HP ProCurve 5300xl Series Management Manual page 145

Syntax:
ip pim
[ ttl-threshold < 0 - 255 > ]
vlan < vid > ip pim
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.
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. On a Switch Series 5300XL device,
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.)
Example of Configuring PIM-DM Operation at the VLAN Level. The
network in figure 5-4 uses VLAN 25 for multicast traffic. However, this VLAN
is multinetted and there is only one subnet (25.38.10.x) in VLAN 25 that is
common to all three routing switches. Thus, when configuring VLAN 25 on
these routing switches to perform multicast routing, it is necessary to use ip
pim < source-ip-address > to designate the common subnet as the source
address for outbound multicast traffic on VLAN 25. (If only identical subnets
were present in the multinetted VLAN 25 configuration on all three devices,
then the ip pim all command would be used instead.) Note that the other VLANs
in the network are not multinetted and therefore do not require the ip pim <
all | source-ip-address > option.
For this example, assume that the VLANs and IP addressing are already
configured on the routing switch.
PIM-DM (Dense Mode) on the 5300xl Switches
Configuring PIM-DM on the Series 5300xl Switches
5-19