|  | 6.3 | LMI Features
| 6.3.2 | Multicasting and inverse ARP
Multicasting is another valuable optional LMI feature. Multicast groups are designated by a series of four reserved DLCI values (1019 to 1022). Frames sent by a device using one of these reserved DLCIs are replicated by the network and sent to all exit points in the designated set. The multicasting extension also defines LMI messages that notify user devices of the addition, deletion, and presence of multicast groups. In networks that take advantage of dynamic routing, routing information must be exchanged among many routers. Routing messages can be sent efficiently by using frames with a multicast DLCI. This allows messages to be sent to specific groups of routers. The Inverse ARP mechanism allows the router to automatically build the Frame Relay map, as shown in the Figure. The router learns the DLCIs that are in use from the switch during the initial LMI exchange. The router then sends an Inverse ARP request to each DLCI for each protocol configured on the interface if the protocol is supported. The return information from the Inverse ARP is then used to build the Frame Relay map.