Filter
Top Products
Configuring Router Redundancy
3-187
3
Command Usage
Address Assignment –
• The designated virtual IP address must be configured on at least one router in the
virtual router group. If an IP address is not specified, the designated address is
learned through the exchange of HSRP messages. Note that the designated
address cannot be the same as a physical address.
• The subnet mask for the physical interface on which the designated address is
configured is used as the subnet mask of the designated address. The interfaces
of all routers participating in a virtual router group must be within the same IP
subnet.
• Configuring a new designated address on the current master router will override
the designated address currently is use.
• If multiple secondary addresses are configured on the current VLAN interface,
these addresses can also be supported on the virtual router by selecting the
“Secondary” Virtual IP mode.
• HSRP is enabled once the designated address and priority are configured, and the
master and standby routers are elected based on highest priority. If you need to
customize any of the other parameters for HSRP such as authentication, tracking,
or advertisement interval, then first configure these parameters before enabling
HSRP.
• HSRP creates a virtual MAC address for the master router based on a standard
prefix, with the last octet equal to the group ID. When a backup router takes over
as the master, it continues to forward traffic addressed to this virtual MAC address.
However, the backup router cannot reply to ICMP pings sent to addresses
associated with the virtual group because the IP address owner is off line.
Virtual Router Priority –
• The router with the highest priority is elected as the master virtual router. The router
with the next highest priority is elected as the standby router. The standby router
will become the master router if the current master fails. When the original master
router recovers, it will become the active master router again if the configured
priorities have not been changed.
• If two or more routers are configured with the same HSRP priority, the router with
the higher IP address is elected as the new master router if the current master fails.
• The priority setting takes precedence over authentication. In other words, if a router
with a higher priority than any other router comes on line, but is not configured with
an authentication string, or is configured with the wrong string, it will still take over
as the active master.
• The HSRP priority can change dynamically depending on the availability of a
tracked interface.
Preempting the Master –
• If preempt is enabled, and this router has a priority higher than the current acting
master, it will take over as the new master. If preempt is not enabled, this router
will only take over if it has the highest priority in the group and the current master