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What is Preempt Preempt forces the system to change the primary router if another router with a higher priority comes online. By default Preempt is enabled in OS10 (Both VRRP Version 2 and VRRP Version 3). Behavior with Preemption Enabled 1. If a higher VRRP Priority switch comes up. Preemption causes that switch to become the primary. 2. If both switches have the same priority and if the current primary goes down. The current backup becomes the primary switch. When the original primary comes up it will be the new backup. 3. If the priority is the same, a change in the IP address to a higher IP on the backup switch will not cause the current primary to become the backup switch. 4. If the priority is the same, a change in the IP address to a higher IP in the current primary causes a reelection, and it becomes the backup switch. 5. If the priority is the same, adding a new switch will not cause the current primary to become the backup switch. 6. If we are using VRRP in VLT nodes, we can use both VLT nodes as active-active (enabled by default.). In Active-Active mode both the VLT nodes of a domain always continue to forward data plane traffic. Configuration Command Parameter OS10#configure terminal Enter into switch configuration mode OS10(config)# interface Enter Interface information (Vlan id, ethernet, portchannel ). OS10(conf-if-XXXXXX)# vrrp-group X Configure VRRP group identification number OS10(conf-if-XXXXXX)# preempt Enable Preempt (By Default Enabled). OS10(conf-if-XXXXXX)# no preempt Disable Preempt
Sample Configuration OS10# configure terminal OS10(config)# interface vlan 1 OS10(conf-if-vl-1)# ip address 10.0.0.1/24 OS10(conf-if-vl-1)# vrrp-group 1 OS10(conf-vlan1-vrid-1)# virtual-address 10.0.0.254 OS10(conf-vlan1-vrid-1)# no preempt
Verify Preempt State 1> Preempt Enabled OS10(conf-if-vl-1)# do show vrrp brief Interface Group Priority Preempt State Version Primary addr(s) Virtual addr --------------------------------------------------------------------------------------------------------------------- vlan1 IPv4 1 100 true primary-state 2 10.0.0.2 10.0.0.254 2>Preempt Disabled OS10(conf-vlan1-vrid-1)# do show vrrp brief Interface Group Priority Preempt State Version Primary addr(s) Virtual addr --------------------------------------------------------------------------------------------------------------------- vlan1 IPv4 1 100 false primary-state 2 10.0.0.2 10.0.0.254
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