Question

dhcp turned on in wireless

Asked by: 05fdml

New user has a LAN of about 50 people. Every once in a while ips will overlap. All servers have manual ips. all laptops have dhcp turned on.

The firewall is the dhcp server (conflict detection is on). Windows is the dns server.
The current setup also has the dhcp server turned on in the wireless. (DDWRT i believe) I believe that is the culprit as the wireless device is conflicting with a manual ip.

There should only be one dhcp server in the network, though i am getting resistance to that. as they dhcp on the wireless has never caused problems before

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Asked On
2009-09-10 at 14:43:05ID24722999
Tags

dhcp

,

wireless

Topics

Windows Networking

,

Wireless Network Cards & Adapters

Participating Experts
3
Points
500
Comments
5

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Answers

 

by: globalonline2Posted on 2009-09-10 at 14:47:15ID: 25304851

Check to make sure someone else doesn't have another router plugged into the network.  If you go to one of the "duplicate IP" machines and browse to the default gateway you'll be able to see what kind of router it is.  I bet someone has a rouge DHCP/router jacked in.

 

by: mds-cosPosted on 2009-09-10 at 14:48:37ID: 25304864

Not necessarily.  Some people intentionally set up multiple DCHP servers for redundancy.  This is more applicable to a home network where low end devices are more likely to blow up or get shut off.

The easy solution without fighting the resistance is to modify DCHP on the wireless so there is no overlap.  For example, let the wirless serve out x.x.x.100 - 175 and let the firewall serve out x.x.x.176 - 250.

As far as "we never had problems with it before"....well just because it never bit you before does not mean it was right to begin with!

 

by: MaestroDTPosted on 2009-09-10 at 15:03:38ID: 25304994

I agree with mds-cos.

However I believe you should segment the network as follows:

Wireless: x.x.x.50 - 100
Firewall: x.x.x.101 - 150

Save the IPs below .50 for static assignments, such as your manually configured servers.
Save the IPs above .150 for other static assignments or for future expansion/applications.

Since you said your LAN only has 50 people, I don't see any reason to assign more than 50 addresses from either DHCP server.

 

by: 05fdmlPosted on 2009-10-14 at 14:23:40ID: 31627327

correct answer

 

by: mds-cosPosted on 2009-10-15 at 07:20:27ID: 25580755

Um, wow???

Specific IP addresses used have absolutly no meaning outside your network.  I've worked with guys who always, always, always put DHCP addresses from 100-200 and will argue up and down that is where they "belong" (these guys all obviously work in small networks where 100 IP addresses are enough).

I've worked with others who always put their DHCP on the "low" end and others who always put it on the "high" end.  Sadly, I've even walked into too many networks that had no apparent plan whatsoever to their IP address scheme.

So put your DHCP as I suggested or as MaestroDT suggested or wherever works for you and your network.  The important part is that you have some sort of plan for IP (e.g. servers go in this range, printers in that range, network devices here, DHCP there, etc...).

I do have to humbly disagree with MaestroDT on "don't see any reason to leave any more" since you currently have only 50 computers.  When planning IP address space you should never look at "what do I have today" and plan just for that.  Make room for growth!  If you have 50 computers now, make your DHCP pool larger than that so that the 51st computer does not have you running a support call.  Or if somebody connects their personal laptop or smart-phone, you don't want to be left figuring out why one of your computers is not getting an IP address.  If you have 1 server, leave space when planning the sever range for adding more.  The last thing you want to do is re-engineer your IP address scheme just because you didn't consider growth.  On a "class C" IP space (where your IP mask in 255.255.255.0) you have 254 available IP addresses.  There is no reason to get stingy with the space, and every reason to plan for growth or unforseen devices.


P.S.  You should have given me points on this question ;-)

20120131-EE-VQP-002

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