[TriLUG] Windows DHCP to ISC DHCP migration

[Kevin Flanagan]

I'd vote for the second option, stand up the new DHCP servers, and have them
start handing out addresses.  If you have a lot of reservations then you
will need to work on getting that out of the Windows servers, but I'd expect
that it can be done.

Lance is right, the DHCP server is who decides the lease length, the client
takes the lease, and checks back in 1/2 of the lease time to see if it can
keep the address.  I believe that ours are set for 60 minutes at work.


Kevin



On 10/24/07, Lance A. Brown <lance at bearcircle.net> wrote:
>
> 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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