Cisco 3560G 48TS Software Configuration Guide - Page 699

IGMP Version 1, Understanding PIM

Page 699 highlights

Chapter 32 Configuring IP Multicast Routing Understanding Cisco's Implementation of 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: • 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. 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: • 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 78-16156-01 Catalyst 3560 Switch Software Configuration Guide 32-3

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32-3
Catalyst 3560 Switch Software Configuration Guide
78-16156-01
Chapter 32
Configuring IP Multicast Routing
Understanding Cisco’s Implementation of 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:
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.
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:
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