17.2. Configuring VRRP

17.2. Configuring VRRP
	Chapter 17. VRRP

VRRP operates within a layer 2 broadcast domain, so VRRP configuration on the FB2900 comes under the scope of an interface definition. As such, to set-up your FB2900 to participate in a Virtual Router group, you need to create a vrrp object, as a child object of the interface that is in the layer 2 domain where the VRRP operates.

17.2.1. Advertisement Interval

A master indicates that it still 'alive' by periodically sending an advertisement multicast packet to the group members. A failure to receive a multicast packet from the master router for a period longer than three times the advertisement interval timer causes the backup routers to assume that the master router is down.

The interval is specified in multiples of 10ms, so a value of 100 represents one second. The default value, if not specified, is one second. If you set lower than one second then VRRP3 is used by default (see below). VRRP2 only does whole seconds, and must have the same interval for all devices. VRRP3 can have different intervals on different devices, but typically you would set them all the same.

The shorter the advertisement interval, the shorter the 'black hole' period, but there will be more (multicast) traffic in the network.

Note

For IPv6 VRRP3 is used by default, whereas for IPv4 VRRP2 is used by default. Devices have to be using the same version. IPv4 and IPv6 can co-exist with one using VRRP2 and the other VRRP3. Setting the same config (apart from priority) on all devices ensures they have the same version.

17.2.2. Priority

Each device is assigned a priority, which determines which device becomes the master, and which devices remain as backups. The (working) device with the highest priority becomes the master.

If using the real IP of the master, then the master should have priority 255. Otherwise pick priorities from 1 to 254. It is usually sensible to space these out, e.g. using 100 and 200.

A VRRP setting can have a profile. Unlike most profiles, if the profile is off then VRRP continues to work, but works with a priority forced to a low priority (usually 1, but can be configured). This means the VRRP will be backup but this depends on the setting for low-priority and what priority other devices are set to.