Nortel SMC 2450, Implementation Manual

Page: 178 / 262

Page 178 of 260 Maintenance
553-3001-225 Standard 1.00 May 2006
enabling the backup virtual routers to confirm that it is down before going on
to the next step:
• If ARP replies from the active master are not received, failover occurs.
• If ARP replies from the active master are received, no failover occurs.
Note: If VRRP multicast advertisement packets are not received on any
backup router, the reason might be that the traffic on the active master is
too heavy for it to send advertisement packets within the advertisement
interval. If you believe this is the case, increase the advertisement
interval value.
When a virtual router comes up from the fault state, it sends ARP requests for
an active master. If the virtual router receives an ARP response, the virtual
router assumes the role of backup. The backup continues sending ARP
messages to the virtual router until it does not receive a response and then
initiates the failover process.
VRRP failover based on links
Link failures decrement the internal priority value that VRRP maintains for
both SMCs. A link failure is defined as a loss of link at the VRRP interface.
At initialization, VRRP sets the priority value to 100 for both SMCs. When a
physical link fails, VRRP reduces the priority value for that SMC by two. If
that causes the SMC’s priority value to fall below that of the other SMC,
failover occurs.
When the link is restored, the priority value for that SMC is increased by two.
This may cause both SMCs to have the same priority values. Nevertheless,
the cluster status does not change until a link failure occurs on the backup and
this causes VRRP to reduce its priority value by two and trigger a failover.
MAC address mapping
The active master uses its virtual router ID (vrid) to set a unique virtual router
MAC address according to this formula: 0x00005E0001<vrid>. This is the
address that the active master returns in response to end-host ARP requests
and proxy ARP requests. Gratuitous ARP (GARP) messages also contain the
active master’s virtual router MAC address. Meanwhile, the backup retains
its physical MAC address.