What is the Master/Slave role on a VIP?

Short answer

Master/Slave is the role that determines, for a VIP, on which device it will normally run, and that is selected separately for each VIP. The VIP is active on the device where it is Master; the Slave device keeps it in reserve and takes over the VIP when the VRRP advertisements from the Master stop or when the selected TR7 check fails. The role is selected from the Master/Slave column in the IP table when the VIP is added or edited; the default is Master, and it applies to the device logged in to; the peer device automatically takes the opposite role. By giving different VIPs different Master devices, the two devices can carry traffic at the same time. In the list, the VIPs appear with the (M) suffix on the Master side and the (S) suffix on the Slave side.

How Does the Role Work?

	Master	Slave
In the normal state	The VIP is active on this device and receives the traffic	Keeps the VIP in reserve
When the Master fails	-	Takes over the VIP
When the Master comes back	Takes the VIP back	Releases the VIP
Stable state on the Interfaces screen	Master VIP is active	Slave VIP
While the VIP is on the Slave, both devices connected	Master VIP is absent	Slave VIP is active
While the Master device cannot be reached (on the Slave device's screen)	Cluster connection is down	Both VIP might be active

• The role belongs to the VIP: Different VIPs on the same interface can be Master on different devices (IP types in cluster mode). This way, one group of VIPs runs on the first device, the other group on the second device, and both devices carry traffic; when one device fails, all VIPs gather on the other.
• The role is relative to the device logged in to: A VIP selected as Master appears on the peer device with the (S) suffix.
• Prerequisite: A VIP Communication pair must be selected on the interface where the VIP is; without it being selected, the VIP does not become active (VIP Communication).
• Changing the role: The VIP is right-clicked and Master/Slave is changed with Edit IP (Edit IP).
• Moment of transition: If VIP Transition Method = Only VRRP, when the advertisements from the Master stop; in the TR7-checked methods, additionally when the link or gateway check fails on only one device (VIP transition).
• VIP enabled on only one device: If the VIP is turned off for one device with Disable for, it runs fixed on the other device and does not take part in failover (Right-clicking an IP address).

Common Misconceptions

• "Master is the role of a device." The role is separate for each VIP; the same device can be Master on one VIP and Slave on another VIP.
• "The device with Cluster ID 1 is the Master." The Cluster ID only determines who initiates the connection during pairing; it does not determine the VIP role.
• "The Slave device receives no traffic at all." It does not receive traffic on the VIPs where it is Slave; if there are other VIPs where it is Master, it receives their traffic.
• "The role is selected separately on both devices." The role is selected on one device; the peer device takes the opposite role automatically.

How it is done in the documentation

• IP types in cluster mode
• Add IP · IP (Master/Slave)
• Interfaces · The VIP Transition Mechanisms

Related questions

• What is a VIP, and when is it needed?
• How does a cluster work?
• When a failed device comes back, does the VIP automatically move back to it?