RFC 2337 (rfc2337) - Page 2 of 8

Intra-LIS IP multicast among routers over ATM using Sparse Mode PIM

RFC 2337            IP multicast over ATM using PIM           April 1998


4. Router behavior

   This document requires that each router within a LIS knows IP and ATM
   addresses of all other routers within the LIS. The mapping between IP
   and ATM addresses may be provided by an ARP server [RFC 2225], or by
   any other means (e.g., static configuration).

   Each PIM router within a LIS is required to maintain a single
   (shared) point-to-multipoint distribution VC rooted at the router
   with all other PIM routers in the LIS as the leaf nodes. The VC is
   expected to be used for forwarding of multicast traffic (both data
   and control) among routers within the LIS. For example, this VC would
   be used for distributing PIM [PIM-SM] control messages (Join/Prune
   messages).

   In addition, if a PIM router receives a IGMP report from an non-PIM
   neighbor, then the router may add the reporter to the existing shared
   distribution VC or to the group specific distribution VC (if it
   exists). The PIM router may also create a specific VC for this IGMP
   proxy.

4.1. Establishing Dedicated, Per Group Point-to-Multipoint VCs

   Routers may also maintain group specific, dedicated point-to-
   multipoint VCs. In particular, an upstream router for a group may
   choose to become the root of a group specific point-to-multipoint VC
   whose leaves are the downstream routers that have directly connected
   or downstream receivers for the group. While the criteria for
   establishing a group specific point-to-multipoint VC are local to a
   router, issues such as the volume of traffic associated with the
   group and the fanout factor within the LIS should be considered.
   Finally, note that a router must minimally support a single shared
   point-to-multipoint VC for distribution of control messages and data
   (to all group addresses).

   A router can choose to establish a dedicated point-to-multipoint VC
   (or add another leaf to an already established dedicated point-to-
   multipoint VC) when it receives a PIM Join or IGMP report messages
   from another device in the same LIS. When a router that is the root
   of a point-to-multipoint VC receives PIM Prune message or IGMP leave,
   it removes the originator of the message from its dedicated point-
   to-multipoint VC.









Farinacci, et. al.            Experimental