3Com S7906E - Switch, Configuration Manual

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Configuring a default route for network hosts facilitates your configuration, but also requires high
performance stability of the device acting as the gateway. Using more egress gateways is a common
way to improve system reliability, introducing the problem of routing among the multiple egresses.
Virtual Router Redundancy Protocol (VRRP) is designed to address this problem. VRRP adds a group
of routers that can act as network gateways to a VRRP group, which forms a virtual router. Routers in
the VRRP group elect a master through the VRRP election mechanism to take the responsibility of a
gateway, and hosts on a LAN only need to configure the virtual router as their default network gateway.
VRRP is an error-tolerant protocol, which improves the network reliability and simplifies configurations
on hosts. Deploying VRRP on multicast and broadcast LANs such as Ethernet, you can ensure that the
system can still provide highly reliable default links without changing configurations (such as dynamic
routing protocols, route discovery protocols) when a router fails, and prevent network interruption due to
failure of a single link.
VRRP works in one of the following two modes:
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Standard protocol mode: Includes two versions based on RFCs: VRRPv2 and VRRPv3. VRRPv2
is based on IPv4, and VRRPv3 is based on IPv6. The two versions implement the same functions
but are applied in different network environments. Refer to VRRP Standard Protocol Mode for
details.
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Load balancing mode: Extends the standard protocol mode and realizes load balancing. Refer to
VRRP Load Balancing Mode for details.
VRRP Standard Protocol Mode
Introduction to VRRP Group
VRRP combines a group of routers (including a master and multiple backups) on a LAN into a virtual
router called VRRP group.
A VRRP group has the following features:
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A virtual router has a virtual IP address. A host on the LAN only needs to know the IP address of the
virtual router and uses the IP address as the next hop of the default route.
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Every host on the LAN communicates with external networks through the virtual router.
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Routers in the VRRP group elect the master acting as the gateway according to their priorities. The
other routers function as the backups. When the master fails, to ensure that the hosts in the
network segment can communicate with the external networks uninterruptedly, the backups in the
VRRP group elect a new gateway to undertake the responsibility of the failed master.