XGS-5240-Series User Manual

Configuration Guide of XGS-5240-Series
61-1
Chapter 61 IPv6 VRRPv3 Configuration
61.1 Introduction to VRRPv3
VRRPv3 is a virtual router redundancy protocol for IPv6. It is designed based on V
RRP (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 b
etween 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); th
e 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 routi
ng protocol, even if they do, they are limited by the overheads of management, conver
gence, security and many other problems. So the common method is to adopt static ro
uting configuration on terminal IP devices, which usually means specify one or more de
fault gateway for terminal devices. Static routing simplifies the management of network
and reduces the communication overheads of terminal devices, but it still has a disadva
ntage: 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 f
laws of statically specifying gateways.
In VRRP protocol, there are two groups of import concepts: VRRP routers and virt
ual routers, master routers and backup routers. VRRP routers are routers running VRR
P, 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. T
he 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 p
olicy 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 upd
ated 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 te