Solaris 10 as a DHCP Client

This is kind of an old post, but it still comes up in search results, so I'm going to add to it.

First: having two DHCP servers in a subnet is not going to cause problems no matter what, that's a very misleading statement. What will cause issues is two DHCP servers which are offering the same pool of addresses. You can have two servers offering different ranges of IP addresses (like 192.168.1.1-100 on one and .101-200 on a second) within the same subnet without causing any issues at all. In fact, if you want to have redundant DHCP in your network, this is a recommended/best practice way to do it.

Second, here's some instructions from Microsoft which may get someone a little closer if they happen to have a similar issue: http://technet.microsoft.com/en-us/library/ee405264(v=ws.10).aspx

This is probably not the best way to solve this problem but it worked. Here's what I did.

1) I added the following restriction to my Debian-based DHCP server and removed all of the fixed-address entries. This forces any clients in those IP ranges to move somewhere into the .41 - .199 range, otherwise when I turn on the Windows Server clients will receive leases with IPs in the .11 - .40 range that are already present on the network. I then let things sit long enough for any leases in that IP range to expire and have a new one issued.

subnet 192.168.61.0 netmask 255.255.255.0 {

        option routers 192.168.61.1;
        option subnet-mask 255.255.255.0;
        option broadcast-address 192.168.61.255;

        pool {
                range 192.168.61.0 192.168.61.40;
                deny all clients;
        }
        pool {
                range 192.168.61.41 192.168.61.199;

        }
}

I could not figure out a way to make the Windows Server DHCP implementation act as "authoritative"; the behavior I wanted is when clients with leases from the old Debian-based DHCP server sent their DHCPINFORM packets to the new Windows Server, I wanted those clients to receive a DHCPNAK and the go through the whole process again to get a lease, thus "re-populating" the addressing space from .11 and up.... regardless, continuing on.

2) I cheated by expanding the Exclusion range on the new Windows DHCP server to include 192.168.61.100 - 192.168.61.199. This will force any clients who were assigned an IP in that range by the Debian-based DHCP serve to have their DHCPINFORM denied and then issued a new lease at the "bottom" of the addressing space (.11 and greater).

3) At this point I simply turned the Debian DHCP server off, and the Windows Server on and let the expiry time sort things out. Because of the "deny all clients" line in my dhcpd.conf, there were no clients with "old leases" in the .11 - .40 addressing space that could cause an IP conflict, and because of the Exclusion of .100 - .199 ranges all DHCPINFORM requests were denied (at least I imagine that's what happened... I didn't bother looking at the transaction using a packet sniffer... I probably should of) and the addressing space was re-populated starting from the lower bound of .11.