3Com Switch 4800G 24-Port Configuration Manual page 1074

1074 C 87: VRRP C
HAPTER
VRRP Standby Group
Overview
ONFIGURATION
Apparently, this approach to enabling hosts on a network to communicate with
external networks is easy to configure but it imposes a very high requirement of
performance stability on the device acting as the gateway. A common way to
improve system reliability is to use more egress gateways, introducing the problem
of routing among the multiple egresses.
Virtual Router Redundancy Protocol (VRRP) is an error-tolerant protocol designed
to address this problem through separating physical devices from logical devices.
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 device fails and prevent network interruption due to a single
link failure.
There are two VRRP versions: VRRPv2 and VRRPv3. VRRPv2 is based on IPv4, while
VRRPv3 is based on IPv6. The two versions implement the same functions but
provide different commands.
VRRP combines a group of switches (including a master and multiple backups) on
a LAN into a virtual router called standby group.
The VRRP standby group has the following features:
A virtual router has an IP address. A host on the LAN only needs to know the IP
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address of the virtual router and uses the IP address as the next hop of the
default route.
Every host on the LAN communicates with external networks through the
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virtual router.
Switches in the standby group elect the gateway according to their priorities.
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Once the master switch acting as the gateway fails, the other switches in the
standby group elect a new gateway to undertake the responsibility of the failed
switch, thus ensuring that the hosts in the network segment can communicate
with the external networks uninterruptedly.
Figure 319 Network diagram for VRRP
Host A
Host B
Host C
Virtual router
Switch A
Switch B
Network
Switch C