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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 48 Configuring IP Multicast Routing Configuring IP Multicast Routing
the IP addresses of sources from which they receive their traffic. The proposed standard approach for
channel subscription signalling use IGMP include mode membership reports, which are supported only
in IGMP version 3.
SSM IP Address Range
SSM can coexist with the ISM service by applying the SSM delivery model to a configured subset of the
IP multicast group address range. Cisco IOS software allows SSM configuration for the IP multicast
address range of 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 an address in the SSM
range (unless the application is modified to use an explicit (S, G) channel subscription).
SSM Operations
An established network, in which IP multicast service is based on PIM-SM, can support SSM services.
SSM can also be deployed alone in a network without the full range of protocols required for interdomain
PIM-SM (for example, MSDP, Auto-RP, or bootstrap router [BSR]) if only SSM service is needed.
If SSM is deployed in a network already configured for PIM-SM, only the last-hop routers support SSM.
Routers that are not directly connected to receivers do not require support for SSM. In general, these
not-last-hop routers must only run PIM-SM in the SSM range and might need additional access control
configuration to suppress MSDP signalling, registering, or PIM-SM shared tree operations from
occurring within the SSM range.
Use the ip pim ssm global configuration command to configure the SSM range and to enable SSM. This
configuration has the following effects:
• For groups within the SSM range, (S, G) channel subscriptions are accepted through IGMPv3
include-mode membership reports.
• PIM operations within the SSM range of addresses change to PIM-SSM, a mode derived from
PIM-SM. In this mode, only PIM (S, G) join and prune messages are generated by the router, and
no (S, G) rendezvous point tree (RPT) or (*, G) RPT messages are generated. Incoming messages
related to RPT operations are ignored or rejected, and incoming PIM register messages are
immediately answered with register-stop messages. PIM-SSM is backward-compatible with
PIM-SM unless a router is a last-hop router. Therefore, routers that are not last-hop routers can run
PIM-SM for SSM groups (for example, if they do not yet support SSM).
• No MSDP source-active (SA) messages within the SSM range are accepted, generated, or
forwarded.
IGMPv3 Host Signalling
In IGMPv3, hosts signal membership to last hop routers of multicast groups. Hosts can signal group
membership with filtering capabilities with respect to sources. A host can either signal that it wants to
receive traffic from all sources sending to a group except for some specific sources (called exclude
mode), or that it wants to receive traffic only from some specific sources sending to the group (called
include mode).
IGMPv3 can operate with both ISM and SSM. In ISM, both exclude and include mode reports are
applicable. In SSM, only include mode reports are accepted by the last-hop router. Exclude mode reports
are ignored.