Multicast Routing
IP multicasting is a mechanism that conserves network bandwidth by delivering a stream of
information simultaneously to multiple recipients. Some common applications that take
advantage of IP multicasting include the following:
■ Video conferencing
■ Distance learning
■ News feeds
IP multicasting actually involves sending an IP packet to a single multicast IP address.
Routers send Internet Group Management Protocol (IGMP) query messages to locate hosts
that belong to any multicast groups (wishing to receive specific multicast traffic). Any host
that wishes to receive multicast traffic must join the multicast group by using an IGMP report
message that indicates all the multicast groups to which it belongs. When a host no longer
wishes to receive a multicast data stream, it sends an IGMP Leave message to the multicast
router.
With the introduction of software version 7.0, the Security Appliances can now support PIM
sparse-mode. Sparse-mode PIM defines a rendezvous point (RP) for the Security Appliance
that keeps track of multicast groups. Instead of flooding the network to determine the status
of the multicast member, a receiver that wants to send data can register with the RP. Sparsemode
PIM assumes that hosts do not want to participate in multicast traffic unless they
specifically request it.
If several Security Appliances are participating in multicast traffic on a network segment,
PIM requires that a designated router (DR) be assigned. A DR is responsible for sending PIM
register, join, and prune messages to the RP. This reduces the amount of noise that can be
created if each multicast Security Appliance sends duplicate requests to the RP.
You can configure your Security Appliance to act as a Stub Multicast Router (SMR) because
it forwards requests only between end hosts and multicast routers. Instead of supporting the
functionality of a fully operational multicast router, the Security Appliance functions only as
an IGMP proxy agent. To illustrate the configuration tasks associated with configuring your
Security Appliance as an SMR, you need to understand the following topics:
■ Multicast commands
■ Inbound multicast traffic
■ Outbound multicast traffic
■ Debugging multicast