34-3
Cisco ME 3400 EthernetAccess Switch SoftwareConfiguration Guide
78-17058-01
Chapter34 Configuring IP Multicast Routi ng Understanding Cisco’s Implementation of IP Multicast Routing

IGMP Version 1

IGMP Version 1 (IGMPv1) primarily uses a query-response model that enables th e mu ltica st r oute r a nd
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 maintainin g
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

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.
•Sparse mode and dense mode are properties of a group, as opp ose d to a n in terfa ce . We strongly
recommend sparse-dense mode, as opposed to either sparse mode or dense mode only.
•PIM join and prune messages have more flexible encoding for multiple address families.
•A more flexible hello packet format replaces the query packet to encode current and future
capability options.
•Register messages to an RP specify whether they are s ent by a b ord er ro ut er or a d es ig na ted r oute r.
•PIM packets are no longer inside IGMP packets; they are standalone packets.