HSRP is a protocol developed by Cisco that enables several routers on a LAN to work together to provide a phantom router IP and MAC address for workstations to use as a default gateway. If the active HSRP router goes down, a standby HSRP router takes over and becomes the active router. This ensures that the workstations alway have a default gateway to communicate with.
VRRP is the rest of the internetworking industry's standardized version of a protocol that does basically the same thing as Cisco's HSRP. The advantage to VRRP is that it can be used to provide redundancy between different vendors' equipment.
At one point, Cisco claimed that VRRP infringed on the HSRP patent. But it would seem that point of contention no longer exists, since VRRP is still available. It is even showing up in some Cisco products, although that is the result of company acquisitions. It is not due to deliberate efforts by Cisco to be interoperable with other vendors.
Here's some insight into the technical details of the two protocols.
RFC2281: Cisco Hot Standby Router Protocol (HSRP)
http://www.ietf.org/rfc/rfc2281.txt
RFC2338: Virtual Router Redundancy Protocol
http://www.ietf.org/rfc/rfc2338.txt
And here's a summary of the key difference between the two:
"The key difference between VRRP and HSRP, and Digital's scheme, is authentication. HSRP has a password field, including a default value, which translates to "cisco," for the installation of parameters, but there is no other form of security. Security is critical because it provides a useful function and the IESG is now insisting that all new protocols include appropriate security mechanisms."
http://www.ietf.org/proceedings/97aug/transit97aug-97.htm
Hope this helps.
