The figure shows an example of a successful RPF check.
Figure 9: RPF Check Succeeds
In this example, the multicast packet has arrived on interface S1. The router refers to the unicast routing table
and finds that S1 is the correct interface. The RPF check passes, and the packet is forwarded.
PIM uses both source trees and RP-rooted shared trees to forward datagrams. The RPF check is performed
differently for each:
•
If a PIM router or multilayer device has a source-tree state (that is, an (S, G) entry is present in the
multicast routing table), it performs the RPF check against the IP address of the source of the multicast
packet.
•
If a PIM router or multilayer device has a shared-tree state (and no explicit source-tree state), it performs
the RPF check on the RP address (which is known when members join the group).
DVMRP and dense-mode PIM use only source trees and use RPF.
DVMRP is not supported on the device.Note
Sparse-mode PIM uses the RPF lookup function to decide where it needs to send joins and prunes:
•
(S, G) joins (which are source-tree states) are sent toward the source.
•
(*,G) joins (which are shared-tree states) are sent toward the RP.
Default PIM Routing Configuration
This table displays the default PIM routing configuration for the device.
Table 14: Default Multicast Routing Configuration
Default SettingFeature
Disabled on all interfaces.Multicast routing
Version 2.PIM version
No mode is defined.PIM mode
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3.6E (Catalyst 3850 Switches)
140 OL-32598-01
Configuring PIM
Default PIM Routing Configuration
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