Restrictions For Auto-Rp Enhancement; Information About Pim; Protocol Independent Multicast Overview; Pim Dense Mode - Cisco Catalyst 3850 series Configuration Manual

Configuring PIM

Restrictions for Auto-RP Enhancement

The simultaneous deployment of Auto-RP and bootstrap router (BSR) is not supported.
Related Topics
Setting Up Auto-RP in a New Internetwork (CLI), on page 146
Auto-RP, on page 130

Information About PIM

Protocol Independent Multicast Overview

The Protocol Independent Multicast (PIM) protocol maintains the current IP multicast service mode of
receiver-initiated membership. PIM is not dependent on a specific unicast routing protocol; it is IP routing
protocol independent and can leverage whichever unicast routing protocols are used to populate the unicast
routing table, including Enhanced Interior Gateway Routing Protocol (EIGRP), Open Shortest Path First
(OSPF), Border Gateway Protocol (BGP), and static routes. PIM uses unicast routing information to perform
the multicast forwarding function.
Although PIM is called a multicast routing protocol, it actually uses the unicast routing table to perform the
reverse path forwarding (RPF) check function instead of building up a completely independent multicast
routing table. Unlike other routing protocols, PIM does not send and receive routing updates between routers.
PIM is defined in RFC 4601, Protocol Independent Multicast - Sparse Mode (PIM-SM)
PIM can operate in dense mode or sparse mode. The router can also handle both sparse groups and dense
groups at the same time (sparse-dense mode). The mode determines how the router populates its multicast
routing table and how the router forwards multicast packets it receives from its directly connected LANs.
For information about PIM forwarding (interface) modes, see the following sections:

PIM Dense Mode

PIM dense mode (PIM-DM) uses a push model to flood multicast traffic to every corner of the network. This
push model is a method for delivering data to the receivers without the receivers requesting the data. This
method is efficient in certain deployments in which there are active receivers on every subnet in the network.
In dense mode, a router assumes that all other routers want to forward multicast packets for a group. If a router
receives a multicast packet and has no directly connected members or PIM neighbors present, a prune message
is sent back to the source. Subsequent multicast packets are not flooded to this router on this pruned branch.
PIM builds source-based multicast distribution trees.
PIM-DM initially floods multicast traffic throughout the network. Routers that have no downstream neighbors
prune back the unwanted traffic. This process repeats every 3 minutes.
Routers accumulate state information by receiving data streams through the flood and prune mechanism.
These data streams contain the source and group information so that downstream routers can build up their
multicast forwarding table. PIM-DM supports only source trees--that is, (S,G) entries--and cannot be used to
build a shared distribution tree.
OL-32598-01
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3.6E (Catalyst 3850 Switches)
Restrictions for Auto-RP Enhancement
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