Cisco Systems 78-11741-02 Configuring the TTL Threshold, Disabling Fast Switching of IP Multicast

Configuring IP Multicast Routing

Configuring the TTL Threshold

Configuring the TTL Threshold

The TTL value controls whether packets are forwarded out of an interface. You specify the TTL value in hops. Only multicast packets with a TTL greater than the interface TTL threshold are forwarded on the interface. The default value is 0, which means that all multicast packets are forwarded on the interface. To change the default TTL threshold value, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)#ip multicast ttl-threshold	Configures the TTL threshold of packets being forwarded out an
ttl-value	interface.

Disabling Fast Switching of IP Multicast

Fast switching of IP multicast packets is enabled by default on all interfaces (including generic routing encapsulation [GRE] and DVMRP tunnels), with one exception: It is disabled and not supported over

X.25 encapsulated interfaces. Note the following properties of fast switching:

•If fast switching is disabled on an incoming interface for a multicast routing table entry, the packet is sent at process level for all interfaces in the outgoing interface list.

•If fast switching is disabled on an outgoing interface for a multicast routing table entry, the packet is process-level switched for that interface, but may be fast switched for other interfaces in the outgoing interface list.

Disable fast switching if you want to log debug messages, because when fast switching is enabled, debug messages are not logged.

To disable fast switching of IP multicast, use the following command in interface configuration mode:

Command	Purpose
Router(config-if)# no ip mroute-cache	Disables fast switching of IP multicast.

SAP Listener Support Configuration Task List

To configure Session Announcement Protocol (SAP) listener support, perform the tasks described in the following sections. The task in the first section is required; the task in the remaining section is optional.

•Enabling SAP Listener Support (Required)

•Limiting How Long a SAP Cache Entry Exists (Optional)

Enabling SAP Listener Support

Use session description and announcement protocols and applications to assist the advertisement of multicast multimedia conferences and other multicast sessions and to communicate the relevant session setup information to prospective participants. Sessions are described by the Session Description Protocol (SDP), which is defined in RFC 2327. SDP provides a formatted, textual description of session

Cisco IOS IP Configuration Guide

IPC-415