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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 40 Configuring IP Multicast Routing Understanding Cisco’s Implementation of IP Multicast Routing

IGMP Version 1

IGMP Version 1 (IGMPv1) primarily uses a query-response model that enables the multicast router and
multilayer switch to find which multicast groups are active (have one or more hosts interested in a
multicast group) on the local subnet. IGMPv1 has other processes that enable a host to join and leave a
multicast group. For more information, see RFC 1112.

IGMP Version 2

IGMPv2 extends IGMP functionality by providing such features as the IGMP leave process to reduce
leave latency, group-specific queries, and an explicit maximum query response time. IGMPv2 also adds
the capability for routers to elect the IGMP querier without depending on the multicast protocol to
perform this task. For more information, see RFC 2236.
Understanding PIM
PIM is called protocol-independent: regardless of the unicast routing protocols used to populate the
unicast routing table, PIM uses this information to perform multicast forwarding instead of maintaining
a separate multicast routing table.
PIM is defined in RFC 2362, Protocol-Independent Multicast-Sparse Mode (PIM-SM): Protocol
Specification. PIM is defined in these Internet Engineering Task Force (IETF) Internet drafts:
• Protocol Independent Multicast (PIM): Motivation and Architecture
• Protocol Independent Multicast (PIM), Dense Mode Protocol Specification
• Protocol Independent Multicast (PIM), Sparse Mode Protocol Specification
• draft-ietf-idmr-igmp-v2-06.txt, Internet Group Management Protocol, Version 2
• draft-ietf-pim-v2-dm-03.txt, PIM Version 2 Dense Mode
This section includes this information about PIM:
• PIM Versions, page 40-3
• PIM Modes, page 40-4
• PIM Stub Routing, page 40-4
• IGMP Helper, page 40-5
• Auto-RP, page 40-6
• Bootstrap Router, page 40-6
• Multicast Forwarding and Reverse Path Check, page 40-7

PIM Versions

PIMv2 includes these improvements over PIMv1:
• A single, active rendezvous point (RP) exists per multicast group, with multiple backup RPs. This
single RP compares to multiple active RPs for the same group in PIMv1.
• A bootstrap router (BSR) provides a fault-tolerant, automated RP discovery and distribution
mechanism that enables routers and multilayer switches to dynamically learn the group-to-RP
mappings.