Reference Guide

● 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
Configuration
VRRP specifies a master (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 are transmitted with the virtual router MAC address as the source MAC address. The virtual router MAC address
associated with a virtual router is in format: 00:00:5E:00:01:{VRID} for IPv4 and 00:00:5E:00:02:{VRID} for IPv6. The VRID is
the virtual router identifier that allows up to 255 IPv4 VRRP routers and 255 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 and allows for up to 255 VRRP routers on a network.
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 the master router (Router A) becomes unavailable, Router B (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. Router B receives and forwards packets on interface ethernet 1/1/5. Until
Router A resumes operation, VRRP allows Router B to provide uninterrupted service to the users on the LAN segment accessing
the Internet.
Create virtual router
VRRP uses the VRID to identify each virtual router configured. Before using VRRP, you must configure the interface with the
primary IP address and enable it.
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