The High Availability Protocol used on the Kemp Loadmaster is CARP. CARP works in the same way as Cisco’s VRRP. It uses multicast address 188.8.131.52. In order for CARP to work between a pair of Loadmasters, both Loadmasters need to be on the same broadcast domain.
During normal production the setting for this feature should be "No Preferred Host". We only recommend specifying a host during the testing of HA failover. Setting this to prefer a specific host in production may lead to unexpected failbacks leading to further outages.
Virtual MAC is a means of doing HA at layer 2, rather than layer 3. Essentially, in addition to a shared IP there is a shared MAC address which is owned by whichever unit is active. By implementing this, all virtual service traffic will communicate to this shared MAC address, allowing the standby device to pick up the traffic seamlessly. In the event of a failover, upstream devices do not need to change the ARP record associated with services.
You can select the interface to send and receive inter-HA traffic from within the WUI:
In addition to the shared management IP, each LoadMaster can be managed directly. This individual web interface allows certain local management tasks, but does not allow the configuration of services. For full configuration options, be sure you are connecting the shared address of the HA pair.
Ideally, HA Checks should be set for every interface that will be in use for production traffic. This includes, but is not limited to the interfaces that are used to pass traffic for virtual services, server pools and default gateway traffic. HA Checks can also be included on management interfaces, but be aware that LoadMaster will become standby in the event that this network goes down.
Upgrading to a high availability pair may be easier than you would think. It is recommended that you first create a backup of your LoadMaster configuration and potentially create a certificate backup if you had imported any certificates to your LoadMaster. Once you have received licensing for your second LoadMaster, navigate to the WUI of your single LoadMaster. Please note that as this procedure requires reboots.
The real time status of a HA pair can be obtained by examining the two colored indicators on the header of your WUI display. The first square is the HA1 appliance and the second square is the indicator for the HA2 appliance. When correctly configured the two indicators should be colored green. This should be true for all WUI's (HA Shared IP, HA1, and HA2).
At least three free IP addresses are needed to set up a HA-pair.
The HA Virtual ID can be found in System Configuration > Miscellaneous Options > HA Parameters > HA Virtual ID
Under the WUI, on your single unit that is already configured:
This option determines the amount of time it will take before failover will occur to your Standby unit when your Master becomes unavailable. Timeout values to choose from are 3s, 6s, 9s, 12s and 15s. The recommended (default) value is 9 seconds. To select the option in the WUI:
This option is used to select a preferred HA unit. This option can be set to either HA1, HA2 or No preferred host (default).