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My organization is going to run out of local network IP addresses within the next few months. We are expanding to get a ton of new people and we are switching over to Lync IP phones.

Crunching through the numbers, we have about 253 addresses on the network and we are going to have over 300 IP devices. I'm not sure what I should look into to fix this problem.

I'm the server administrator, but I don't have a background in networking. I tried setting my computer from 192.168.1.XXX to 192.168.2.XXX, but it complained about a subnet issue. I left all the other settings the same as they were; subnet, DNS, gateway.

I just need to bring this up to my manager, with a couple ideas on how to fix this. Then maybe we can consult outside help if it will be to over my head. But in the meantimes I just need some ideas.

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migrated from Mar 6 '12 at 15:37

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Move your whole network to a class B or A private network address range. – Oliver Salzburg Mar 6 '12 at 15:09
That is a great idea, I thought it would need to be something overly complicated. So to do this, all I need to do is make sure that all static addresses, rules, and dhcp scope is updated, right? Then our DHCP will know how to populate the 192.168.XXX.XXX ? – poconnor Mar 6 '12 at 15:33
Yes, just change all static IPs and your DHCP range. But you're going to want to use the 172.16.XXX.XXX option I assume (or go directly to 10.XXX.XXX.XXX). – Oliver Salzburg Mar 6 '12 at 15:36
I'm pretty sure it all comes down to the defined subnet. It will just be a lot easier to set up if you use an address range that was designed to be class B or A. At least that's my understanding. – Oliver Salzburg Mar 6 '12 at 15:48
Gah, classful networking died a long time ago! – MDMarra Mar 6 '12 at 16:01

You were on the right track - use the full subnet and you'll have access to plenty of ip addresses (64k).

You'll need to expand your DHCP server to publish these addresses and possibly change your netmask to 16 ( rather than 24 (

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Things would get very messy very quickly if he actually put 64k hosts in a single broadcast domain. Simply as an exercise of Doing Things Right, he should work with smaller networks. Also, if he's introducing IP phones into the network, it would be wise for him to place those in their own subnet. – brent Mar 6 '12 at 20:53
+1. Especialyl because he could also pu the ip phoneso na VLAN and work with pioritization. I would suggest using multiple /24 networks and route accordingly. – TomTom Mar 7 '12 at 12:59
How messy are we talking about? I want to keep things extremely simple. Also what is the benefit of having phones in there own subnet? My main goal is simplest thing possible. – poconnor Mar 7 '12 at 14:42
I agree that separating your devices by subnet is a common best practice. Certain IP phones have their own DHCP service separate from your desktop/laptop DHCP server. You'll being able to separate traffic for Quality of Service issues such as downloads degrading your VoIP. – Stevko Mar 8 '12 at 0:09

*I tried setting my computer from 192.168.1.XXX to 192.168.2.XXX, but it complained about a subnet issue. I left all the other settings the same as they were; subnet, DNS, gateway."

That's probably why it complained. If you have a netmask (or a /24, pretty normal default for a 192.168.x.x IP), your host is 192.168.2.x and your default gateway is 192.168.1.x, the default gateway is no longer reachable.

There are a couple of ways of doing this, the first thing you wnat to do is to sit down and think about your probable addressing needs for the near and medium future (up to a ~2 year horizon is probably a good estimate for the planning you should do).

You'll need to make an address plan that gives enough IPs for your needs. YOu probably want to split this down into "servers", "workstation", "IP telephony" and "infrastructure management" (to the extent that makes sense). Allocate subnets that are large enough for your needs, but still small enough to not cause broadcast performance issues. I don't know how noisy Windows is on broadcast, these days, but it used to be that you didn't want more larger than about a /23 (~500 machines) in a single netblock.

You may also want to further sub-divide your network ranges by geographic location (floors, buildings).

The reason why you wnat to plan for at least a bit of future expansion is that renumbering is time-consuming (less so if you use DHCP, though), there's at least some configuration to be done (firewalls, access lists, router interface configurations, ...)

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Is this an Windows environment? If so, the subnet issue is resolved by adding this into Sites and Services and modifying the DHCP scope to include the 2nd range.

Might be a good idea now, to separate your LYNC IP phones to a separate subnet or even better completely different VLAN on the switches. Having this on a different VLAN will give you better QOS control and easier to troubleshoot when you have networking issues.

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