Windows Server 2012

What is DHCP Failover in Windows Server 2012

DHCP failover: Windows Server 2012 allows administrators to configure two DHCP servers (maximum limit) for failover and they will be sharing DHCP lease between them. In case one DHCP server is down, other DHCP server would be serving the clients requests. DHCP scopes are limited to IPv4 only.  Load-balancing can also be configured to distribute client requests between the two servers.

Dynamic Host Configuration Protocol (DHCP) assigns IP addresses automatically to the network clients. Clients would be disconnected from the network if DHCP server is down. Windows Server2008 provides two failover solutions but there were few challenges associated with both of them:-

·         To use DHCP in a Windows failover cluster: Provides failover support in case one DHCP server fails. Challenge: Cluster uses a single shared storage causing single point of failure. Setting up of Clusters involves investment and time.

·         To split DHCP scope: We can split the DHCP scope by using 70-30% rule of thumb. Range of IPs falling in one scope can be divided among two DHCP servers. Primary server would be assigning 70% of the addresses and remaining 30% are assigned to the backup server. The problem in this scenario would be what if primary DHCP falls down and clients would be getting new IPs from backup DHCP server.

Windows Server 2012 has overcome both of these limitations by providing DHCP services all the time and clients could extend their current IP lease even if primary DHCP server is down.

 This can be achieved by configuring DHCP servers and they will be replicating lease information between them. One DHCP server would be assuming the responsibility for servicing the clients when the other server is unavailable. Load-balancing can also be configured to distribute client requests between the two servers.

Windows Server 2012 supports maximum two DHCP servers for failover and is limited to IPv4 scopes and subnets.

Configure DHCP Failover option