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Configuring Router Redundancy
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• VRRP creates a virtual MAC address for the master router based on a standard
prefix, with the last octet equal to the group ID. When a backup router takes over
as the master, it continues to forward traffic addressed to this virtual MAC address.
However, the backup router cannot reply to ICMP pings sent to addresses
associated with the virtual group because the IP address owner is off line.
Virtual Router Priority –
• The Owner of the virtual IP address is automatically assigned the highest possible
virtual router priority of 255. The backup router with the highest priority will become
the master router if the current master fails. However, because the priority of the
virtual IP address Owner is the highest, the original master router will always
become the active master router when it recovers.
• If two or more routers are configured with the same VRRP priority, the router with
the higher IP address is elected as the new master router if the current master fails.
Preempting the Acting Master –
• The virtual IP Owner has the highest priority, so no other router can preempt it, and
it will always resume control as the master virtual router when it comes back on
line. The preempt function only allows a backup router to take over from another
backup router that is temporarily acting as the group master. If preemption is
enabled and this router has a higher priority than the current acting master when it
comes on line, it will take over as the acting group master.
• You can add a delay to the preempt function to give additional time to receive an
advertisement message from the current master before taking control. If the router
attempting to become the master has just come on line, this delay also gives it time
to gather information for its routing table before actually preempting the currently
active master router.
Field Attributes (VRRP Group Configuration)
•
VLAN ID
– ID of a VLAN configured with an IP interface. (Range: 1-4093; Default: 1)
• VRID – VRRP group identifier. (Range: 1-255)
• State – VRRP router role. (Values: Master, Backup)
• Virtual Address – Virtual IP address for this group.
• Interval – Interval at which the master virtual router sends advertisements
communicating its state as the master.
• Preemption – Shows if this router is allowed to preempt the acting master.
• Priority – Priority of this router in the VRRP group.
• AuthType – Authentication mode used to verify VRRP packets from other routers.