DHCP leases from old box to new box.

I am replacing old DHCP servers that are end of life with some new
servers.

Every machine I support uses a telnet like application - so I can't
just switch IP addresses on the clients. Doing so drops their
sessions, thus loosing their work.

Is it true that to move the leases all I need to do is copy the
dhcpd.leases file from the old server to the new server, shut down the
old DHCPD and start up the new one? (Of course, the new server is
configured like the old.)

 

DHCP servers look at the MAC address when assigning IP addresses. A new
computer, with a new NIC, will have a new MAC address. Incidentally, if
it's necessary to have consistent addresses, map DHCP addresses to MACs.
This way, specified IPs will be permanently assigned to the specific
computers.

 

So you recommend my DHCP server use DHCP client and use reservations to
assign the DHCP servers their settings?

No no no.

My DHCP servers have static IP settings. I'd never have my DHCP
servers get their IP settings from DHCP.

Doesn't really address the question, however after much digging it
looks like that's all I have to do. Move the old leases file from the
old DHCP server to the new DHCP server, making sure neither are up at
the same moment.

 

I did this and it did work just fine. Though it seems as if my NT 4
clients wouldn't renew if the new server had a different IP. Not 100%
positive, but I got "Unable to renew lease" doing ipconfig /renew when
I had the leases on the server but hadn't changed it's IP address yet.

 

:I did this and it did work just fine. Though it seems as if my NT 4
:clients wouldn't renew if the new server had a different IP. Not 100%
ositive, but I got "Unable to renew lease" doing ipconfig /renew when
:I had the leases on the server but hadn't changed it's IP address yet.

One of the options typically supplied in the lease is the IP address of
the issuing server (dhcp-server-identifier). A client would first try
to renew from that server before resorting to DHCPDISCOVER to locate a
new server.