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Configuring IP Multicast Routing
Enabling the Functional Address for IP Multicast over Token Ring LANs
IPC-416
Cisco IOS IP Configuration Guide
properties (for example, contact information, session lifetime, and the media) being used in the session
(for example, audio, video, and whiteboard) with their specific attributes like TTL scope, group address,
and User Datagram Protocol (UDP) port number.
Many multimedia applications rely on SDP for session descriptions. However, they may use different
methods to disseminate these session descriptions. For example, IP/TV relies on the Web to disseminate
session descriptions to participants. In this example, participants must know of a Web server that
provides the session information.
MBONE applications (for example, vic, vat, and wb) and other applications rely on multicast session
information sent throughout the network. In these cases, a protocol called Session Announcement
Protocol (SAP) is used to transport the SDP session announcements. SAP Version 2 uses the well-known
session directory multicast group 224.2.127.254 to disseminate SDP session descriptions for global
scope sessions and group 239.255.255.255 for administrative scope sessions.
Note The Session Directory (SDR) application is commonly used to send and receive SDP/SAP session
announcements.
To enable the Cisco IOS software to listen to Session Directory announcements, use the following
command on a multicast-enabled interface in interface configuration mode:
Limiting How Long a SAP Cache Entry Exists
By default, entries are deleted 24 hours after they were last received from the network. To limit how long
a SAP cache entry stays active in the cache, use the following command in global configuration mode:
Enabling the Functional Address for IP Multicast over
Token Ring LANs
By default, IP multicast datagrams on Token Ring LAN segments use the MAC-level broadcast address
0xFFFF.FFFF.FFFF. That default places an unnecessary burden on all devices that do not participate in
IP multicast. The IP Multicast over Token Ring LANs feature defines a way to map IP multicast
addresses to a single Token Ring MAC address.
This feature defines the Token Ring functional address (0xc000.0004.0000) that should be used over
Token Ring. A functional address is a severely restricted form of multicast addressing implemented on
Token Ring interfaces. Only 31 functional addresses are available. A bit in the destination MAC address
designates it as a functional address.
The implementation used by Cisco complies with RFC 1469, IP Multicast over Token-Ring Local Area
Networks.
Command Purpose
Router(config-if)# ip sap listen
Enables the Cisco IOS software to listen to Session Directory
announcements.
Command Purpose
Router(config)# ip sap cache-timeout
Limits how long a SAP cache entry stays active in the cache.