Which protocol will enable a group of routers to form a single virtual router and will use the real IP
address of a router as the gateway address?

A.
Proxy ARP

B.
HSRP

C.
IRDP

D.
VRRP

E.
GLBP

Explanation:
The correct answer is VRRP whereby either a virtual or physical address can be chosen as the
gateway address. If the physical address of R2 is the gateway address, then R2 will become the
gateway. If R2 goes down, R3 (or R4 etc) will become the gateway and will assume the IP
address which, to it, will be a virtual one as none of its interfaces are configured with that address.
In this scenario, R2, R3 and R4 form one virtual router whereby R1’s physical address is used as
the gateway address. HSRP does not use physical addresses for the gateway at all.

Reference: Virtual Router Redundancy Protocol
(http://www.cisco.com/en/US/docs/ios/12_0st/12_0st18/feature/guide/st_vrrpx.html)