What is DHCP Failover?

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DHCP Failover is a mechanism whereby two DHCP servers are both configured to manage the same pool of addresses so that they can share the load of assigning leases for that pool, and provide back-up for each other in case of network outages.

Failover partnerships are configured per pool, so one DHCP server may have several active partnerships with different peers.  The configuration elements of DHCP Failover are to establish peering relationship first (via the failover peer declarations in dhcpd.conf), and then to establish which pools will use the partnership by adding the failover peer option to the pool declarations individually.

For more information and a sample configuration, please refer to: A Basic Guide to Configuring DHCP Failover

dhcpd will only accept inbound TCP connections from its configured failover peers

But note that the dialogue between failover partners is neither encrypted nor authenticated.  Since most DHCP servers exist within an organization's own secure Intranet, this would be an unnecessary overhead.  However, if you have DHCP failover peers whose communications traverse insecure networks, then we recommend that you consider the use of VPN tunneling between them to ensure that the failover partnership is immune to disruption (accidental or otherwise) via third parties.  Your local firewalls should also be configured to prevent access to the failover port by unauthorized devices.