[TriLUG] Windows DHCP to ISC DHCP migration

Lance A. Brown lance at bearcircle.net
Wed Oct 24 21:06:18 EDT 2007


Joseph Mack NA3T said the following on 10/24/2007 6:00 PM:
> You don't get a lot of choice with lease time. Windows 
> machines only ask for 5mins, even if you allow a longer 
> lease time. Linux machines ask for an hour. I suspect a 
> windows dhcpd will only grant a 5 min lease. So the 
> changeover has to occur in a time less than 
> 5mins/number_clients.

I *know* this is wrong.  I've seen windows DHCP server providing much
longer leases than just 5 minutes.  Lease durations are specified by the
server, not the client.

5 minute lease times would create a lot unnecessary extra network traffic.

You *can* extract the current lease information from a windows DHCP server:

>Q: How can we get a list of all active leases in a text file for a
>given DHCP server?
>A: Go to the Address leases of each scope in the DHCP snap-in and dump
>the leases to a text file from the DHCP server snap-in.

You should be able to massage the output from that into a usable leases
file for your linux DHCP server.

Alternatively, configure the new linux server with the reservations
you've already set up, then just turn off the Windows DHCP server at any
point, and turn on the Linux server.  The DHCP client machines will
figure things out for themselves.

--[Lance]

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