DHCP clustering
NxFilter already supports clustering, and we can extend this capability to provide a fail-safe mechanism for the DHCP service as well.
To find out more about NxFilter clustering, read Clustering with NxFilter
How it works
NxFilter includes a built-in clustering feature. We can leverage this existing structure to build DHCP redundancy.
When you configure DHCP through the GUI on a NxFilter cluster, the master node will operate as the primary DHCP server.
You can then designate one of the slave nodes as a backup DHCP server.
If the master node goes down, the backup DHCP server will automatically take over DHCP responsibilities until the master is restored.
Split scope
Implementing DHCP clustering is more delicate than other clustering features. Unlike general data replication,
DHCP deals with real-time IP address assignment, and incorrect configurations can lead to IP address collisions in the network.
To avoid this, NxFilter's DHCP clustering uses a split-scope model.
For example, suppose your network uses the 192.168.0.0/24 subnet:
- The primary DHCP server (on the master node) could be assigned the range: 192.168.0.2 ~ 192.168.0.100
- The backup DHCP server (on a slave node) could be assigned a non-overlapping range: 192.168.0.101 ~ 192.168.0.200
This setup prevents overlapping address assignments, even in case of temporary overlap due to failover detection delay.
GUI setup
You can configure a secondary (backup) DHCP server through the NxFilter GUI.
When you set a secondary DHCP server in the GUI:
- listen_ip
The slave node IP address on which the secondary DHCP server listens.
- start_ip / end_ip
The range of IP addresses to be assigned.
Make sure the IP range does not overlap with the primary DHCP server's range.
Manual setup
The backup server works in the same way as the primary server.
You can copy the dhcp.properties file from the master node to the target slave node.
After that, adjust the following parameters:
- listen_ip
The IP address the DHCP server listens on.
- start_ip / end_ip
The range of IP addresses to be assigned.
- secondary_flag
Set this property to '1' to enable backup (secondary) mode on this node.
- no_synch_setup
Set this property to 1 to prevent the configuration file from being synchronized from the primary server.
The prevent_conflict option is ignored in clustering mode, because one of the DHCP servers must always
be running for uninterrupted service.