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Home > Forums > MIS/IT > DNS / BIND / DHCP Issues > DNS/BIND/DHCP/WINS Issues > FAQs

DNS/BIND/DHCP/WINS Issues FAQ

DHCP

Troubleshooting DHCP

faq950-5135

Posted: 15 May 04 (Edited 24 Jan 05)

Troubleshooting DHCP problems is not really rocket science.  Just a few simple steps to make sure everything is configured properly.  If you have a client that is not connecting to the network, start at square one.
The Client  -  Run ipconfig /all and see what the ip address is.  If it’s 169.254.x.x, then the client can’t connect to a DHCP server.  (Check your cabling and the nic.)  This could save you a ton of work down the road.  Next, check the software, make sure TCP/IP is still installed and make sure obtain an ip address automatically is checked.  If this is correct, move onto The Server part 1.
The Server, Part 1 -  If the problem is only on w2k pro machines or later, make sure all the options needed have been configured at either the server or the scope level.  W2K servers support so many os’s, there are some that are meant for systems other than W2K, and W2K can’t use.   Make sure the appropriate options are chosen.
The Server, Part 2 – If the client’s can connect to the network but still can’t receive an IP address, this is another place to look.  Make sure the DHCP server is a part of the same scope.  You can’t use a server with an IP address with an address of 10.0.0.0 while the clients are looking for 192.0.0.0.  It just won’t work.
The server, Part 3 – Check and see if the clients are on a different LAN from the server.  If they are, make sure you have a DHCP/BOOTP relay agent installed and functioning correctly.
    A) Place the relay agent on the client side of the LAN.
    B) At the server, create a scope for the other LAN.
    C) Make sure the subnet mask is the same correct for the remote LAN.
    D) DO NOT, I REPEAT, DO NOT include this scope on any superscopes where the Server is located.
The Server, Part 4 – Multiple DHCP servers.  A real no-no.  This is especially true if you are running Small Business Server.  Once SBS finds another DHCP server on the same scope, it stops issuing IP’s.
The Server, Part 5 – Make sure the DHCP service is running.  Might sound simple, but sometimes the simple stuff is what throws you.  Open the DHCP console and see if it’s running.  If it is, stop it by clicking on the stop button up in the toolbar, then start it again by clicking the start button.  If it’s not running, there has to be a reason.  Here you move onto your event logs and see what stopped it.
The Server, Part 6 – Incorrectly reported lease expirations.  If the scope is set to infinite, the reserved clients are set to infinite.  The reserved clients use the least time set at the scope option.
The Server, Part 7 – Make sure your server isn’t using Broadcast to client messages.  This will slow down network activity and just isn’t correct now.  Back in the old days, times were different.  Go to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\DHCPServices\Paramaters\IgnoreBroadcast Flag on the server and set this to 1.  This will cause the server to ignore broadcast requests from the clients.
The Server, Part 8 – Server is not giving out address leases for a new Scope.  If you need to change a scope or create a new class to accommodate new clients, you must create a new scope on the Server containing the new range of IP Addresses.  If the clients aren’t getting addresses from the new scope, you need to one of two things.  Create a superscope that includes both scopes, or add a new IP Address in the TCP/IP properties on the server to include the new scope.  You can leave the old IP address of the old scope in the advanced options of TCP/IP.

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