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41-4
Cisco ASR 901 Series Aggregation Services Router Software Configuration Guide
OL-23826-09
Chapter 41 IPv4 Multicast
Feature Overview
PIM SSM Address Range
SSM can coexist with the Internet Standard Multicast (ISM) service by applying the SSM delivery model
to a configured subset of the IP multicast group address range. The Cisco IOS software allows SSM
configuration for an arbitrary subset of the IP multicast address range 224.0.0.0 through
239.255.255.255. When an SSM range is defined, existing IP multicast receiver applications do not
receive any traffic when they try to use addresses in the SSM range (unless the application is modified
to use explicit (S, G) channel subscription).
For groups within the SSM range, (S, G) channel subscriptions are accepted through IGMPv3 INCLUDE
mode membership reports.
IGMP
IGMP is used to dynamically register individual hosts in a multicast group on a particular LAN. Enabling
PIM on an interface also enables IGMP. IGMP provides a means to automatically control and limit the
flow of multicast traffic throughout the network with the use of special multicast queriers and hosts.
For more information on IGMP, see the IP Multicast: IGMP Configuration Guide at:
http://www.cisco.com/en/US/docs/ios-xml/ios/ipmulti_igmp/configuration/xe-3s/imc_customizing_ig
mp.html
IGMPv1
IGMP version 1 is a simple protocol consisting of two messages. It provides the basic query-response
mechanism that allows the multicast device to determine which multicast groups are active and other
processes that enable hosts to join a multicast group. RFC 1112 defines the IGMPv1 host extensions for
IP multicasting.
IGMPv2
IGMP version 2 extends the functionality of IGMP, allowing such capabilities as the IGMP leave
process, group-specific queries, and an explicit maximum response time field. IGMPv2 also adds the
capability for devices to elect the IGMP querier without dependence on the multicast protocol to perform
this task. RFC 2236 defines IGMPv2.
IGMPv3
IGMP version 3 provides for source filtering, which enables a multicast receiver host to signal to a device
which groups it wants to receive multicast traffic from, and from which sources this traffic is expected.
In addition, IGMPv3 supports the link local address 224.0.0.22, which is the destination IP address for
IGMPv3 membership reports; all IGMPv3-capable multicast devices must listen to this address.
RFC 3376 defines IGMPv3.