User guide

Configuring a Multicast Border Router Configuring a Multicast Border Router
page 8-4 OmniSwitch AOS Release 7 Advanced Routing Configuration Guide March 2015
PIM Overview
This section provides a brief overview of the OmniSwitch PIM implementation. The use of PIM through-
out this chapter refers to PIM-DM and PIM-SM. For more detailed information about using PIM-SM and
PIM-DM, see Chapter 7, “Configuring PIM.”
Protocol-Independent Multicast (PIM) is an IP multicast routing protocol that uses routing information
provided by unicast routing protocols, such as RIP and OSPF. Note that PIM is not dependent on any
particular unicast routing protocol. Sparse mode PIM (PIM-SM) contrasts with flood-and-prune dense
mode multicast protocols, such as DVMRP and PIM Dense Mode (PIM-DM), in that multicast forward-
ing in PIM-SM is initiated only through specific requests.
Downstream routers must explicitly join PIM-SM distribution trees to receive multicast streams on behalf
of directly connected receivers or other downstream PIM-SM routers. This paradigm of receiver-initiated
forwarding makes PIM ideal for network environments where receiver groups are thinly populated and
bandwidth conservation is a concern, such as in wide area networks (WANs). PIM-DM uses RPF (Reverse
Path Forwarding) to prevent looping of multicast datagrams while flooding. If some areas of the network
do not have group members, PIM-DM will prune the forwarding branch by instantiating the prune state.
PIM-DM differs from PIM-SM in two essential ways:
• There are no periodic joins transmitted, only explicitly triggered prunes and grafts.
• There is no Rendezvous Point (RP). This is particularly important in networks that cannot tolerate a
single point of failure.
Configuring a Multicast Border Router
Before configuring this feature, PIM and DVMRP must first be loaded to memory via the ip load
command. In addition, an active PIM and DVMRP interface is required for these protocols to register with
the multicast border router (MBR) functionality. PIM and DVMRP have to register with the MBR so that
MBR can provide the functionality needed to support interoperability between the two protocols.
PIM and DVMRP are dynamically registered with MBR as soon as the first interface is enabled and opera-
tional for the particular protocol. In other words, as soon as the output of show ip mroute interface
command has the first interface enabled for the protocol, then the output of show ip mroute mbr will
show the protocol registered. For example:
-> show ip mroute interface
Interface Name IP Address TTL Multicast Protocol
---------------+---------------+------+--------------------
vlan-4 214.0.0.7 0 PIM
vlan-6 172.21.63.7 0 DVMRP
-> show ip mroute mbr
MBR Status = enabled,
Protocols Registered = DVMRP PIM
Note. It is possible for MBR to be enabled, but until both PIM and DVMRP have enabled at least one
interface and are active, then MBR functionality is still not operational.