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IP address from mac address

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11 replies

by trockii

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I am a Network administator using Windows 2003 SBS. I am having a problem with my DHCP service. I have it set to start automatically, however throughout the day it stops and I have to restart it manually. I was told it's because there's another device on the network with the same ip address. If I ping the ip address I get my server not the machine kicking me off. None of the machines are showing an IP conflict, but I do have 50 IP phones on the network. I don't know how to see their IP address, just their mac addresses. Can anyone help me fix this problem? Thanks

11 replies

by douglasb

This won't help, but I am running SBS 2003 and have the same problem. I was told the DHCP service will not start automatically, you have to start it manually. But when I do a manual start, it starts and stops right away. I disconnect the server from the network and it starts and stays running, however, if I reboot a work station it won't pick up an IP. I ended up having to assign an IP to each machine. I would think if you had an IP conflict you would get a notice . . .

by jdclyde

It "should" give a notice if another device shows up on the network with the same address.

Try changing IP and them ping the address. If you get a response then there is a second device sharing.

Have you checked the pool range?
Does it have enough IP's assigned to it to handle all users?

by curlergirl

Two pieces of advice:

1. If your Win2K3 server doesn't have a static IP address, it should. You should never have a server set up to get its IP address from DHCP.

2. In the configuration of your DHCP server, you should have the IP address(es) of any servers or routers excluded from the range. You set up an exclusion for just this purpose - so that no other device on the network can possibly get the same IP address as your server(s). For example, if your IP address range is 10.0.0.1-10.0.0.254, and you have a server with address 10.0.0.2 and a router with 10.0.0.3, you might want to set up an exclusion range of 10.0.0.1-10.0.0.5. If you don't have such an exclusion range set up, do so right away, and this should resolve any problem with another device getting the same IP as your server.

If you simply want to find out if DHCP has assigned the same IP as your server to another device on the network, open the DHCP management console and look at the Address Leases section - this shows you a list of every device and the current IP address that it is using. Of course, the DHCP service has to be running to do this...

Hope this helps!

by maniskid

In addition to reserving your dhcp server's ip address. If you want to ping the ip address of the machine that is replacing your server you have to flush the dns: type "ipconfig /flushdns"

What is happening is that your ping request looks at your local computer's cache and returns a result, and unless its purged it will give you a false reading. So clear it. Notably, the DNS server will have a record because the DHCP server would have put it there, you can check there and refresh and it should turn up an "A" record of the other machine.

To find the ip's of the phones, I am not sure but I think "arp -a" will do the trick, or something similar.

If you really want to find out the ip of a phone, i suppose that you could load 'network monitor' then make a call (just a thought)

This behaviour reminded me of standard win2k3 server behaviour....
http://www.microsoft.com/resources/documentation/WindowsServ/2003/standard/proddocs/en-us/Default.asp?url=/resources/documentation/WindowsServ/2003/standard/proddocs/en-us/sag_dhcp_ovr_security.asp

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