DHCP in a Multi-Subnet Environment

If you don't create superscope DHCP will assign IP address from the first scope and then from the next scope if ip addresses reach its limit in the first scope. Superscope takes care of this. When a client request an IP address the Superscope will give the correct IP address from correct superscope.

Thankx

Mtstewdog, what kind of network gear do you have?  Usually, all your VLANs have to be explicitly configured to pass DHCP requests from the local network over to where the DHCP server is.  Cisco does it with "ip helper".

dhcp works with lease times
after 50% of the time has elapsed, the client will request a renewal, if no response, it will wait until 75% and try again, and if no response, cut the remaining time in half and so on

Thanks for all the suggestions.  Due to the physical location of each subnet, it will take me some time to determine if I've made progress based on you suggestions.

Thanks again, Stew

Ok :-)
Thankx

> Mtstewdog, what kind of network gear do you have?  Usually, all your VLANs have to be explicitly configured to pass DHCP
> requests from the local network over to where the DHCP server is.  Cisco does it with "ip helper".

That's *one* way to do it.  Another is for the DHCP server to have a NIC on each VLAN, or a trunked port.  A third possibility is to have a separate DHCP server on each VLAN -- I don't think that could produce this problem.  I don't think we've been told which approach is used on his network.

I *assume* that after moving to a new VLAN, he does an "ipconfig /release" and "ipconfig /renew" to get a new lease.  But maybe he's not, and if so that's the problem.

I thank you for all the great suggestions and tips, but alas, I've made no progress.  It has occurred to me, however, that perhaps some additional information on my behalf may help.

Each of my subnets are behind separate Cisco routers which themselves are separated by point-to-point T1 circuits.

When I move to a new location/subnet/LAN, not only must I perform an ip config /release and /renew, but I also must actually go into the Windows Server 2003 DHCP snap-in and delete the old lease from the previous location.  Now I can do the /release/renew and DHCP will assign a proper IP address.

Thanks again!

Stew

Wow!

Wow?  What does that mean?

Perhaps I should have added that it is my desire to NOT have to have users bother with /release/renew.  I want them to seamlessly, transparently, move from one location to another and have DHCP handle the details.

My Cisco expert tells me that as a last resort, he can set up the routers to handle the necessary DHCP tasks.  But having DHCP in my domain controller is clearly better, more centralized way to go.

Stew

How many machine move between subnets?
If not many, you could use user calsses for those machines, and set the lease time short on those (short lease times mean more chatter)
so they will have to renew a lot sooner than the machines that don't move
http://www.winnetmag.com/Articles/Print.cfm?Action=Print&ArticleID=7983
you may have to setup dual dhcp servers (seperate the scope of course)
and then set the mobile machines with a very short lease time

So, if all the subnets are seperated by Cisco routers which are seperated by T1's ... it doesn't sound as if people are moving from one floor/subnet to another.  They probably move from one geographic location to another, right?  If so, they probably shut down their machine.  So, if they shut down their machine and go to another office and start it up, DHCP client would request an address and it would all work seamlessly.

With Cisco routers, use "ip helper" to handle the DHCP requests passing the layer 3 boundry.

:)

I don't think it should be delete/refund.  I think the points should be split.

Why should the points be split?  Between who?  Gee whiz, I still have the problem.  Why should points be awarded in such a case?

Every suggestion offered is one I've been trying to avoid.  Sure, I could have a separate DHCP server at each location.  And sure, I could use my Cisco routers to do the DHCP.  All of these would solve the problem but does not address the orginal challenge presented.  I asked if my current DHCP server could be configured to handle the case of a machine (typically a laptop) moving from location to location without having to force the user to do an ipconfig /release and /renew and so far, nobody has offered anything that works -- or at least said, "Nope.  Can't be done".

Thanks for your consideration,

Stewart

I'm sorry Stewart - I thought the question had been abandoned - as did the administrators here - since there was no reply to my last post.

I was saying are your locations geographically seperate - so the likelihood is that someone will visit two spots and start up their machine at a different spot?  If so, then if your routers hand off the DHCP request to the centralized server it should work as you desire.  When the request comes in from some subnet, it gets assigned an address out of the scope you define for that subnet.

Okay, perhaps we can try this again...

Yes, I have five separate locations, specifically five Ace Hardware stores.  All five locations are connected by point-to-point T1 circuits.  There is a Cisco router at each location  Our main location has a pair of Citrix servers as well as a third server acting as a domain controller and DHCP server.

I have set up DHCP (Windows Server 2003 Standard Edition) with five separate scopes.  All five of these are pretty much set up identically, except that the third octet is different depending on the location as follows:

Store #1: 10.0.1.x
Store #2: 10.0.2.x
Store #3: 10.0.3.x
Store #4: 10.0.4.x
Store #5: 10.0.5.x

Allow me to further state exactly how DHCP is set up because perhaps that will provide a clue as to what may need to be done.

First, we have the address Pool.  For each location, it's 10.0.X.102 to 10.0.X.240 (addresses below 102 are used by some devices with static IP addresses)

Under Scope Options, again, they are all configured identically, with the exception that the router is specific to the scope.  In other words, for Scope number 1 (store number 1) the router is 10.0.1.254, for scope number two (store number 2), the router is 10.0.2.254, scope 3 - 10.0.3.254, scope 4 - 10.0.4.254 and scope 5 - 10.0.5.254.

All DHCP requests and leases are functioning properly, EXCEPT for that case when a laptop moves from one location to another.  In such a case, the laptop will be assigned it's original IP address.  For example, I plug my laptop into the LAN at store 1 and it's assigned 10.0.1.138.  Now I move to store 2 and plug in.  I will once again be assigned 10.0.1.138.  Of course, with that 3rd octet being a "1" while I'm at location 2 (10.0.2.xxx), it won't work!  Performing an ipconfig /release /renew will remedy the situation, but I want to avoid forcing my less techno-savvy users to do this sort of thing.

I have tried changing the lease time and it doesn't seem to make any difference.

Appreciate any ideas and would LOVE to find a solution and give up the points!

Thanks,

Stew

Dear pseudocyber,

You'd think that a very short lease (one that will obviously expire) would do the trick.  Alas, it does not.  It seems that the lease still appear, but is labeled as "expired".  Whatever, it is defnitely causing the newly located laptop to be assigned the original (and wrong for this location!) IP address.  Sure, I can go into DHCP and delete the lease, but again, that's the sort of thing that I wish to avoid.

My main point here is that I really thought (being the eternal optimist that I am) that DHCP in Windows Server 2003 SURELY could handle a simple challenge such as this.  SURELY!  After all, what I'm trying to accomplish certainly does not seem (at least not to me) to be such and uncommon scenario.  Quite the contrary, actually.

HOWEVER, I must admit, pseudocyber, that your suggestion to use ipconfig /release - ipconfig /renew, but by way of creating a desktop shortcut is simple and effective.  Funny how sometimes the simplest solutions are the most elusive.  I think that suggestions is the best I've heard so far.  While not what I was hoping for, it will get the job done.  Therefore, I feel it's proper for you to get the points.  WELL DONE!

Stew