Explanation: #show ip mroute
#show ip pim interface
#show ip igmp group
#show ip pim neighbor

Explanation:
Reverse Path Forwarding (RPF)
RPF is a fundamental concept in multicast routing that enables routers to correctly forward
multicast traffic down the distribution tree. RPF makes use of the existing unicast routing
table to determine the upstream and downstream neighbors. A router will only forward a
multicast packet if it is received on the upstream interface.
This RPF check helps to guarantee that the distribution tree will be loop free.
RPF Check
When a multicast packet arrives at a router, the router will perform an RPF check on the
packet. If the RPF check is successful, the packet will be forwarded. Otherwise it will be
dropped.
For traffic flowing down a source tree, the RPF check procedure works as follows:
Step 1. Router looks up the source address in the unicast routing table to determine if it
has arrived on the interface that is on the reverse path back to the source.
Step 2. If packet has arrived on the interface leading back to the source, the RPF check is
successful and the packet will be forwarded.
Step 3. If the RPF check in 2 fails, the packet is dropped.

Explanation:
Source-Based RTBH Filtering
With destination-based black holing, all traffic to a specific destination is dropped after the
black hole has been activated, regardless of where it is coming from. Obviously, this could
include legitimate traffic destined for the target. Source-based black holes provide the
ability to drop traffic at the network edge based on a specific source address or range of
source addresses.
If the source address (or range of addresses) of the attack can be identified (spoofed or
not), it would be better to drop all traffic at the edge based on the source address,
regardless of the destination address. This would permit legitimate traffic from other
sources to reach the target. Implementation of source-based black hole filtering depends
on Unicast Reverse Path Forwarding (uRPF), most often loose mode uRPF.
Loose mode uRPF checks the packet and forwards it if there is a route entry for the source
IP of the incoming packet in the router forwarding information base (FIB). If the router does
not have an FIB entry for the source IP address, or if the entry points to a null interface, the
Reverse Path Forwarding (RPF) check fails and the packet is dropped, as shown in Figure
2. Because uRPF validates a source IP address against its FIB entry, dropping traffic from
specific source addresses is accomplished by configuring loose mode uRPF on the
external interface and ensuring the RPF check fails by inserting a route to the source with a
next hop of Null0.
This can be done by using a trigger device to send IBGP updates. These updates set the
next hop for the source IP to an unused IP address that has a static entry at the edge,
setting it to null as shown in Figure 2.

Explanation:
PIM-SSM Operations
PIM in Source Specific Multicast operation uses information found on source addresses for
a multicast group provided by receivers and performs source filtering on traffic.
By default, PIM-SSM operates in the 232.0.0.0/8 multicast group range for IPv4 and
ff3x::/32 (where x is any valid scope) in IPv6. To configure these values, use the ssm range
command.
If SSM is deployed in a network already configured for PIM-SM, only the last-hop routers
must be upgraded with Cisco IOS XR software that supports the SSM feature.
No MSDP SA messages within the SSM range are accepted, generated, or forwarded