Understanding DHCP Failover

The DHCP failover feature allows two DHCP servers to provide IP addresses and option configurations for the same subnet or range. The two DHCP servers exchange lease information. It is also possible to configure failover in a load balancing configuration that distributes client requests to the two servers.

The failover relationship is limited to IPv4 areas and subnets (Figure 3). Computers that use IPv6 determine their own IPv6 address with stateless, automatic IP configuration. In this mode, the DHCP server only provides the DHCP option configuration. The server does not retain lease status information.

Figure 3: IPv4 and IPv6 can be used in parallel on a DHCP server in Windows Server 2016.

A server with the role of a primary server for one subnet can also be a secondary server for another subnet. In a load-balancing mode deployment, the two servers simultaneously process IP addresses and options for clients on a specified subnet. The client requests are processed by load balancing and distributed to the two servers.

For DHCP failover to work, the time between the two servers in a failover relationship must be synchronized. On startup, the failover configuration wizard compares the current time on the servers involved. If the time difference between the servers is greater than one minute, the failover setup process is stopped.

Static Entries in the DNS Database

The DNS servers are administered in Server Manager by calling the DNS command in the Tools menu. There may be situations where you need to add hostnames manually and the dynamic entries alone are not sufficient. In this case, use the New Host command in the context menu of the zone to which the entry is to be added. You enter the hostname – without the name of the zone – and the IP address. You can make an entry in the reverse lookup zone called a PTR record.

Right-clicking on a zone gives you two management options for this zone: Click Reload to reload the settings and the view of the zone in the snap-in, whereby the zone is transferred from AD back into the view. With New Host (A or AAAA) , insert a new static entry into the DNS database as described. The AAAA entry contains an IPv6 address; an A entry contains an IPv4 address.

Conclusions

IPv6 is bound to assert itself on internal networks, but before you switch all servers and network devices to IPv6, you should make sure that all applications on the network support it. Windows Server 2016 also changes the management of network traffic, saying goodbye to some proven tools. IPv6 requires some training but offers some advantages in the network and runs largely automatically once the settings are set correctly.