Users Guide

VRRP:
● Provides a virtual default routing platform
● Provides load balancing
● Supports multiple logical IP subnets on a single LAN segment
● Enables simple traffic 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 traffic
○ Without any interaction from hosts
NOTE: The default behavior of VRRP is active-active. If you do not want the VRRP backup gateway to forward traffic on
behalf of the active VRRP gateway in a non-VLT setup, use the no vrrp mode active-active command disable the
VRRP active-active feature.
Configuration
VRRP specifies 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 traffic.
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 identifier that allows up to 255 IPv4 and IPv6 VRRP routers on a network. The first four octets are
unquenchable, the last two octets are 01:{VRID} for IPv4 and 02:{VRID} for IPv6. The final octet changes depending on the
VRRP virtual router identifier.
Basic VRRP Configuration
The example shows a typical network configuration using VRRP. Instead of configuring the hosts on network 10.10.10.0 with the
IP address of either Router A or Router B as the default router, the default router of all hosts is set to the IP address of the
virtual router. When any host on the LAN segment requests Internet access, it sends packets to the IP address of the virtual
router.
Router A is configured as the master router with the virtual router IP address and sends any packets addressed to the virtual
router to the Internet. Router B is the backup router and is also configured with the virtual router IP address.
If Router A, the master router, becomes unavailable (the connection between the LAN segment and Router A on ethernet 1/1/6
goes down), Router B, the backup router, automatically becomes the master router and responds to packets sent to the virtual
IP address. All workstations continue to use the IP address of the virtual router to transmit packets destined to the Internet.
Layer 3
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