15.1.8 Group switching function

(1) Overview

A IPv4 virtual router can be grouped together as a unique additional feature of the Switch. You can switch between master and backup for each group. A group consists of a primary virtual router and a follower virtual router. Grouping allows you to use up to 1023 virtual routers. The following figure shows the configuration and switching of the group switching function.

Figure 15-13: Grouping virtual routers

1. A failure is detected by the monitoring function of the master unit and the backup unit.

2. On the master device, all virtual routers in the group that detected the failure transition to backup

3. In the backup device, all virtual routers in the group that detected the failure change to master.

Role of a virtual router	Interface on which the virtual router is configured	Virtual router ID	Virtual router name	Name of the primary virtual router to follow
Primary virtual router	VLAN 100	70	VRRPNAME	-
Follow virtual router 1	VLAN 200	70	-	VRRPNAME
Follow virtual router 2	VLAN 300	70	-	VRRPNAME

(2) Primary virtual router

A virtual router that sends and receives ADVERTISEMENT packets and performs tracking linkage, and switches between master and backup is called a primary virtual router. The state of the primary virtual router determines the state of all virtual routers in the group.

(3) Follower virtual router

A virtual router that determines its state according to the state of the primary virtual router is called a follower virtual router. The follower virtual router does not detect or change the status of the primary virtual router by sending or receiving ADVERTISEMENT packets or by tracking linkage. If the primary virtual router is not running, it is in the initial state. Also, you cannot follow the state of a follower virtual router that includes yourself. The follower virtual router follows the state of the primary virtual router, so it cannot be the address owner.

The following table describes the features that differ from the primary virtual router of the follower virtual router.

Table 15-5: Functions of follower virtual routers

Different function from the primary virtual router	Operation
Switching between master and backup	The status of the primary virtual router is used instead of failure detection/status transitions due to ADVERTISEMENT packettransmission/reception or tracking linkage.
Configuration settings	The following configuration commands used to select a master are invalid. vrrp authentication vrrp preempt vrrp preempt delay vrrp timers non-preempt-swap vrrp priority vrrp track
Operation log	Operation logs associated with state transitions are not output. If the primary virtual router that comprises the group is not set, a log indicating that the follower virtual router is invalid is output to remind you. Also, when the primary virtual router is configured, a recovery message is output.
Get MIB info	This command is not supported. Only the primary virtual router can be acquired.
Sending SNMP Notifications	This command is not supported. Only the primary virtual router is sent.

(4) MAC Learning frame

A virtual router in master status must have its downstream LAN switch learn the virtual MAC addressing.

• Primary virtual router

  The primary virtual router sends ADVERTISEMENT packets. The downstream LAN switch learns the virtual MAC by receiving it.

• Follower virtual router

  The follower virtual router does not send ADVERTISEMENT packets. Instead, it periodically sends MAC Learning frames with the source MAC address as the virtual MAC address. Downstream LAN learns the virtual MAC by receiving this MAC Learning frame.

(5) Notes

1. The virtual router configuration must be the same between the devices that make up the virtual router. For example, if a virtual router is used as the primary virtual router on one switch and as the follower virtual router on the other switch, the virtual router does not operate correctly.

2. Configure the primary virtual router so that it can detect all failures of the follower virtual routers that belong to the group. If the tracking function of the primary virtual router cannot detect a failure, the follower virtual router cannot communicate without a state transition in the event of a failure.

   For example, if the communication paths for ADVERTISEMENT packets differ between the primary virtual router and the follower virtual router, or if VLAN that require monitoring differ, the primary virtual router must monitor all of them.

3. MAC Learning frames are sent every two minutes per follower virtual router. For downstream LAN switches, if the aging time of MAC address table is set to 2 minutes or less, aging and MAC address learning are repeated. It is recommended to set the aging time to 4 minutes or more.