I have two DHCP servers working with split scopes [1] for redundancy. I also have a fairly long delay set on the backup server's scopes (250 milliseconds). It appears one server or another will get odd leases depending on which server's DHCP offer it accepted.
An example lease has these values:
Client IP: 10.192.9.1
Name: 10.192.9.1
Lease Expiration: Infinite
Type: DHCP/BOOTP
Unique ID: 31302E3139322E392E3100
These will be hidden from view unless I "reconcile" the scope. Nothing actually exists at that IPv4 address; it doesn't answer ICMP and there's no ARP table entry for it at the switch. The lease is counted when I display statistics for the scope whether visible or not.
It turns out the unique ID is the hexadecimal representation of the lease's IPv4 address in ASCII (10.192.9.1) with a trailing 0x00 character, which is usually used as a C/C++ end-of-string indicator for ASCII or ANSI strings.
Prior to using Server 2012 DHCP servers on this network, the two 2008R2 domain controllers had DHCP running on them in a similar fashion and I haven't seen this behavior before. I wanted to set up 2012 DHCP to use Failover, but that didn't work out [1].
I can purge these things routinely I suppose, but I can see this problem filling up a scope rather quickly and breaking DHCP for that subnet. They won't expire because the scopes have infinite lease durations. I'd script a scheduled sweep for them,
but they will be hidden unless I reconcile the scopes first, which I guess I could script too [2]. But that seems like an ugly workaround. Is there a better fix for this?
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[1] The clients don't like DHCP failover because they need infinite leases, and the maximum client lead time setting causes them to get 24-hour-long leases at first, then get infinite leases upon renewal twelve hours later, but that's another story. The vendor that makes the devices in question really, really want me to use infinite leases. I think it's to cover up a bug they have in their IPv4 stack related to DHCP renewals or something.
[2] Except Windows Server 2012 PowerShell doesn't support the Repair-DhcpServerv4IpRecord cmdlet. I'd have to upgrade to 2012R2 for that.