The multicast address 224.0.1.39 is used by AutoRP for RPAnnounce messages, which are sent by each candidate rendezvous point (RP) to advertise its eligibility to become an RP. The RPAnnounce messages are received by the mapping agent, which maps the candidate RPs to multicast groups. If multiple routers are advertised as candidate RPs for a multicast group, the router with the highest IP address is used as the RP for that group.

The multicast address 224.0.1.40 is used by AutoRP for RPDiscovery messages, which are sent by mapping agents to advertise the authoritative RP for a multicast group. AutoRP dynamically determines the RP for a multicast group so that RPs need not be manually configured. AutoRP uses a mapping agent to learn which routers are advertised as candidate RPs for each multicast group. The candidate list is then advertised to client routers.

The multicast address 224.0.0.2 is the allrouters address. This address is used by Protocol Independent Multicast version 1 (PIMv1) to send status messages, such as querymessages. The all routers address is also used by Internet Group Management Protocol (IGMP) and Hot Standby Router Protocol (HSRP).

The multicast address 224.0.0.13 is the allPIMrouters address. This address is used by PIMv2 to send status messages, such as hello messages, prune messages, and assert messages. The allPIMrouters address is also used by the Bootstrap Router (BSR) feature to dynamically assign RPs to multicast groups. Other PIMv2 message types include the Register message, the RegisterStop message, and the Join/Prune message.

The multicast address 224.0.0.102 is used for Gateway Load Balancing Protocol (GLBP) hello messages. GLBP is a Ciscoproprietary protocol that was developed to resolve some of the shortcomings of other router redundancy protocols, such as HSRP and Virtual Router Redundancy Protocol (VRRP). By default, hello messages are sent among GLBP group members every three seconds.