Igmp Version 1; Understanding Pim - Cisco Catalyst 3750 Software Configuration Manual

Chapter 31 Configuring IP Multicast Routing
what members it has can vary from group to group and from time to time. A multicast group can be active
for a long time, or it can be very short-lived. Membership in a group can constantly change. A group that
has members can have no activity.
IP multicast traffic uses group addresses, which are class D addresses. The high-order bits of a Class D
address are 1110. Therefore, host group addresses can be in the range 224.0.0.0 through
239.255.255.255. Multicast addresses in the range 224.0.0.0 to 24.0.0.255 are reserved for use by
routing protocols and other network control traffic. The address 224.0.0.0 is guaranteed not to be
assigned to any group.
IGMP packets are sent using these IP multicast group addresses:
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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, refer to 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, refer to 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:
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78-15870-01
IGMP general queries are destined to the address 224.0.0.1 (all systems on a subnet).
IGMP group-specific queries are destined to the group IP address for which the switch is querying.
IGMP group membership reports are destined to the group IP address for which the switch is
reporting.
IGMP Version 2 (IGMPv2) leave messages are destined to the address 224.0.0.2
(all-multicast-routers on a subnet). In some old host IP stacks, leave messages might be destined to
the group IP address rather than to the all-routers address.
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
Understanding Cisco's Implementation of IP Multicast Routing
Catalyst 3750 Metro Switch Software Configuration Guide
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