Cisco Systems 78-11741-02 manual IGMPv3 Host Signalling, Igmp v3lite Host Signalling, IPC-461

Configuring Source Specific Multicast

IGMPv3 Host Signalling

If SSM is deployed in a network already configured for PIM-SM (Cisco IOS Release 12.0 or later releases is recommended), then only the last hop routers must be upgraded to a Cisco IOS software image that supports SSM. Routers that are not directly connected to receivers do not have to upgrade to a Cisco IOS software image that supports SSM. In general, these nonlast hop routers must only run PIM-SM in the SSM range, and may need additional access control configuration to suppress MSDP signalling, registering, or PIM-SM shared tree operations from occurring within the SSM range.

The SSM mode of operation is enabled by configuring the SSM range through the ip pim ssm global configuration command. This configuration has the following effects:

•For groups within the SSM range, (S, G) channel subscriptions are accepted through IGMPv3 INCLUDE mode membership reports, IGMP v3lite, or URD (each of these methods must be configured on a per-interface basis). IGMP v3lite and URD (S, G) channel subscriptions are ignored for groups outside the SSM range.

Both IGMP v3lite and URD are based on utilizing existing application IGMP group membership and extending it with their respective (S, G) channel subscription mechanism, which is ignored by Cisco IOS software outside the SSM range of addresses. Within the SSM range, IGMP Version 1 (IGMPv1) or Version 2 (IGMPv2) group membership reports or IGMPv3 EXCLUDE mode membership reports are acted upon only in conjunction with an (S, G) specific membership report from URD or IGMP v3lite.

•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 will be accepted, generated, or forwarded.

IGMPv3 Host Signalling

IGMPv3 is the third version of the IETF standards track protocol in which hosts signal membership to last hop routers of multicast groups. IGMPv3 introduces the ability for hosts to 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.

For more information on IGMPv3, see the “Configuring IP Multicast Routing” chapter in this document.

IGMP v3lite Host Signalling

IGMP v3lite is a Cisco-developed transitional solution for application developers to immediately start programming SSM applications. It allows you to write and run SSM applications on hosts that do not yet support IGMPv3 in their operating system kernel.

Cisco IOS IP Configuration Guide

IPC-461