Configuring The Advertisement Interval; Configuring Virtual Router Priority; Setting Preemption For Virtual Routers - Alcatel-Lucent OmniSwitch 6850-48 Network Configuration Manual

VRRP Configuration Overview

Configuring the Advertisement Interval

The advertisement interval is configurable, but all virtual routers with the same VRID must be configured
with the same value. If the advertisement interval is set differently for a master router and a backup router,
VRRP packets may be dropped because the newly configured interval does not match the interval indi-
cated in the packet. The backup router will then take over and send a gratuitous ARP
virtual router IP address and the virtual router MAC address. In addition to creating duplicate IP/MAC
address messages, both routers will begin forwarding packets sent to the virtual router MAC address. This
will result in forwarding duplicate packets.
To avoid duplicate addresses and packets, make sure the advertisement interval is configured the same on
both the master and the backup router.
For more information about VRRP and ARP requests, see
To configure the advertisement interval, use the
-> vrrp 6 4 disable
-> vrrp 6 4 interval 5
In this example, virtual router 6 is disabled. (If you are modifying an existing virtual router, the virtual
router must be disabled before it may be modified.) The vrrp command is then used to set the advertising
interval for virtual router 6 to 5 seconds.

Configuring Virtual Router Priority

VRRP functions with one master virtual router and at least one backup virtual router. A priority value
determines the role each router plays. It also decides the selection of backup routers for taking over as the
master router, if the master router is unavailable.
Priority values range from 1 to 254. The default priority value is 100. If a VRRP router owns the IP
address of the virtual router and the IP address of the physical interface, this router will function as a
virtual router master and its priority value will be 255. The value cannot be set to 255 if the router is not
the IP address owner.
If there is more than one backup router, it is necessary to configure their priorities with different values.
This is done so to elect the backup router with the highest value as the master. If the priority values are the
same, the backup virtual router with the highest physical interface IP address is chosen as the master.
To set the priority, use the
-> vrrp 6 4 disable
-> vrrp 6 4 priority 50
In this example, virtual router 6 is disabled. (If you are modifying an existing virtual router, it must be
disabled before it is modified.) The virtual router priority is then set to 50. Since the default priority is 100,
setting the value to 50 provides the router with lower priority in the VRRP network.

Setting Preemption for Virtual Routers

When a master virtual router becomes unavailable (goes down for whatever reason), a backup router will
take over. When there is more than one backup router and if their priority values are very nearly equal, the
skew time may not be sufficient to overcome delays caused by network traffic loads. This may cause a
lower priority backup to assume control before a higher priority backup. But when the preempt mode is
enabled, the higher priority backup router will detect this and assume control.
page 32-12
vrrp
vrrp command with the priority keyword and the desired value. For example:
OmniSwitch AOS Release 6 Network Configuration Guide
"ARP Requests" on page
command with the interval keyword. For example:
Configuring VRRP
which includes the
,
32-8.
September 2009