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Help Server 2008 DHCP address aquistion problems

Posted on 2012-04-06
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Last Modified: 2012-04-10
We have a server 2008 domain and for some reason client machines randomly have ip conflict problems.

What'll happen is a user will log on and when if they lost their address for some reason the computer(windows 7) will start with a address towards the beginning of the scope belonging to another client. Then it sees the conflict and tries the next address in line, going form say 192.168.54.90 to 192.168.54.91. This process will continue all the way up the scope until it reaches an available address. This can sometime take half an hour.

The way I understand DHCP to work is the client should be requesting an address for the server. The server should then reply with the next available address in the scope. Instead the client just continues to try addresses sequentially which is a very long process.

Correct me if I'm wrong, if not is there something I can change in the settings to fix this?
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Question by:ja5on
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Expert Comment

by:Geodash
ID: 37816576
Check out this article. I think your DHCP and DNS are not talking correctly? Are you scavenging?

http://social.technet.microsoft.com/Forums/en-US/smallbusinessserver/thread/4f12cc07-5d42-4d78-942e-8932902ac43f/
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Author Comment

by:ja5on
ID: 37816580
Yeah scavenging is set.
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Expert Comment

by:Geodash
ID: 37816582
What is the lease duration on your Scopes?
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Accepted Solution

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Raquero earned 500 total points
ID: 37816591
Sounds like your lease time may be too short. You can also enable conflict detection on the DHCP server so the server will check if an address is available before offering it to a client.

Is DHCP running on a 2008 server? Yes, enable conflict detection.
What is the lease time for the DHCP scope(s)? Shorter than say 7 days? Increase lease time.
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Author Comment

by:ja5on
ID: 37816595
Yeah its 3 days...I will change to 7 and check the other DNCP settings

thanks guys :)
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Expert Comment

by:Geodash
ID: 37816596
Yes, minimum 7 days - which should be OK if you don't have a HUGE amount of clients
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Author Comment

by:ja5on
ID: 37816603
This site has a range between 100 and 120 depending on how many customers we have on site.
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by:Geodash
ID: 37816605
you should be fine going to 7 days to test
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Expert Comment

by:Raquero
ID: 37816611
The MS default for a new scope on 2008 is 8 days but 7 is fine as a minimum. You can even make it longer if the environment is fairly static (mostly desktops for example).
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Expert Comment

by:Raquero
ID: 37816623
How many visiting client computers  (vis. customers) do you host on average?
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Author Comment

by:ja5on
ID: 37816639
Sometimes we have up to 20 or 30.

Now I have a triangle with a yellow exclamation point. It may have been there before but didnt notice it.

Its next to the IPv4 icon and the Scope folder icon. Any Ideas? Running out of addresses maybe?
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Expert Comment

by:Raquero
ID: 37816668
Assuming you are referring to the scope, the warning indicates the address pool is >90% allocated. You may need to experiment with lease times a bit so the server releases the ones assigned to customers.

Another approach is if the customers attach via wireless and not wired, consider configuring a separate subnet for the wireless network. We do that with a 1 day lease time on wireless and 7 days on wired subnets and it works great.

If that is not an option, you can use a shorter lease time (< 7 days) but be sure to enable conflict detection on the DHCP server (not enabled by default). After turning on conflict detection, if you see entries labeled "BAD" you can delete those so the server can re-assign them if the client that had that IP address is no longer on the network.
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Author Comment

by:ja5on
ID: 37816711
BAD_ADDRESS?
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Expert Comment

by:Raquero
ID: 37816735
Yes. With conflict detection enabled on the server you can safely remove those entries from the Address Leases folder. If any reappear it indicates a client on the network that is using an IP address within the DCHP scope that was not handed out by the server.
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Author Comment

by:ja5on
ID: 37817344
Sweet thanks so much for all your help.
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Expert Comment

by:Raquero
ID: 37817459
Happy to help and glad your issue is resolved.
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Author Comment

by:ja5on
ID: 37828076
Hey guys sorry for the late response things can get hecktic around here. :) So today I checked my dhcp server and the Scope is filling with BAD_ADDRESS. I can ping those addresses and no response

Any Ideas?

Thanks again for all your help.
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Expert Comment

by:Geodash
ID: 37828088
I assumed this question was closed because you already awarded points.
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Author Comment

by:ja5on
ID: 37828100
Sorry I commented because I thought it could be related.

I'll start a new thread...
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