Time to Live (TTL)

Time to Live (TTL)
You can also control the delivery of IP multicast packets through the TTL counter and TTL
thresholds. The TTL counter is decremented by one every time the packet hops a router. After
the TTL counter is set to zero, the packet is discarded.
Thresholds are used to achieve higher granularity and greater control within one’s own
network. Thresholds are applied to specified interfaces of multicast-enabled routers. The
router compares the threshold value of the multicast packet to the value specified in the interface
configuration. If the TTL value of the packet is greater than or equal to the TTL threshold
configured for the interface, the packet is forwarded through that interface.
TTL thresholds enable network administrators to bound their network and limit the distribution
of multicast packets beyond the boundaries. This is accomplished by setting high
values for outbound external interfaces. The maximum value for the TTL threshold is 255.
Refer to Figure 19.15 to see how network boundaries can be set to limit distribution of
multicast traffic.