Introduction
The Virtual Router Redundancy Protocol (VRRP) is a virtual router comprised a Master router and a number of Backup routers. The Master router is responsible for forwarding packets between the hosts and the remote network. It is also responsible for informing the Backup routers of its presence. Should the Master router fail and the presence notifications are not received, the Backup routers will send an advertisement packet. The Master role is taken over by the router with the highest priority, based on the priority received in the advertisement packet. The new Master takes over all the responsibilities of the original Master. By default, when a router becomes available that has a higher priority than the current Master, this router takes over as Master. This is referred to as preempt mode and can be set on or off. When preempt mode is off, once a Backup router becomes the new Master, it will not select a newer Master with a higher priority when it becomes available. Even with preempt mode off, the original router that owns the IP address and priority 255 will always becomes the Master when available.
- VRRP for IPv4 is disabled by default.
- Once you have defined a virtual router session, you must enable VRRP to make the session operational for a given interface.
- The routers priority is a value from 1 to 255, with a default of 100.
- The value 255 is reserved for the router that owns the virtual router’s IP address.
- Preempt mode should be the same for all routers in the virtual router session.
Note: Preempt is on (true) with no delay-time by default. You only need to set preempt mode to true if this has been set to false, or if a delay time is required. Examples
To set the preempt mode for VRRP 1 "on"
awplus# configure terminal
awplus(config)# router vrrp 1 VLAN2
awplus(config-router)# preempt-mode true
awplus(config-router)#exit
To set the preempt delay-time to 30 seconds on VRRP1
awplus# configure terminal
awplus(config)# router vrrp 1 VLAN2
awplus(config-router)# preempt-mode true delay-time 30
awplus(config-router)#exit
To set the preempt mode for VRRP 1 "off"
awplus# configure terminal
awplus(config)# router vrrp 1 VLAN2
awplus(config-router)# preempt-mode false
awplus(config-router)#exit