Implementing Multicast Routing on Cisco IOS XR Software Cisco ASR 9000 Series Routers
Information About Implementing Multicast Routing
MCC-11
Multicast Configuration Guide
OL-
Figure 4 Designated Router Election on a Multiaccess Segment
Note DR election process is required only on multiaccess LANs. The last-hop router directly connected to the
host is the DR.
Rendezvous Points
When PIM is configured in sparse mode, you must choose one or more routers to operate as a rendezvous
point (RP). A rendezvous point is a single common root placed at a chosen point of a shared distribution
tree, as illustrated in
Figure 3. A rendezvous point can be either configured statically in each box or
learned through a dynamic mechanism.
PIM DRs forward data from directly connected multicast sources to the rendezvous point for distribution
down the shared tree. Data is forwarded to the rendezvous point in one of two ways:
• Encapsulated in register packets and unicast directly to the rendezvous point by the first-hop router
operating as the DR.
• Multicast forwarded by the RPF forwarding algorithm, described in the “Reverse-Path Forwarding”
section on page MCC-13, if the rendezvous point has itself joined the source tree.
The rendezvous point address is used by first-hop routers to send PIM register messages on behalf of a
host sending a packet to the group. The rendezvous point address is also used by last-hop routers to send
PIM join and prune messages to the rendezvous point to inform it about group membership. You must
configure the rendezvous point address on all routers (including the rendezvous point router).
A PIM router can be a rendezvous point for more than one group. Only one rendezvous point address
can be used at a time within a PIM domain. The conditions specified by the access list determine for
which groups the router is a rendezvous point.
Host receiver
Member of
239.1.1.1
Router C
Router A Router B
Source = 10.0.0.1
Group = 239.1.1.1
Source = 10.0.1.1
Group = 239.1.1.1
IGMPv3 message:
Join 10.0.0.1, 239.1.1.1
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