Protocol Independent Multicast - Sparse Mode (Pim-Sm) - Fujitsu Siemens Computers PRIMERGY BX Description

Features of the Switch
when a new host wants to join a group, and assert messages are used to shut off duplicate
flows.
PRIMERGY BX600 PIM-DM can be enabled but will only become operational when both
routing and IGMP are enabled and operational.
Protocol Independent Multicast – Sparse Mode (PIM-SM)
Protocol Independent Multicast sparse mode (PIM-SM), like PIM dense mode (PIM-DM),
uses the unicast routing table to perform the Reverse Path Forwarding (RPF) check function
instead of maintaining a separate multicast route table. Therefore, regardless of which unicast
routing protocol(s) is (are) used to populate the unicast routing table (including static routes),
PIM-SM uses this information to perform multicast forwarding; hence, it too is protocol
independent.
The unicast routing table is used to determine the path that PIM control messages such as
Join messages take to get to the source subnet, and data flows along the reverse path of the
Join messages. Based on received Join/Prune messages, routers maintain a set of mappings
between the incoming interfaces and outgoing interfaces for each known multicast group.
PIM-SM uses two scenarios in the network for building information trees, which are used
for inter-domain routing. They are
- Source sending data for a multicast group
- Receiver of a multicast group requesting data
In both the above scenarios PIM-SM makes use of the following concepts
Rendezvous Point (RP): RP is the root of a shared distribution tree down which all multicast
traffic flows.
Designated Router (DR): DR is responsible for sending 'Join' messages to the RP for
members on the network and for sending 'Register' messages to the RP for sources on the
network.
PIM-SM is used to efficiently route multicast traffic to multicast groups that may span wide
area networks and where bandwidth is a constraint. PIM-SM uses shared trees by default and
implements source-based trees for efficiency this data threshold rate is used to toggle between
trees. PIM-SM assumes that no hosts want the multicast traffic unless they specifically ask for
it. It creates a shared distribution tree centered on a defined "rendezvous point" (RP) from
which source traffic is relayed to the receivers. Senders first send the multicast data to the RP,
which in turn sends the data down the shared tree to the receivers. Shared trees centered on a
RP do not necessarily provide the shortest/optimal path. In such cases PIM-SM provides a
means to switch to more efficient source specific trees.
The PRIMERGY BX600 IP Multicast implementation of PIM-SM supports both automatic
RP router election and user specified RP designation.
Automatic RP determination
The RP for a given IP group address (G) may be determined by the protocols specified in
section 2.6 of RFC 2362. PRIMERGY BX600 supports these protocols.
Static RP designation
The user may specify which router shall be the RP for a given IP group address via the
user interface. This information will be used to designate the RP for the group if no
information for the group address has been obtained via the automatic RP determination
protocols. Note that if the router learns of an RP for a group via the automatic mechanism
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Introduction
Lan Switch and Router Blade