In a high-availability network topology, no device can create a single point-of-failure for the network or
force a single point-of-failure to any other part of the network. This means that your network will remain in
service despite the failure of any single device. To achieve this usually requires redundancy for all vital
VRRP enables redundant router configurations within a LAN, providing alternate router paths for a host to
eliminate single points-of-failure within a network. Each participating VRRP-capable routing device is
configured with the same virtual router IP address and ID number. One of the virtual routers is elected as
the master, based on a number of priority criteria, and assumes control of the shared virtual router IP
address. If the master fails, one of the backup virtual routers will take control of the virtual router IP
address and actively process traffic addressed to it.
With VRRP, Virtual Interface Routers (VIR) allows two VRRP routers to share an IP interface across the
routers. VIRs provide a single Destination IP (DIP) for upstream routers to reach various servers, and
provide a virtual default Gateway for the server blades.
Each physical router running VRRP is known as a VRRP router.
Two or more VRRP routers can be configured to form a virtual router (RFC 2338). Each VRRP router may
participate in one or more virtual routers. Each virtual router consists of a user-configured virtual router
identifier (VRID) and an IP address.
Virtual router MAC address
The VRID is used to build the virtual router MAC Address. The five highest-order octets of the virtual router
MAC Address are the standard MAC prefix (00-00-5E-00-01) defined in RFC 2338. The VRID is used to
form the lowest-order octet.
Owners and renters
Only one of the VRRP routers in a virtual router may be configured as the IP address owner. This router
has the virtual router's IP address as its real interface address. This router responds to packets addressed
to the virtual router's IP address for ICMP pings, TCP connections, and so on.
There is no requirement for any VRRP router to be the IP address owner. Most VRRP installations choose
not to implement an IP address owner. For the purposes of this chapter, VRRP routers that are not the IP
address owner are called renters.