Clients getting IP addresses from wrong DHCP Server

Posted on 2006-11-06
Last Modified: 2012-05-05

We have a NT4 site (site A) which has a DHCP server running on a Win2K member server which issues ip addresses to clients. We have another site (site B) which connects to site A via a P2P link. Site B has a Win2k3 AD server with a DHCP server configured.
The address range that site A's DHCP server is set to issue is 195.*.*.*. Our default gateway is also in the 195.*.*.* range along with the Win2k3 server in site B. I want the clients in site B to receive ip addresses from the 192.168.100.* range but they are somehow getting there ip addresses from site A's DHCP server and not from site B.

Where have I gone wrong with the configuration or is there something else wrong such as DNS?

Help will be much appreciated.

Thank You  
Question by:aemlimited
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LVL 43

Expert Comment

by:Steve Knight
ID: 17881671
Ouch.  Does Siteb server have two network cards in?  If not where is the routing between these two sites.  If users are currently getting addresses from servera then either you have forwarded broadcast requests over a router by using an iphelper or dhcp relay setting or you have the wan connection from sitea conncted directly into their LAN?

You should have a router, be it the server or a physical device between the server down there and all it's clients.  The clients then connect to their local DHCP server first and get allocated a 192.168.x.x address.

Please clarify how it is setup at the moment, this isn;t a DNS issue, sounds like a more fundamental problem than that.  

In fact do clients at SiteB work currently.  If so please post the info. below for your two servers and a client on each site:

ip address
subnet mask
default gateway
dns server

you can get all that from ipconfig/all issues from a cmd.exe prompt on the machine



Expert Comment

ID: 17890650
Have you activated the DHCP scope by clicking activate scope (i think in tools) in your DHCP console? Windows 2003 AD server need to authorize dhcp scope before the dhcp server can lease the IP addresses to the client.
LVL 43

Expert Comment

by:Steve Knight
ID: 17890798
No way it should get an Ip from a different scope unless it is on the same subnet.  The network is configured incorrectly I think not DHCP.
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Author Comment

ID: 17964659
Hi Guys,

Steve, I think you might be on the right lines here.
Firstly, your Q (Does Siteb server have two network cards in?). Yes but one is dissabled.
We have 2 cisco routers between the sites but they have been configured to act as bridges.This was done because we were having problems with the router configuration and setting them this way solved our data flow issue between the 2 sites.
If I just put a router between our server and the router (bridge) on site B, do you think this will solve our dhcp problem?

the clients in site b do work but logging in is taking an age, sometimes 5 mins.


LVL 43

Accepted Solution

Steve Knight earned 500 total points
ID: 17964824
Yes that will be it.  A bridge is the same network....  Logging in takign an age is because AD won't know that the local DC is local because they are both on the same subnet as far as it is concerned.

I would be more tempted to sort out making the link routed rather than bridged but if you have no option you could put another router in the equation.

I really would sort out the routers though.  Each physical different site over a slow link like this should be it's own subnet with it's own IP address range and then you can define the subnets in Active Directory.

Slow logins can also be down to the DNS setup.  Each client must ONLY have DNS pointing to an AD DNS / DC server, no ISP servers at all for instance.


Author Comment

ID: 17965381
Thanks again Steve.

OK, the routers look like they are the main issue then. The reason we set them up like bridges was A, we were having problems with configuration and getting communication between the 2 sites and B, we have another site (site c) setup like this. The difference is that site a and c are NT4 and site b is win2k3.
So my issue is with AD and DNS and figuring out how to get it to work via routers.

Do you know how to configure cisco routers? I spent days with the cisco tech support people and was handed to 3 different techs before we went down the bridged route.    

LVL 43

Expert Comment

by:Steve Knight
ID: 17965709
I know roughly but don't use it often enough - there is always Cisco's free Config. Maker program or the web interface onto newer Cisco's is so much easier than the old telnet ways.  I would suggest a post here

and there are loads of very knowledgable Cisco guys there that will no doubt have a config. file for your cisco's in minutes!


Author Comment

ID: 17965747
Excellent, thanks again.

So, just to recap, you think our dhcp issue is the bridged routers and our slow login issue is probably dns.
LVL 43

Expert Comment

by:Steve Knight
ID: 17965844
Yes.... point people here for background with a link if you post over at Networking if you wish, I look at that TA too anyway.

You need to get the routers working properly in routed configuration and configure a dhcp helper / ip helper at the end that hasn't got the dhcp server which will forward dhcp requests to the dhcp server.  The two sites then need configuring in AD and subnet defining in AD sites and services.  The DC's should point to their own IP address for DNS settings in tcpip and the clients should be given their local DC's address for DNS followed by the other one by defining an option 006 (DNS) on each scope.  Likewise you define an option 003 (gateway) pointing at the local router on each site as default gateway.  The router at each site then knows your default gateway to the internet (if you have one).  The DNS server's both have forwarders configured so that reqeusts for internet based names are pushed to your ISP.


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