DHCP Server question

[karkclent]

Hi all,

We have 2 remote sites. Site A is connected to Site B via leased T1 line. Site A provides DHCP services to Site B over the WAN. Site A also provides Internet and Email services.

In a month, we will sever the link to Site A (companies are splitting into 2 entities). We want to install DHCP services on Site B. However, we would like this to be a smooth transition. We cannot do a hard cutover because there will be an interim period where clients still require access to some services at Site A. My question is, how do we do this so that we can bring up our DHCP server ahead of time? My plan was to copy the DHCP scope from Site A's server and put it on Site B's new server. I would then create the existing active leases as "active reservations" to avoid any conflicts. As the active leases timed out, the clients would pick up a new IP from the new DHCP server.

Does anyone see any flaws in my logic? Any suggestions would appreciated.

TIA,
kc

 

[OzDog]

karkclent,

At the moment, I assume Site B would be on a different scope to Site A.

Do the IPs of Site B need to stay exactly the same? If not, I would create a new scope at Site B with the same range of addresses and subnet masks etc, then activate it and have someone at site A de-activate the Site A scope at the same time.

As clients try to renew they will find that the original is unavailable and re-broadcast for a new address. They will request the same address as they have, and they should get it - bear in mind it's not guaranteed.

If the addresses need to stay the same, you can add the reservations prior to activating/deactivating the scopes.

Hope this helps.
Cheers,
Sam

 

[karkclent]

Thanks for the reply, Sam.

Technically, the addresses don't have to stay strictly the same. But the IP pool will be identical (the IP scheme is staying the same). Having said that, how do I guarantee that new clients won't be given IPs already in use by clients of the old scope? By your solution, if I de-activate scope A and activate scope B (with identical parameters), how does B know which IPs are currently in use? Wouldn't this cause conflicts for new clients?

 

[seanos]

Karkclent

Not sure on this one, but when you activate scope B, and A is still running, scope B will have no active connections. Once the line to scope A is cut, the client machines will rebroadcast, and attempt to reconnect to Scope B, once they've found it, using the same address.
Scope B should (in theory) just accept these connections as they will be using address that are not in use. (as far as B is concerened)

hope this makes sense.

Seanos
.........
Member of the 'Linux is better than Windows Guild'.

 

[OzDog]

Your are correct - there is no guarantee. The PC's will request their old addresses (that's just the way DHCP works), but they are not guaranteed to get it.

What you can do is stop the DHCP Server service on Scope A, copy it's database, start the service, then put the database onto Server B and start it. At this time you can stop Scope B on server A, and the reservations etc should be there.
Cheers,
Sam