Cisco Systems 78-11741-02 Limiting How Long a SAP Cache Entry Exists, Announcements, IPC-416

Configuring IP Multicast Routing

Enabling the Functional Address for IP Multicast over Token Ring LANs

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:

Command	Purpose
Router(config-if)# ip sap listen	Enables the Cisco IOS software to listen to Session Directory
	announcements.

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:

Command	Purpose
Router(config)# ip sap cache-timeout	Limits how long a SAP cache entry stays active in the cache.

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.

Cisco IOS IP Configuration Guide

IPC-416