IP address lost in DHCP


I having problems from our server that loses ip addresses. I had them as static and then one user who vpn on to our network actually took the server ip address which meant know one can access the files on that server.
As this happened i decided to reserve the ip address in DCHP but this morning it has happend again but this time no one seem to have taken the address though.

I'm not sure if this help but the Xp users can still see the filres on that server when the ip is lost but the windows 7 users cannot.

Windows 2003 SBS version
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Ayman BakrSenior ConsultantCommented:
I would suggest to run on the server with the static IP:

IPConfig /registerdns

Then on every machine having issue connecting (Windows 7) run :

IPConfig /flushdns
Post the ipconfig /all and put the static address.
Take the cable out from SBS and ping it, then check arp on machine you are trying to ping from. If there is any, compare it to mac address on SBS.

You check arp with arp -a
kwok76_ukAuthor Commented:
also another problem is losing its host name as the ip address is still there on another server when i use a network scan tool.
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Ayman BakrSenior ConsultantCommented:
If you have reserved the IP address in DHCP and your oyher server is drawing an IP address from another range then run:

 IPConfig /release

Followed by

IPConfig /renew

And verify that it has acquired a different IP.

On your original server as you have set it statically verify through IPconfig /all that it has the correct  settings and correct DNS IP.

To remove the confusion run on both of your servers:

IPConfig /registerdns

And on any machine that can't reach the server:

IPConfig /flushdns
kwok76_ukAuthor Commented:
thank you Mutawad!

I will try the above and see what happens.

Does anyone know the rule between setting up a list in the address pool and also the reservation
I attend to have the same ip address reserved and also add this into Address pool.
Address pool = -


Reservation =

will there be a conflict between the same ip address in the address pool and reservation? thanks
kwok76_ukAuthor Commented:
just to clarify:

Address pool
Start IP  and End IP
Ayman BakrSenior ConsultantCommented:
There is a big difference. A pool of IP addresses is configured on the DHCP scope to lease dynamically IP addresses from the specified pool to acquiring clients. A reserved IP is an IP which will be tied to a MAC address and can only be leased to the client with that specified MAC address.

I can see where your issue is. Basically you configured a pool with the same starting and ending IP, which in essence is one IP and you configured that same IP to be reserved. This means you dictated your DHCP to reserve the IP for your specified MAC but you also are telling the DHCP to lease that IP to any requesting client.

What you need to do is configure the pool range with IP addresses that you want your clients to get and if your reserved IP will fall within that range then you put it within the exclusions list. So the DHCP will lease any of the available IPs falling in the specified range except the excluded IPs. Then you configure a reserved IP for your server which is the intended IP tied to the MAC of the server.

The following articles will help:
kwok76_ukAuthor Commented:

On my DHCP it says The address pool is excluded from the distribution? So i assume no one should be able to take the IP address?

When i refer to Start IP and End IP its says excluded from distribution. So if i have my ip in their and also add the IP in the reservation list will this cause any issues if any? thanks
Ayman BakrSenior ConsultantCommented:
Excluding the IP from distribution and reserving it is the correct way of doing it I believe.
Ayman BakrSenior ConsultantCommented:
Well I just revised the reservation concept. Excluding an IP in a scope and reserving it will work fine as stated. However you can reserve an IP falling within the pool in the scope without the need to exclude it. Exclusions is used more for the IP which have been set manually (statically) on servers.

But since the IP you reserved for your intended server has been used already you need to release it and then you need to renew the IP on both the server you intended and the client that stole the IP. Saying that you need to also register the IPs in the DNS to correct the records. This should be followed by flushing the DNS (getting the new records) on the clients trying to connect to the intended server. All of these steps of doing it have been explained in my earlier post.
kwok76_ukAuthor Commented:
Hi Mutawad,

Are you saying i should flush the dns on the server i'm having problems with before i register the dns or flush the dns on the computer that is taken the server ip address? thanks.
Ayman BakrSenior ConsultantCommented:
Basically, You will flush the dns on the client computers that try to use the file shares on the problematic server. Flush DNS is a kind of pulling latest information from the DNS rather than use a 'cached' copy of the record.

So, first make sure that the server or client that has taken the IP from your server takes another IP by issuing 'ipconfig /release' followed by 'ipconfig /renew'. Then run 'ipconfig /all' to make sure that it has acquired a new IP different from the one you have reserved. Then you run 'ipconfig /registerdns' to replicate the changes of ip address to the DNS.

Then on your intended server (the one you want the reserved IP to be leased for) you again follow the same steps as above; that is 'ipconfig /release' followed by 'ipconfig /renew' followed by 'ipconfig' to verify it has got the reserved IP then followed by registering the changes in the DNS 'ipconfig /registerdns'.

Now you can run 'ipconfig /flushdns' to basically any client or server (including your problematic server) if it is not resolving the correct IPs.

Hope it is clear now.

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