H3C Technologies H3C S3600 Series Switches - Manual (Page 576)

1-2
The networking illustrated in Figure 1-1 requires high stability of the default gateway. Normally, adding
egress gateways is used to improve the system reliability. In this case, how to route between multiple
egresses needs to be solved.
Virtual Router Redundancy Protocol (VRRP), an error-tolerant protocol defined in RFC 2338, well
solves the problem mentioned above through separating physical devices and logical devices. In LANs
with multicast or broadcast capabilities (such as Ethernet), VRRP can avoid single point failure through
establishing backup links without modifying the configuration of dynamic routing protocols and router
discovery protocols.
Introduction to VRRP Group
VRRP allows you to combine a group of LAN switches (including a master and several backups) into a
VRRP group. The VRRP group functions as a virtual router, forwarding packets as a gateway.
Figure 1-2 VRRP network diagram
Host 1
Ethernet
Master
Network
Host 2 Host 3
Backup
10.100.10.7/24 10.100.10.9/24 10.100.10.8/24
Actual IP address
10.100.10.2/24
Actual IP address
10.100.10.3/24
Virtual IP address
10.100.10.1/24
Virtual IP address
10.100.10.1/24
As shown in Figure 1-2 , a VRRP group has the following features:
z The virtual router (the VRRP group) has its own IP address (10.100.10.1 in the above figure).
z The switches within the VRRP group must have their own IP addresses (such as 10.100.10.2 for
the master and 10.100.10.3 for the backup).
z Hosts in the LAN use the IP address of the virtual router (that is, 10.100.10.1) as their default
gateway.
z Hosts in the LAN only know the IP address of this virtual router, that is, 10.100.10.1, but not the
specific IP addresses 10.100.10.2 of the master and 10.100.10.3 of the backup.
If the master in the VRRP group goes down, the backups in the VRRP group will reelect a master by
priority. The backup with the highest priority functions as the new master to guarantee normal
communication between the hosts and the external networks.
Priority of a switch in a VRRP group
You can configure the priority of a switch in a VRRP group. A master is elected from these
VRRP-enabled switches by priority and the remaining switches are backups. The master in a VRRP
group is the one currently with the highest priority.
Switch priority ranges from 0 to 255 (a larger number indicates a higher switch priority). Note that only 1
through 254 are available to users. Switch priorities 0 and 255 are reserved for special uses and the IP
address owner respectively.