3Com Switch 7750 Configuration Guide

VRRP Overview 555
■ The virtual router IP address and the IP addresses used by the member switches
in a backup group must belong to the same network segment. If not, the
backup group will be in the initial state (the state before you configure the
VRRP on the switches of the group). In this case, VRRP does not take effect.
■ A backup group is removed if all its virtual router IP addresses are removed. In
this case, all the configurations performed for the backup group get ruined.
According to the standard VRRP, an attempt to ping the IP address of a virtual
router will result in failure. Thus, you cannot locate the network fault by using the
ping command.
To solve this problem, you can enable the switches in a backup group to respond
the ping operations destined for the virtual router IP addresses.
Mapping Virtual IP Addresses to MAC Addresses
A Switch 7750 provides the following functions in addition to forwarding data
correctly.
■ You can map multiple virtual IP addresses of the backup group to a virtual MAC
address as needed. You can also map virtual IP addresses to the MAC address
of a switch routing interface.
■ You need to map the IP addresses of the backup group to the MAC addresses
before enabling VRRP feature on a Switch 7750. If VRRP is already enabled, the
system does not support this configuration.
By default, virtual router IP addresses are mapped to the virtual MAC address of a
backup group.
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When you map a virtual IP address to the virtual MAC address on a Switch 7750,
the number of backup groups that can be configured on a VLAN interface is
determined by the chips used. Refer to device specification for detail.
Backup Group
Configuration Tasks
Configuring switch priority
You can configure the priority of a switch in a backup group. VRRP will determine
the status of each switch in a backup group according to the priority of the switch.
The master switch in a backup group is the one currently with the highest priority.
Switch priority ranges from 0 to 255 (a larger number indicates a higher switch
priority) and defaults to 100. Note that only 1 through 254 are available to users.
Switch priority of 255 is reserved for IP address owners.
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The priority of the IP address owner is fixed to 255.
Configuring preemptive mode for a switch in a backup group
As long as a switch in the backup group becomes the master switch, other
switches, even if they are configured with a higher priority later, do not preempt
the master switch unless they operate in preemptive mode. The switch operating
in preemptive mode will become the master switch when it finds its priority is
higher than that of the current master switch, and the former master switch
becomes a backup switch accordingly.