This chapter explains how to configure DHCP failover associations. It contains the following sections:
- About DHCP Failover
- Configuring Failover Associations
- Managing Failover Associations
About DHCP Failover
You can create a failover association between two DHCP servers (a primary server and a secondary) and assign the failover association to serve an IPv4 DHCP range. When you set up a failover association, you greatly reduce DHCP service downtime if one of your DHCP servers is out of service. You can better manage IP address requests by making two servers available for DHCP services. You can also configure one of the servers to assume full DHCP services when you know the other server may go out of service for a period of time.
You can configure two NIOS appliances, or one appliance and one external server, to form a failover association. The pairing of a primary and secondary server is called a peer association. The failover peers establish a TCP connection for their communication. They share a pool of IP addresses that they allocate to hosts on their networks based on load balancing. Load balancing is a technique to split the address allocation workload evenly across the two DHCP servers. You can assign a DHCP failover association to serve DHCP ranges in a network. A DHCP failover association can serve DHCP ranges that belong to one network view only. It cannot serve ranges in different network views.
Note: When you assign a failover association to serve DHCP ranges and networks, NIOS denies dynamic BOOTP clients by default, regardless of whether you select or deselect the Deny BOOTP Requests option from Grid Manager. However, if the DHCP ranges or networks are assigned to a single DHCP server (not a failover association), NIOS does not automatically deny dynamic BOOTP clients. In this case, you must manually select the Deny BOOTP Requests option through Grid Manager to ensure that NIOS denies BOOTP requests to avoid problems such as receiving two IP addresses for the same network device. For information about how to deny BOOTP requests, see Configuring IPv4 BOOTP and PXE Properties.
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