Cisco Cisco IOS Software Release 12.0(15)S
Source Specific Multicast with IGMPv3, IGMP v3lite, and URD
Feature Overview
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Cisco IOS Release 12.0(15)S
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Internet Group Management Protocol Version 3 lite (IGMP v3lite)
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URL Rendezvous Directory (URD)
PIM-SSM is the routing protocol that supports the implementation of SSM and is derived from PIM
sparse mode (PIM-SM). IGMP is the Internet Engineering Task Force (IETF) standards track protocol
used for hosts to signal multicast group membership to routers. Version 3 of this protocol supports
source filtering, which is required for SSM. To run SSM with IGMPv3, SSM must be supported in the
Cisco IOS router, the host where the application is running, and the application itself. IGMP v3lite and
URD are two Cisco-developed transition solutions that enable the immediate development and
deployment of SSM services, without the need to wait for the availability of full IGMPv3 support in
host operating systems and SSM receiver applications. IGMP v3lite is a solution for application
developers that allows immediate development of SSM receiver applications switching to IGMPv3 as
soon as it becomes available. URD is a solution for content providers and content aggregators that
enables them to deploy receiver applications that are not yet SSM enabled (through support for
IGMPv3). IGMPv3, IGMP v3lite, and URD interoperate with each other, so that both IGMP v3lite and
URD can easily be used as transitional solutions toward full IGMPv3 support in hosts.
sparse mode (PIM-SM). IGMP is the Internet Engineering Task Force (IETF) standards track protocol
used for hosts to signal multicast group membership to routers. Version 3 of this protocol supports
source filtering, which is required for SSM. To run SSM with IGMPv3, SSM must be supported in the
Cisco IOS router, the host where the application is running, and the application itself. IGMP v3lite and
URD are two Cisco-developed transition solutions that enable the immediate development and
deployment of SSM services, without the need to wait for the availability of full IGMPv3 support in
host operating systems and SSM receiver applications. IGMP v3lite is a solution for application
developers that allows immediate development of SSM receiver applications switching to IGMPv3 as
soon as it becomes available. URD is a solution for content providers and content aggregators that
enables them to deploy receiver applications that are not yet SSM enabled (through support for
IGMPv3). IGMPv3, IGMP v3lite, and URD interoperate with each other, so that both IGMP v3lite and
URD can easily be used as transitional solutions toward full IGMPv3 support in hosts.
How SSM Differs from Internet Standard Multicast
The current IP multicast infrastructure in the Internet and many enterprise intranets is based on the
PIM-SM protocol and Multicast Source Discovery Protocol (MSDP). These protocols have proven to
be reliable, extensive, and efficient. However, they are bound to the complexity and functionality
limitations of the Internet Standard Multicast (ISM) service model. For example, with ISM, the network
must maintain knowledge about which hosts in the network are actively sending multicast traffic. With
SSM, this information is provided by receivers through the source address(es) relayed to the last hop
routers by IGMPv3, IGMP v3lite, or URD. SSM is an incremental response to the issues associated with
ISM and is intended to coexist in the network with the protocols developed for ISM. In general, SSM
provides a more advantageous IP multicast service for applications that utilize SSM.
PIM-SM protocol and Multicast Source Discovery Protocol (MSDP). These protocols have proven to
be reliable, extensive, and efficient. However, they are bound to the complexity and functionality
limitations of the Internet Standard Multicast (ISM) service model. For example, with ISM, the network
must maintain knowledge about which hosts in the network are actively sending multicast traffic. With
SSM, this information is provided by receivers through the source address(es) relayed to the last hop
routers by IGMPv3, IGMP v3lite, or URD. SSM is an incremental response to the issues associated with
ISM and is intended to coexist in the network with the protocols developed for ISM. In general, SSM
provides a more advantageous IP multicast service for applications that utilize SSM.
ISM service is described in RFC 1112. This service consists of the delivery of IP datagrams from any
source to a group of receivers called the multicast host group. The datagram traffic for the multicast
host group consists of datagrams with an arbitrary IP unicast source address S and the multicast group
address G as the IP destination address. Systems will receive this traffic by becoming members of the
host group. Membership to a host group simply requires signalling the host group through IGMP
Version 1, 2, or 3.
source to a group of receivers called the multicast host group. The datagram traffic for the multicast
host group consists of datagrams with an arbitrary IP unicast source address S and the multicast group
address G as the IP destination address. Systems will receive this traffic by becoming members of the
host group. Membership to a host group simply requires signalling the host group through IGMP
Version 1, 2, or 3.
In SSM, delivery of datagrams is based on (S, G) channels. Traffic for one (S, G) channel consists of
datagrams with an IP unicast source address S and the multicast group address G as the IP destination
address. Systems will receive this traffic by becoming members of the (S, G) channel. In both SSM and
ISM, no signalling is required to become a source. However, in SSM, receivers must subscribe or
unsubscribe to (S, G) channels to receive or not receive traffic from specific sources. In other words,
receivers can receive traffic only from (S, G) channels to which they are subscribed, whereas in ISM,
receivers need not know the IP addresses of sources from which they receive their traffic. The proposed
standard approach for channel subscription signalling utilizes IGMP INCLUDE mode membership
reports, which are supported only in Version 3 of IGMP.
datagrams with an IP unicast source address S and the multicast group address G as the IP destination
address. Systems will receive this traffic by becoming members of the (S, G) channel. In both SSM and
ISM, no signalling is required to become a source. However, in SSM, receivers must subscribe or
unsubscribe to (S, G) channels to receive or not receive traffic from specific sources. In other words,
receivers can receive traffic only from (S, G) channels to which they are subscribed, whereas in ISM,
receivers need not know the IP addresses of sources from which they receive their traffic. The proposed
standard approach for channel subscription signalling utilizes IGMP INCLUDE mode membership
reports, which are supported only in Version 3 of IGMP.
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. The Internet Assigned Numbers Authority (IANA) has reserved
the address range 232.0.0.0 through 232.255.255.255 for SSM applications and protocols. Cisco IOS
software allows SSM configuration for an arbitrary subset of the IP multicast address range 224.0.0.0
the IP multicast group address range. The Internet Assigned Numbers Authority (IANA) has reserved
the address range 232.0.0.0 through 232.255.255.255 for SSM applications and protocols. Cisco IOS
software allows SSM configuration for an arbitrary subset of the IP multicast address range 224.0.0.0