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Facing a problem where we are running out of available network addreses, we are currently on bog standard 192.168.1.x range.

Reading about making more ips available and subnets and think i have just about got my head around it.

My question is, is it as simple as saying to my router (currently handling dhcp) use ip range 172.16.0.1 / 255.255.254.0 and it should hand out ips from 172.16.0.1 to 172.16.1.255? all of which are able to talk to each other?

Or have i got wrong end of stick here? On basis of above is there a way of staying on 192.168.x.x and getting more hosts, we are currently using too many but expansion plans wont see more than another 100 at most in next 5 years.

if you need any more detail please let me know.

Thanks

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Is EVERYTHING on your network DHCP assigned? Man I hope not. –  Chopper3 Jul 25 '13 at 13:15
    
no we have 1-100 which handles all the printers and servers and unfiltered internet access, the dhcp and filtering is from 100-254. The network was inherited as i have just started a job here –  Ben Gillam Jul 25 '13 at 13:30
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Could it be that you read some old documentation using classful addressing (pre-CIDR)? You do not need to switch from 192.168.x.x to 172.16.x.x anymore just to have subnets larger than /24. Only if you want to have more than /16 (the address range starting with 172.16.0.0 is /12). –  Dubu Jul 25 '13 at 13:31
    
@Chopper3 How is manual static IP configuration better than automatic, managed configuration? Especially when talking about readdressing where its simple change on the DHCP server instead of a day long mass manual reconfiguration –  TheLQ Jul 29 '13 at 4:34
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@TheLQ - we've done this to death on here before - basically because if your DHCP server goes down you're in trouble and if something else on the same network starts acting as a DHCP server you're in trouble. Both of these things have happened multiple times to people coming to this site for help. Yes DHCP makes sense for clients, maybe even printers but it's just laziness for servers and opens up routes to outages. There is an exception however, the use of vApp derived dynamic IPs on vSphere where there's almost zero chance of these outages happening. –  Chopper3 Jul 29 '13 at 11:19
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2 Answers

up vote 4 down vote accepted

RFC 1918 identifies a number of private address ranges, including 192.168.0.0/16. This block includes all addresses from 192.168.0.0 to 192.168.255.255, which ought to be sufficient for your network.

You're currently using 192.168.1.0/24, which is a block of 254 addresses. If you subtract a bit from the network mask -- 192.168.0.0/23 -- you'll double your available addresses. Your range will extend from 192.168.0.0 to 192.168.1.255. That corresponds to a "netmask" of 255.255.254.0.

You'll get the same thing using 172.16.0.0/23, which is what you've identified in your question. Same number of addresses, just a different range of numbers. Note that according to RFC 1918 that block is bigger; 172.16.0.0/12 includes over 1,000,000 addresses.

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Thanks, that would be more ideal. From a DHCP point of view, if i told it to hand out with subnet mask of 255.255.255.254 starting with 192.168.0.1 is it smart enough to work out the rest or do i have to have something telling it to route between the two? - Sorry if I sound daft, never had to get that deep into networking so far so this will be a good learning experience. –  Ben Gillam Jul 25 '13 at 13:41
    
There is no "routing" to worry about; everything is on the same network. –  larsks Jul 25 '13 at 14:24
    
You should be aware of the implications of creating broadcast domains larger than /24, though. It will work, but it would be more ideal to create a new subnet and use routing. –  James O'Gorman Jul 25 '13 at 14:51
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...although by that logic, you should be aware of the implications of using anything large than a /28. Seriously, there's no magic number; if you have a bunch of systems on the same network segment that generate lots of broadcast traffic it can impact performance, but only you can determine whether or not this is a problem. –  larsks Jul 25 '13 at 14:52
    
thanks for the advice - this may not be the final setup but enough to keep us going for now, they are looking at moving to a new building to grow further at some point, will give me a chance to make sure the cabling is less of a mess too and hopefully get some investment at the time, at the moment everything is on £0 budget at the moment (annoying) so trying to make best of what we got and put in proper expansion plan when i have time to think it out, only at end of second week here and barely sat down very busy :P - Have a great weekend –  Ben Gillam Jul 26 '13 at 9:27
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You could migrate from 192.168.1.0/24 to 192.168.0.0/23.

min ip will be: 192.168.0.1
max ip will be: 192.168.1.254

With such subnet there are 510 hosts will be available

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