Setting the multicast datagram time-to-live (router hop-count) threshold for the VLAN
Syntax:
ip pim-dense [ttl-threshold[0-255]]
vlan[vid]ip pim-dense [ttl-threshold[0-255]]
Sets the multicast datagram time-to-live (router hop-count) threshold for the VLAN. Any IP multicast datagrams or state-refresh packets with a TTL less than this threshold will not be forwarded out the interface. The default value of 0 means all multicast packets are forwarded out the interface.
The VLAN connected to the multicast source does not receive state refresh packets and thus is not state-refresh capable. Downstream VLANs in the switches covered in this guide are state-refresh capable. This parameter provides a method for containing multicast traffic within a network, or even within specific areas of a network. Initially, the multicast traffic source sets a TTL value in the packets it transmits. Each time one of these packets passes through a multicast routing device, the TTL setting decrements by 1. If the packet arrives with a TTL lower than the
mroute ttl-threshold, the routing switch does not forward the packet.
Changing this parameter on a routing switch requires knowledge of the TTL setting of incoming multicast packets:
A value that is too high can allow multicast traffic to go beyond your internal network.
A value that is too low may prevent some intended hosts from receiving the desired multicast traffic.
Default: 0—forwards multicast traffic regardless of packet TTL setting