mixed up IP address assignment

[z4ydi]

We run DHCP services for both curriculum and Admin network on the same server.

We have recently changed our IP address scope for curriculum network because it was running out of IP addresses. However after the change our curriculum PCs are now randomly picking up Admin IP addresses (some PCs receive CURRICULUM IPs and some admin IPs in the same class room feeding from the same switch). We then have to do IPRELEASE and IPRENEW, to force these PCs to pickup curr IP; but this keeps hppening over and over, please advice if you know why.

[SYNACK]

How do you have the allocation bit set up, if you are on multiple subnets with a router in the middle the address should be given from the DHCP pool that applies to the router port that the machines are connected to.

 

I think we may need more details about how your network is layed out and how your DHCP is set up to answer this one.

[Heebeejeebee]

Have you tried flushing the dns on these machines? (ipconfig /flushdns after releasing the ip address.)

 

HBJB

[z4ydi]

Well the DHCP for both Admin and Curriculum was configured on the same server and we had no problem for the past few years, as we started to run out of IP addresses all I did is to delete the old Curriculum scope and create a new scope with bigger IP range, after the change this IP mixup is happening. here is the configuration for both admin and curr on the same server.

[SYNACK]

That config looks right but in order for the server to know which address to give which group of clients it must have some way to distinguish them. This is usually done with something that handles routing and DHCP helper forwarding.

 

When you changed your ip address ranges if you did not also change this mechanism to the new address space the server will not know which range to allocate addresses from for which pcs.

 

Have you checked to see if routing and possible VLANs are enabled on your core switch and do curriculum and admin machines plug into different switches.

 

I would look for the core point of routing in the internal network as this is where the problem is most likely to be.

[z4ydi]

That config looks right but in order for the server to know which address to give which group of clients it must have some way to distinguish them. This is usually done with something that handles routing and DHCP helper forwarding.

 

When you changed your ip address ranges if you did not also change this mechanism to the new address space the server will not know which range to allocate addresses from for which pcs.

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I think this is where the problem is too. The server that is hosting both scopes has 2 network cards one for 10.8.98.0 range and the other for 10.8.100.0 range but I do not know how to bind the right scope to the right network card. please some one help me.

[SYNACK]

As long as the two network cards are each addressed as part of the required address pool and the DHCP server is set up to bound to both cards. This is located under the server objects properties in the DHCP MMC (after you have clicked the plus beside the server) it is under the advanced tab in a button called Bindings.

 

It should then it be able to work it out as it will be able to see which network address the request was received on and knows from that what pool it is in.

 

The question still remains, are the staff and students connected to different switches, if they are not then you may still have VLANs set up on the switches that you have to deal with.

[z4ydi]

We have separate switches for admin and curriculum. yet PCs which are feeding from the same curriculum switch, in random receive some ADMIN IPs and some PCs receive CURRICULUM IP addresses. the 2 networks are separated at the router level.

[SYNACK]

First I would double check the networks have not become accidentally patched together, I would do this by manually setting a curriculum pc to an admin ip an leave it on a curriculum switch then try to connect to an admin resource. If you can your networks are linked somewhere and you need to go hunting through patch leads.

 

If not then double check that the router is setup for the new ip range fully. Including the dhcp ip helper addresses, the router interface addresses and subnet masks and even the routing protocols.

[z4ydi]

First I would double check the networks have not become accidentally patched together, I would do this by manually setting a curriculum pc to an admin ip an leave it on a curriculum switch then try to connect to an admin resource. If you can your networks are linked somewhere and you need to go hunting through patch leads.

 

If not then double check that the router is setup for the new ip range fully. Including the dhcp ip helper addresses, the router interface addresses and subnet masks and even the routing protocols.

 

But when I give a PC an Admin IP and then put it on a curriculum switch, because the curriculum domain controller which is hosting the DHCP services has 2 network cards; wouldnt this allow routing between the 2 networks anyway.

I have still tried the same and yes I can ping any admin machine. and we only have one router that connects both networks to the internet.

[SYNACK]

Ah well it could be doing routing as well but this does not invalidate the test. If your networks were properly segmented with the router/server as the only point of contact you should not have been able to access the admin side from the curriculum side using an admin address.

 

This is because if it is setup with an admin address on the curriculum side then it should be on a different subnet to the curriculum router interface because of this the router interface will not even accept the packet for routing. For ip connectivity the devices must be on the same subnet and if this was, as it should have been the only admin ip on the curriculum side there should have been nothing that it could talk to.

 

Just to be sure make certain that there are not any extra ip addresses configured on the DHCP servers curriculum network card that are set differently to your curriculum scope.

 

Quickest way to do this is with ipconfig /all in cmd

[z4ydi]

the IPs are correctly assigned on both NICs. should I call our ISP, and find out from them whether they have misconfigured our router maybe?

[SYNACK]

the IPs are correctly assigned on both NICs. should I call our ISP, and find out from them whether they have misconfigured our router maybe?

 

If your router only handles your internet and only has one port to plug into your network then I doubt that it is the cause of your problem.

 

From what I can see your two isolated networks have become linked together somewhere, probably by a stray patch lead. Your problem definatly sounds like it is internal and the above is the most likely cause. You should go through your cabinets and check for cross patching between curriculum and admin switches

[z4ydi]

but the funny thing is that when I checked the Admin PCs non of them has picked up curriculum IP. If the 2 networks were cross linked then the same problem should have exist on the admin network too, dont you think? i mean some of the Admin PCs should have picked up curriculum IP.

[SYNACK]

It depends on which side is fastest to offer an ip address, if the switching links are faster for admin then there is every likelihood that it would do this

[z4ydi]

It depends on which side is fastest to offer an ip address, if the switching links are faster for admin then there is every likelihood that it would do this

To eliminate the doubt and check whether the Admin PCs will pickup a Curriculum IP or not, I disabled the Admin scope and then logged in to an admin PC which is on an admin switch, I have released the IP and forced it to renew, but it came up with the message "Limited or no connectivity", I restarted the PC AND flushed, the dns clicked on Repair etc, it still did not pick up any IP. this is getting confusing now, if the network was interlink then the Admin PC should have picked up a curr IP on this occasion because the only Active scope on the server was the curriculum scope. The mixup should bee on both networks not just curriculum don’t you agree?

[SYNACK]

Yes, I think that your next move should be to try and go through the network and figure out exactly how it is setup and how it is supposed to work as for this to be happening there sounds like there are elements of your network which you do not know about (or have not posted) that are interfering.