Protocol Independent Multicast - Source Specific Multicast (Pim-Ssm); Internet Group Management Protocol (Igmp) - Alcatel Router User Manual

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Chapter : Multicasting

Protocol Independent Multicast - Source Specific Multicast (PIM-SSM)

PIM-SSM Command

Internet Group Management Protocol (IGMP)

Router User Guide
By running PIM-SSM and IGMPv3, you can implement a Source Specific Multicast (SSM) service
model in your network. PIM-SSM functionality is the subset of PIM-SM functionality dealing only
with source-specific distribution trees. IGMPv3 provides a way to detect channel subscriptions; for
example, host-initiated (S,G) joins where G falls within the defined range of SSM multicast group
addresses.
PIM-SSM can be run in the absence of IGMPv3. Even when they are both running, they do not need
to run on the same interfaces. For example, you might not want to run PIM-SSM (or PIM-SM, for
that matter) over an interface that leads to a stub network. Similarly, if a network cannot contain
local IGMPv3 receivers (for example, on a DMZ network), then there is no need to run IGMPv3.
ip pim ssm-range
Internet Group Management Protocol (IGMP) is enabled on hosts and routers that want to receive
multicast traffic. IGMP informs locally-attached routers of their multicast group memberships. Hosts
inform routers of the groups of which they are members by multicasting IGMP Group Membership
Reports. When multicast routers listen for these reports, they can exchange group membership
information with other multicast routers. This reporting system allows distribution trees to be formed
to deliver multicast datagrams. The original version of IGMP was defined in RFC 1112, Host
Extensions for IP Multicasting. Extensions to IGMP, known as IGMP version 2.
IGMPv2 improves performance and supports the following message types:
IGMP Query: IGMP Query is sent by the router to know which groups have members on the
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attached network.
IGMP Reports: IGMP reports are sent as a response to the query by hosts to announce their
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group membership. Reports can be sent "unsolicited" when the hosts come up.
IGMP Leaves: IGMP Leaves are sent by the host when it relinquishes membership of a
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group.
The latest extension to the IGMP standard is Version 3, which includes interoperability with version
2 and version 1 hosts, also provides support for source filtering. Source filtering enables a multicast
receiver host to signal to a router which groups it wants to receive multicast traffic from, and from
which source(s) this traffic is expected. This membership information enables the router to forward
traffic only from those sources from which receivers requested the traffic.
IGMPv3 supports applications that explicitly signal sources from which they want to receive traffic.
With IGMPv3, receivers signal membership to a multicast host group in the following two modes:
INCLUDE mode: In this mode, the receiver announces membership to a host group and
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provides a list of IP addresses (the INCLUDE list) from which it wants to receive traffic.
EXCLUDE mode: In this mode, the receiver announces membership to a host group and
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provides a list of IP addresses (the EXCLUDE list) from which it does not want to receive
traffic. This indicates that the host wants to receive traffic only from other sources whose IP
addresses are not listed in the EXCLUDE list. To receive traffic from all sources, like in the
case of the Internet Standard Multicast (ISM) service model, a host expresses EXCLUDE
mode membership with an empty EXCLUDE list.
IGMPv3 is used by the hosts to express their desire to be a part of the source-specific multicast
(SSM) which is an emerging standard used by routers to direct multicast traffic to the host only if its
is from a specific source.