Multiple Registration Protocol

Generic Attribute Registration Protocol, is a VLAN management protocol, for trunking between multilayer switches.

The IEEE 802.1d standard mentions the idea of dynamic registration of 'group membership' between MAC bridges.

In recent times, multilayer switches, which primarily combine OSI Layer 2 and Layer 3 functionality, can use GARP to dynamically manage VLAN registration.

the IEEE 802.1d standard is available in PDF format here