Handbook

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VRRP overview
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 (SPOF) 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 network components.
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.
VRRP components
Each physical router running VRRP is known as a VRRP router.
Virtual 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 5 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.
Master and backup virtual router
Within each virtual router, one VRRP router is selected to be the virtual router master. See ―Selecting the
Master VRRP Router‖ for an explanation of the selection process.
NOTE: If the IP address owner is available, it will always become the virtual router master.
The virtual router master forwards packets sent to the virtual router. It also responds to Address Resolution
Protocol (ARP) requests sent to the virtual router's IP address. Finally, the virtual router master sends out
periodic advertisements to let other VRRP routers know it is alive and its priority.
Within a virtual router, the VRRP routers not selected to be the master are known as virtual router backups.
Should the virtual router master fail, one of the virtual router backups becomes the master and assumes
its responsibilities.
Virtual Interface Router
At Layer 3, a Virtual Interface Router (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 destination
networks, and provide a virtual default Gateway.