish your goal. You essentially created one humungous subnet. You probably should have just done what kmcferrin suggested and add 2 new scopes to your DHCP server, and configure these VLANs on whatever is handling your layer3 routing. You'd also need to ensure that you had trunks between your switches and switch ports with specified vlan membership.

Honestly, you need to take a step back and get a design created, then have it checked, and come up with an implementation plan.

You need to know model, capabilities, and current configuration of all switches and routers, and your exact number of hosts. You need to come up with a Layer 2 and Layer 3 design for your network, and then you need to determine how to implement this design with as little down-time as possible. Re-numbering a network is no small task. If you're giong to do it, you need to do it right the first time because, as you said, it sounds like you inherited a poorly designed network.

 

[kmcferrin]

On the bright side, once it's done you should have a design that not only works now, but that makes scaling up in the future much easier.

________________________________________
CompTIA A+, Network+, Server+, Security+
MCP, MCSA 2003

 

[pst133ox]

Thanks!

It's good to hear some good advice for a change.
I guess I'll be taking a few steps back to figure out what I need and the best way to go about doing it.