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Configuring IP Multicast Routing
Configuring the TTL Threshold
IPC-415
Cisco IOS IP Configuration Guide
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:
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:
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
Command Purpose
Router(config-if)# ip multicast ttl-threshold
ttl-value
Configures the TTL threshold of packets being forwarded out an
interface.
Command Purpose
Router(config-if)# no ip mroute-cache
Disables fast switching of IP multicast.