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Chapter 32 IPv6 VRRPv3 Configuration
32.1 Introduction to VRRPv3
VRRPv3 is a virtual router redundancy protocol for IPv6. It is designed based on VRRP
(VRRPv2) in IPv4 environment. The following is a brief introduction to it.
In a network based on TCP/IP protocol, in order to guarantee the communication between the
devices which are not physically connected, routers should be specified. At present there are
two most commonly used methods to specify routers: one is to study dynamically via routing
protocols (such as internal routing protocols RIP and OSPF); the other is to configure statically.
Running dynamical routing protocol on each terminal is unrealistic, since most operating
systems for client end do not support dynamical routing protocol, even if they do, they are
limited by the overheads of management, convergence, security and many other problems. So
the common method is to adopt static routing configuration on terminal IP devices, which
usually means specify one or more default gateway for terminal devices. Static routing
simplifies the management of network and reduces the communication overheads of terminal
devices, but it still has a disadvantage: if the router acting as the default gateway breaks, the
communication of all the hosts which use this gateway as their next hop host. Even if there are
more than one default gateways, before rebooting the terminal devices, they can not switch to
the new gateway. Adopting virtual router redundancy protocol (VRPR) can effectively avoid the
flaws of statically specifying gateways.
In VRRP protocol, there are two groups of import concepts: VRRP routers and virtual routers,
master routers and backup routers. VRRP routers are routers running VRRP, which are
physical entities; virtual routers are the ones created by VRRP, which are logical concepts. A
group of VRRP routers cooperate to comprise a virtual router, which acts outwardly as a logical
router with a unique fixed IP address and MAC address. The routers belonging to the same
VRRP group play two mutually exclusive roles at the same time: master routers and backup
routers. One VRRP group can only have one master router other but one or more backup
routers. VRRPv3 protocol uses selection policy to select a master router from the router group
to take charge of responding ND(Neighbor Discovery) neighbor request messages(ARP in
IPv4) and forwarding IP data packets, while the other routers in the group will be in a state of
waiting as backups. When the master router has a problem for some season, the backup
router will be updated to the master router after a delay of a few seconds. Since this switch is
very fast and does not need to change IP address or MAC address, it will be transparent to
terminal user systems.
In IPv6 environment, the hosts in a LAN usually learn the default gateway via neighbor
discovery protocol (NDP), which is implemented based on regularly receiving advertisement
messages from routers. The NDP of IPv6 has a mechanism called Neighbor Unreachability