You want to implement router redundancy in the Company network using the best method
available. Which protocol specified by RFC 2281 provides network redundancy for IP
networks, ensuring that user traffic immediately and transparently recovers from first-hop
failures in network edge devices or access circuits?

A.
ICMP

B.
IRDP

C.
HSRP

D.
STP

E.
None of the other alternatives apply

Explanation:
HSRP is a Cisco-proprietary protocol developed to allow several routers (or multilayer
switches) to appear as a single gateway address. RFC 2281 describes this protocol in more
detail. Basically, each of the routers that provides redundancy for a given gateway address
is assigned to a common HSRP group. One router is elected as the primary, or active,
HSRP router, another is elected as the standby HSRP router, and all the others remain in
the listen HSRP state. The routers exchange HSRP hello messages at regular intervals, so
they can remain aware of each other’s existence, as well as that of the active router.
An HSRP group can be assigned an arbitrary group number, from 0 to 255. If you configure
HSRP groups on several VLAN interfaces, it can be handy to make the group number the
same as the VLAN number. However, most Catalyst switches support only up to 16 unique
HSRP group numbers. If you have more than 16 VLANs, you will quickly run out of group
numbers. An alternative is to make the group number the same (that is, 1) for every VLAN
interface. This is perfectly valid because the HSRP groups are only locally significant on an
interface. HSRP Group 1 on interface VLAN 10 is unique from HSRP Group 1 on interface
VLAN 11.