The HSRP is an FHRP
designed to allow for transparent failover of the first-hop IP device. HSRP
provides high network availability by providing first-hop routing redundancy
for IP hosts on Ethernet configured with a default gateway IP address. HSRP is
used in a group of devices for selecting an active device and a standby device.
In a group of device interfaces, the active device is the device of choice for
routing packets; the standby device is the device that takes over when the
active device fails or when preset conditions are met.
IPv6 hosts learn of
available IPv6 devices through IPv6 neighbor discovery RA messages. These are
multicast periodically, or may be solicited by hosts. HSRP is designed to
provide only a virtual first hop for IPv6 hosts.
An HSRP IPv6 group
has a virtual MAC address that is derived from the HSRP group number, and a
virtual IPv6 link-local address that is, by default, derived from the HSRP
virtual MAC address. Periodic RAs are sent for the HSRP virtual IPv6 link-local
address when the HSRP group is active. These RAs stop after a final RA is sent
when the group leaves the active state.
Periodic RAs for
the interface link-local address stop after a final RA is sent while at least
one virtual IPv6 link-local address is configured on the interface. No
restrictions occur for the interface IPv6 link-local address other than that
mentioned for the RAs. Other protocols continue to receive and send packets to
HSRP uses a
priority mechanism to determine which HSRP configured device is to be the
default active device. To configure a device as the active device, you assign
it a priority that is higher than the priority of all the other HSRP-configured
devices. The default priority is 100, so if you configure just one device to
have a higher priority, that device will be the default active device.