The All-New Switch Book: The Complete Guide to LAN Switching Technology, Second Edition

10.3. GARP Multicast Registration Protocol

GARP Multicast Registration Protocol (GMRP) is the industry-standard protocol that incorporates all of the concepts discussed in section 10.2.1. The name of the protocol itself has an interesting story.

When the IEEE task force first defined the protocol, it was called the Group Address Registration Protocol, with the acronym GARP. As the name implied, it provided for explicit registration of multicast addresses across the catenet. During the development of IEEE 802.1p, a second project was started to work on Virtual LANs (VLANs), ultimately creating the IEEE 802.1Q standard. During the work on IEEE 802.1Q, it was recognized that an equivalent protocol was needed for declaration and registration of VLAN membership. Rather than design two completely independent protocols, a Generic Attribute Registration Protocol (also abbreviated GARP) was devised; this general-purpose protocol could be used to register multicast addresses, VLANs, and any other connectivity or membership-style information. Thus, the meaning of the GARP acronym changed from being a multicast-specific protocol to being a generic protocol.^[] The multicast registration protocol became GMRP, and the VLAN registration protocol became GVRP. (If you can't figure out what GVRP stands for, you will have to wait until Chapter 12, "Virtual LANs: The IEEE Standard.")

^[] A similar acronym-transformation occurred in Rich's neighborhood. He lives in a very rural, mountainous area in Northern ...