VRRP overview
In many networks, edge devices are often configured to send packets to a statically configured default router. If
this router becomes unavailable, the devices that use it as their first-hop router become isolated from the network.
Virtual Router Redundancy Protocol (VRRP) uses dynamic failover to ensure the availability of an end node's
default router. This is done by assigning the IP address used as the default route to a "virtual router" or VR. The
VR includes:
• An owner router assigned to forward traffic designated for the virtual router (If the owner is forwarding traffic for
the VR, it is the master router for that VR.)
• One or more prioritized backup routers (If a backup is forwarding traffic for the VR, it has replaced the owner
as the master router for that VR.)
This redundancy provides a backup for gateway IP addresses (first-hop routers) so that if a VR's master router
becomes unavailable, the traffic it supports will be transferred to a backup router without major delays or operator
intervention. This operation can eliminate single-point-of-failure problems and provide dynamic failover (and
failback) support. As long as one physical router in a VR configuration is available, the IP addresses assigned to
the VR are always available, and the edge devices can send packets to these IP addresses without interruption.
Advantages to using VRRP include:
• Minimizing failover time and bandwidth overhead if a primary router becomes unavailable.
• Minimizing service disruptions during a failover.
• Providing backup for a load-balanced routing solution.
• Addressing failover problems at the router level instead of on the network edge.
• Avoiding the need to make configuration changes in the end nodes if a gateway router fails.
• Eliminating the need for router discovery protocols to support failover operation.
Both VRRPv2 and VRRPv3 are supported. IPv4 VRs can be configured for both version 2 and version 3. IPv6
VRs can only be configured for version 3.
For more information, see
on page 336.
Configuring VRRP
Enabling VRRP in the global configuration context
VRRP can be configured regardless of the global VRRP configuration status. However, enabling a VR and
running VRRP requires enabling it in the global configuration context.
Syntax:
[no] router vrrp
IPv4|IPv6
enable|disable
Enables or disables VRRP operation in the global configuration context. for IPv4, IP routing must be enabled
before enabling VRRP on the router. For IPv6, IPv6 unicast-routing must be enabled before enabling VRRP on
the router. Disabling global VRRP halts VRRP operation on the router, but does not affect the current VRRP
configuration. Enabling or disabling VRRP generates an Event Log message.
Chapter 16
Virtual Router Redundancy Protocol (VRRP)
Chapter 16 Virtual Router Redundancy Protocol (VRRP)
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