System Failover

System Failover

Failover Flow

The system failover is switching to a passive system when an active system is in a state of failure(e.g. hardware fault, network problem).

A passive system synchronizes all data from the master database in which is running in an active system by the Database Replication and monitors the active system.

A passive system sends a heartbeat about every 10 seconds to an active system. If the passive does not receive a response from an active system for the Deadtime, the passive system switches the mode to "active".

This system failover enables continuous service and you can connect the management page without changing the URI because a virtual IP is automatically configured in an active system by the failover service.

The failover service in an active system listens on UDP port 6010 to receive a heartbeat from a passive system.

All services in the active and passive devices work as shown in the table below.

Service	Active System	Passive System
dhcpv4	running	running
dhcpv6	running	running
radius	running	running
logexp	running	running but only saves its Syslog.
failover	Configuring a Virtual IP	Monitoring an active system and replicating the database
Database	Master	Slave

Note that, If an active system is recovered from a fault after another system has switched to the active mode, the recovered system switches to passive mode. In other words, The failback does not occur. You can configure the System Failover via the CLI.

System Failover Switch-Over

The following table shows you when a system switches its mode. Several case numbers indicate a Switch-Over condition and you can see them while monitoring the logs of the failover service. Note that you need to enable the "runtime log" for the failover service to display logs.

Init mode	Peer Response	Current mode(switched mode)	Case Number
active	no-response	active	C7
	zero(initializing)	active	C1, C5
	passive	active	C5
	active	passive	C4
passive	no-response	active	C6
	zero(initializing)	passive	C1, C3
	passive	active	C4
	active	passive	C5

System Failover Case Numbers

Case Number	Description
C1	If DEVICE#1 is in an initialization state, and it gets a response from DEVICE#2 that is also initializing, DEVICE#1 switches its mode to the Initial Mode configured.
C2	If DEVICE#1 is in an initialization state, and it gets a response from DEVICE#2 that is in either an "active" or "passive" state, DEVICE#1 switches to the opposite mode from DEVICE#2.
C3	If DEVICE#1 is in a "passive" state, and it gets a response from DEVICE#2 that is initializing, DEVICE#1 keeps its current state.
C4	If DEVICE#1 is in either an "active" or "passive" state, and it gets a response from DEVICE#2 that is in the same state as it is, DEVICE#1 switches to the opposite mode from DEVICE#2. Typically this case rarely occurs but it can occur because of the misconfiguring of the system failover(e.g. configuring the same initial mode to both devices).
C5	If DEVICE#1 is in either an "active" or "passive" state, and it gets a response from DEVICE#2 that is in the opposite state as it is, DEVICE#1 keeps its current state.
C6	If DEVICE#1 is in an initialization state, the initial mode is "passive", and it does not get a response from DEVICE#2, DEVICE#1 tries again to connect to DEVICE#2 without switching its mode. If DEVICE#2 does not respond during the INIT-DEADTIME(30 seconds), DEVICE#1 switches its mode to "active".
C7	If DEVICE#1 is in an initialization state, the initial mode is "active", and it does not get a response from DEVICE#2, DEVICE#1 switches its mode to "active".
C8	If DEVICE#1 is in a "passive" state, and it does not get a response from DEVICE#2, DEVICE#1 tries again to connect to DEVICE#2 without switching its mode. If DEVICE#2 does not respond during the deadtime configured, DEVICE#1 switches its mode to "active".
C9	It shows you DEVICE#1 is in an "active" state and it does not get a response from DEVICE#2. This case never occurs.
C10	If DEVICE#1
C11	AAA
C12	AAA
C13	AAA