Love or hate Microsoft Windows DHCP, chances are there is some amount of it installed in effectively every modern data center. The nice integration with Windows DNS and Active Directory make it a safe bet for providing DHCP access for both clients and servers (that’s another discussion I’m starting soon; stay tuned).
While DHCP is nice and easy to use, we have also become quite dependent on it. Windows Server 8 introduces a new feature to help us mitigate the risk of losing a DHCP Server — DHCP Failover. Simply put, DHCP Failover allows a scope to be sent to a partner server.
This scope attribute can accommodate a failover partner that can work in either a failover (hot standby) or a load-balancing context. This can address many concerns about the availability of a single Windows server holding the DHCP Server role. Figure A shows a DHCP scope with a failover option being presented:
The failover relationship with two DHCP servers is sharing the scope between them. Both servers would be authorized in Active Directory, and there is an additional protection mechanism for the scope to be managed by two servers in the form of a shared secret. The shared secret simply authorizes the two servers to coordinate the scope in the failover mode, and the failover relationship can allow a server to be administratively set to “down” if it is not available. The failover relationship screen is shown in Figure B:
While the DHCP Failover mechanism is not as robust as a failover cluster group resource (also known as a Microsoft Clustering Service resource), it does provide additional availability levels for the DHCP Server role in mission critical environments.
Does the DHCP Failover option appeal to you? How would it fit in your infrastructure? Share your comments below.