Filter
Top Products
Alteon OS Application Guide
226
Chapter 13: High Availability 42C4911, January 2007
VRRP Operation
Only the virtual router master responds to ARP requests. Therefore, the upstream routers only
forward packets destined to the master. The master also responds to ICMP ping requests. The
backup does not forward any traffic, nor does it respond to ARP requests.
If the master is not available, the backup becomes the master and takes over responsibility for
packet forwarding and responding to ARP requests.
Selecting the Master VRRP Router
Each VRRP router is configured with a priority between 1–254. A bidding process determines
which VRRP router is or becomes the master—the VRRP router with the highest priority.
The master periodically sends advertisements to an IP multicast address. As long as the back-
ups receive these advertisements, they remain in the backup state. If a backup does not receive
an advertisement for three advertisement intervals, it initiates a bidding process to determine
which VRRP router has the highest priority and takes over as master.
If, at any time, a backup determines that it has higher priority than the current master does, it
can preempt the master and become the master itself, unless configured not to do so. In pre-
emption, the backup assumes the role of master and begins to send its own advertisements. The
current master sees that the backup has higher priority and will stop functioning as the master.
A backup router can stop receiving advertisements for one of two reasons—the master can be
down, or all communications links between the master and the backup can be down. If the
master has failed, it is clearly desirable for the backup (or one of the backups, if there is more
than one) to become the master.
NOTE – If the master is healthy but communication between the master and the backup has failed,
there will then be two masters within the virtual router. To prevent this from happening, config-
ure redundant links to be used between the switches that form a virtual router.