Users Guide

Virtual Router Redundancy Protocol
VRRP allows you to form virtual routers from groups of physical routers on your local area network (LAN). These virtual routing platforms
— master and backup pairs — provide redundancy in case of hardware failure. VRRP also allows you to easily congure a virtual router as
the default gateway to all your hosts and avoids the single point of failure of a physical router.
VRRP:
• Provides a virtual default routing platform
• Provides load balancing
• Supports multiple logical IP subnets on a single LAN segment
• Enables simple trac routing without the single point of failure of a static default route
• Avoids issues with dynamic routing and discovery protocols
• Takes over a failed default router:
– Within a few seconds
– With a minimum of VRRP trac
– Without any interaction from hosts
NOTE: The default behavior of VRRP is active-active. If you want to use VRRP groups on VLANs and do not want the VRRP
backup gateway to forward trac on behalf of the active VRRP gateway in a non-VLT setup, disable the VRRP active-active
feature using the no vrrp mode active-active command.
Conguration
VRRP species a master, or active, router that owns the next-hop IP and MAC address for end stations on a LAN. The master router is
chosen from the virtual routers by an election process and forwards packets sent to the next-hop IP address. If the master router fails,
VRRP begins the election process to choose a new master router which continues routing trac.
VRRP packets transmit with the virtual router MAC address as the source MAC address. The virtual router MAC address associated with a
virtual router is in 00:00:5E:00:01:{VRID} format for IPv4 and 00:00:5E:00:02:{VRID} format for IPv6. The VRID is the virtual router
identier that allows up to 255 IPv4 and IPv6 VRRP routers on a network. The rst four octets are unquenchable, the last two octets are
01:{VRID} for IPv4 and 02:{VRID} for IPv6. The nal octet changes depending on the VRRP virtual router identier.
Basic VRRP Conguration
Layer 3
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