Virtual Router Overview - 3Com 5500-EI PWR Install Manual

Preemptive mode and preemption delay of a switch in a VRRP group
You can configure a 5500-EI Ethernet switch to operate in preemptive mode.
In non-preemptive mode, as long as a switch in a VRRP group becomes the master, it stays as the
master as long as it operates normally, even if a backup is assigned a higher priority later.
If all the switches in a VRRP group are set to operate in preemptive mode, a backup sends VRRP
advertisements when it finds that its priority is higher than that of the current master. In this case a
new election of master is triggered, and the backup becomes the master and the former master
becomes a backup accordingly.
You can also set the preemption delay for a 5500-EI switch.
Setting a delay period aims at:
In an unstable network, backups in a VRRP group possibly cannot receive VRRP advertisements
from the master in time due to network congestions. In this case, the backup considers itself as the
master and sends out VRRP advertisements to elect master. This causes the master of the VRRP
group to be determined frequently.
With preemption delay configured, if a backup does not receive VRRP advertisements from the
master in time, it waits for a while before switching to a new master. The backup does not send
VRRP advertisements if it receives VRRP advertisements from the master during the specified
delay period.
Authentication type and authentication key of a switch in a VRRP group
VRRP provides the following authentication types:
simple: Simple text authentication. In a network under possible security threat, the authentication
type can be set to simple. With the simple authentication type configured, the switch adds an
authentication key into a VRRP packet before transmitting it. The receiver then compares the
authentication key of the packet with the locally configured one. If they are the same, the packet will
be taken as a true and legal one. Otherwise it will be regarded illegal and discarded.
md5: MD5 authentication. In a vulnerable network, the authentication type can be set to md5. The
switch then uses the authentication type provided in the Authentication Header and the local MD5
algorithm to authenticate the VRRP packets. Packets that fail to pass the authentication are
discarded. The switch then sends trap messages to the NMS.

Virtual Router Overview

VRRP group and virtual router IP address configuration
To create a VRRP group, you need to configure an IP address for the VRRP group virtual router. The
VRRP group is automatically created after you configure the first IP address for the VRRP group virtual
router. Other IP addresses configured for the virtual router after this one are just added to the IP address
list of the virtual router.
The virtual router IP address has the following features:
The IP address of the virtual router can be an unassigned IP address in the network segment
where a member switch of the VRRP group resides.
You can specify the virtual router IP address as the IP address used by a member switch in the
VRRP group. In this case, the member switch is called an IP address owner.
1-3