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High Availability for DHCP

Owned by Sri Raghu
Last updated: Sept 06, 2024
3 min read


Two NIOS-X Servers can be added to an HA (High Availability) group. In case one NIOS-X Server is down, the second NIOS-X Server can take over DHCP lease management without causing downtime. High Availability can be configured as Active/Active, Active/Passive, Advanced Active/Passive, or Anycast with the following benefits:

  • Active/Active: Node 1 and Node 2 are both active and constantly keep their databases synchronized. When one node is down, the workload is completely taken over by the other node. When the node is back online, it takes control of the leases that it owned before it went down. For example, on High Availability, see Configuring High Availability. For more information about High Availability vs. DHCP failover, see Kea High Availability vs ISC DHCP Failover. The address pools do not rebalance, so it is recommended to create larger pools with fewer clients. 
  • Active/Passive: Only Node 1 manages the leases for all clients. Node 1 syncs with Node 2 to keep the database synced. If Node 1 is down, Node 2 takes over managing the leases. A node can only belong to one HA group. 
  • Advanced Active/Passive (Hub-and-Spoke): Advanced Active/Passive allows you to include a single node to multiple HA groups. Only Node 1 manages the leases for all clients. Node 1 syncs with Node 2 to keep the database synced. If Node 1 is down, Node 2 takes over managing the leases. A node can perform different roles in different HA groups. A node can be active in one or more HA groups, passive in one or more HA groups, or service leases individually while being part of an HA group. 
  • Anycast: Universal DDI now supports the ability to configure HA groups that utilize the BloxOne Anycast service. A DHCP Anycast HA group is an Active/Active pair of NIOS-X Servers that share a virtual IP address (VIP) for DHCP protocol communications, acting from the clients’ perspective, as “one” DHCP server.  The VIP is advertised using the BloxOne Anycast service, which leverages either OSPFv2, OSPFv3, or BGP to announce reachability. For more information, see Creating Anycast Configuration. Node 1 and Node 2 are both active and constantly keep their databases synchronized. When Node 1 is down, the workload is completely taken over by Node 2. When Node 1 is back online, it takes control of the leases that it owned before it went down. 

Before configuring High Availability over anycast, see Configuring Anycast for more information. 

Active/Active

In Active-Active mode, Node 1 and Node 2 are both active and constantly keep their databases synchronized. When one node is down, the workload is completely taken over by the other node. When the node is back online, it takes control of the leases that it owned before it went down.

Active/Passive 

In Active-Passive mode, only Node 1 manages the leases for all clients. Node 1 syncs with Node 2 to keep the database synced. If Node 1 is down, Node 2 takes over managing the leases. A node can only belong to one HA group.

Advanced Active/Passive (Hub-and-Spoke)

Advanced Active-Passive (Hub-and-Spoke) mode allows you to include a single node to multiple HA groups. Only Node 1 manages the leases for all clients. Node 1 syncs with Node 2 to keep the database synced. If Node 1 is down, Node 2 takes over managing the leases. A node can perform different roles in different HA groups. A node can be active in one or more HA groups, passive in one or more HA groups, or service leases individually while being part of an HA group.

Anycast

A DHCP Anycast HA group is an Active-Active pair of hosts that share a virtual IP address for DHCP protocol communications, acting from the perspective of a client as one DHCP server. The virtual IP address is advertised using the BloxOne Anycast service, which leverages OSPFv2, OSPFv3, or BGP to announce reachability. Nodes 1 and 2 are both active and constantly keep their databases synchronized. When Node 1 is down, the workload is completely taken over by Node 2. When Node 1 is back online, it takes control of the leases that it owned before it went down.

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