Users Guide

00:01:59 15.1.1.10
LHR#
LHR# show ip pim tib
PIM Multicast Routing Table
Flags: S - Sparse, C - Connected, L - Local, P - Pruned,
R - RP-bit set, F - Register Flag, T - SPT-bit set, J - Join SPT,
K - Ack-Pending state
Timers: Uptime/Expires
Interface state: Interface, next-Hop, State/Mode
(*, 224.1.1.1), uptime 00:00:05, expires 00:00:54, RP 192.168.1.25, flags: SCJ
Incoming interface: ethernet1/1/29, RPF neighbor 1.1.1.2
Outgoing interface list:
vlan2001 Forward/Sparse 00:00:05/Never
(22.1.1.10, 224.1.1.1), uptime 00:00:05, expires 00:03:24, flags: T
Incoming interface: ethernet1/1/17, RPF neighbor 2.2.2.2
Outgoing interface list:
vlan2001 Forward/Sparse 00:00:05/Never
LHR# show ip pim mcache
PIM Multicast Routing Cache Table
(*, 224.1.1.1)
Incoming interface : ethernet1/1/29
Outgoing interface list :
vlan2001
(22.1.1.10,224.1.1.1)
Incoming interface : ethernet1/1/17
Outgoing interface list :
vlan2001
PIM-SSM
PIM-SSM uses source-based trees. A separate multicast distribution tree is built for each multicast source that sends data to
a multicast group. Each multicast distribution tree has as its root node a router near the source. Sources send data directly to
the root of the tree. PIM-SSM enables receivers to specify the source from which to receive data and the multicast group they
want to join. The receiver identifies a multicast data stream using the source and group address pair (S, G) instead of the group
address alone (*, G).
NOTE:
● PIM-SSM requires receivers to support IGMP version 3.
● The default PIM-SSM range is 232.0.0.0/8. The default range is always supported and the range can never be smaller
than the default.
● If the PIM-SSM group range overlaps with the multicast group range that the candidate RP advertises, the router
chooses the RP learned from the BSR and creates (*, G) entries instead of (S, G) entries.
Advantages of PIM-SSM
Advantages of PIM-SSM include the following:
● PIM-SSM forwards multicast traffic from a single source to a subnet. Other versions of PIM requires the receiver to
subscribe to a group. The receiver receives traffic not just from the source that it is interested in, but from all the sources
that send to that group. PIM-SSM requires the receiver to specify the sources in which they are interested in to avoid
receiving unnecessary traffic.
● PIM-SSM is more efficient than PIM-SM because it immediately creates shortest path trees (SPT) to the source rather than
using shared trees. PIM-SM requires a shared tree rooted at the RP because IGMPv2 receivers do not express the source
information in their membership reports. Multicast traffic passes from the source to the receiver through the RP, until the
last hop router (LHR) learns the source address, at which point it switches to the SPT.
Multicast
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