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Wireless Networks Thread, Running out of (private) addresses on College LAN in Technical; Hi all, We have come up against a problem, which I am sure must be fairly common, but I have ...
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    Running out of (private) addresses on College LAN

    Hi all,

    We have come up against a problem, which I am sure must be fairly common, but I have been unable to find any good documentation/guides on options, and on how best to deal with it.

    Basically, when the network at the main College site was first setup it was done using an class C IP address range (funnily enough it's not a private range, but a public one we which we no longer own and may be used elsewhere on the Internet, but that's another matter). This limits us to 254 hosts on the network.

    Anyway, with steady expansion over the years, we now find that we are running out of IP adresses (the DHCP server was regularily running out) causing serious problems with laptops/PCs not working on the network. For the moment I have addressed this by setting the lease period to 30 minutes, and we have an autoshutdown system (primarily used to save power) to to turn PCs after 35 mins of idletime (on the logon screen).

    But it's not going to keep things going for much longer, as there is need for further expansion (e.g. PCs and Wifi access points). We cannot deploy additonal access points, even though we have them, because it will tip the no. of IP addresses over the limit too often. So as you can see we are up against a problem. I have considered:

    1. Changing to IP range to private/16 (e.g. 172.16.0.0) thus giving us around 65,000 IP addresses (I think). But this sounds like a big job, we'd need to change the IP addresses on all static devices, servers.
    2. Setting up routing to split the network into two; but what is the best way/device to do this? We have a Netgear WiFi Controller which manages our WAPs. I wondered if we could use this to hand out a different range IP addresses to all WiFi devices. But having looked that the config/docs, I don't understand how to do it; not being very familar with VLANs. Netgear ProSafe support don't sound too sure either; one said we would definately need to plug the Netgear Controller into a physical router device.
    3. We do have several routers already (to route traffic to the 3 other College sites), would it be feasible to use one of these? I'm not sure but with them being very old, their Ethernet ports may only work at 10Mbit (10BaseTX) so it may cause a bottleneck.

    I just wish there was some simple, not too expensive, hardware device with 2-3 ports which could be used for this purpose.

    One underlying concern with the routing option is how the other routers on the network will find out about this new subnet. Would this happen through some automatic routing discovery protocol? Can this be done by just tick a RIP tick box somewhere? Even though I think our routers use a new protocol than this.

    Sorry this is turned out to be very long.

    Any advice much appreciated!

    Many Thanks,

    Bruce.
    Last edited by Bruce123; 24th May 2009 at 11:07 PM.

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    localzuk's Avatar
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    I think your best, and simplest, option is a new range. It's a big job, but as you say you only have a few hundred devices, it won't be that big a job.

    Any routing etc... seems like making a simple problem into a complex one.

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    FN-GM's Avatar
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    hanging to IP range to private/16 (e.g. 172.16.0.0) thus giving us around 65,000 IP addresses (I think). But this sounds like a big job, we'd need to change the IP addresses on all static devices, servers.
    It depends on the subnet mask, if you use it at 255.255.0.0 you will have 65534 addresses to use. I would cansider what subnet mask you use to suite your network. Will use have that many devices on the LAN?

    This will help - Online IP Subnet Calculator

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    Quote Originally Posted by FN-GM View Post
    It depends on the subnet mask, if you use it at 255.255.0.0 you will have 65534 addresses to use. I would cansider what subnet mask you use to suite your network. Will use have that many devices on the LAN?

    This will help - Online IP Subnet Calculator
    I was looking at a subnetmask of 255.255.0.0. We don't actually need 65K IP addresses, it's just that /16 is the next step up from a /24 range, which we are on.

    One other reason for totally changing the range (which I didn't mention) is that some MS software considers our range as "external" to our Intranet, presumably this is because it isn't within any of the private ranges specified in RFC1918.

    But I'd really prefere to not change range just yet, as I have a feeling that it get really complex and time-consuming, but we may have to.

    Thanks,

    Bruce.

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    amfony's Avatar
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    sounds like you need to incorporate some segmentation IE Vlans IE subnets IE routing .. sorry you will need this.

    If you are running out of IP's on a /24 network then you are only using max ~250 devices. Believe it or not this is not that many devices (as in, if you are using dhcp for clients then the static devices would probably take up %10 of your scope - therefore about 25 devices to manually configure, it could be worse!)

    Going from /24 network to a /16 just to get more ip addresses is - what i believe - the totally wrong way to skin this cat. What you need to do is segment your clients from your servers, your Wifi Clients from your wired etc. By segmenting you increase the number of network you are actually using. Using these new networks will ofcourse increase your available IP Pool by (if /24) ~250.

    I understand that this can be sticky (if your not comfortable with lan engineering so to speak it will be pretty tough troubleshooting) but routing/vlan-ing is the correct fix for this problem.

    Sorry for the "bad" news.

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    FN-GM's Avatar
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    Without changing your range for servers etc the only things you can really do are:

    1. Shorten your lease time more
    2. V-lan you network give each switch its own ip range. Keep your current IP range for devices with static addresses. You can only do this if you have layer 3 switches.

    EDIT: beat me to it
    Last edited by FN-GM; 25th May 2009 at 12:25 AM. Reason: extra

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    EDIT: beat me to it
    Amfony FTW!

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    garethedmondson's Avatar
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    Quote Originally Posted by amfony View Post
    Amfony FTW!
    I've never dealt with setting up IP ranges. OUrs were given to us but the LEA - but would changinfthe range help your situation?

    We use 10.180.8.1 - 10.180.15.253 on a subnet of 255.255.248.0 and it gives us a lot of addresses. I'm sure someone could tell me how to work this out (please - somebody tell me how to work it out).

    Best wishes

    GJE

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    FN-GM's Avatar
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    Quote Originally Posted by garethedmondson View Post
    I've never dealt with setting up IP ranges. OUrs were given to us but the LEA - but would changinfthe range help your situation?

    We use 10.180.8.1 - 10.180.15.253 on a subnet of 255.255.248.0 and it gives us a lot of addresses. I'm sure someone could tell me how to work this out (please - somebody tell me how to work it out).

    Best wishes

    GJE
    Sorry but whats the question?

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    localzuk's Avatar
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    Quote Originally Posted by amfony View Post
    I understand that this can be sticky (if your not comfortable with lan engineering so to speak it will be pretty tough troubleshooting) but routing/vlan-ing is the correct fix for this problem.
    Routing with his current range would be pointless - as he needs more addresses. So, what he needs to do is use new range(s) AND use vlans/routing. Routing on its own will make things more complex unless using a well thought out set of IP address ranges.

    And also, he could easily go from a /24 to a /22 if he wanted... Which would give him 3 times the IPs. There would be no need to go the whole hog and use a /16.

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    Edu-IT's Avatar
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    Quote Originally Posted by FN-GM View Post
    Sorry but whats the question?
    How many addresses can he have?

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    Quote Originally Posted by Edu-IT View Post
    How many addresses can he have?
    ah right, he has 2046

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    garethedmondson's Avatar
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    Quote Originally Posted by FN-GM View Post
    Sorry but whats the question?
    I don't know. Been drinking. I just wondered if changing the range would help the original poster. I'd better go because we are on our third bottle of wine and this isn't good. LOLOLOL.

    Soz people.

    GJE

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    garethedmondson's Avatar
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    Quote Originally Posted by FN-GM View Post
    ah right, he has 2046
    Yes - I think I was asking people to tell me how to work that out.

    GJE

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    amfony's Avatar
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    Quote Originally Posted by localzuk View Post
    Routing with his current range would be pointless ...
    ... and impossible

    Quote Originally Posted by localzuk View Post
    So, what he needs to do is use new range(s) AND use vlans/routing.
    which is implicit (sorry for skimming over this)

    Quote Originally Posted by localzuk View Post
    ... he could easily go from a /24 to a /22 if he wanted... Which would give him 3 times the IPs.
    and expand the broadcast domain x3? Would you recommend this in any production environment?

    Getting back on point i think that the OP has hit a critical mass on his/her network. This is the time to set things up the "right" way opposed to band aid fixes. However ofcourse its mid term (here i assume there aswell).

    Tough situation - maybe the subnet mask change IS the right choice here for a temporary solution?

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