Multicast routing is essentially routing backwards . To forward multicast traffic, a router checks if the incoming interface is the same interface it would use to send traffic back to the source. If RPF fails, the multicast packet is dropped. This is the #1 troubleshooting point in multicast labs.
Do not read this book linearly if you are studying for the CCIE Lab. Instead, group the topics by weight and dependency. Routing TCP IP- Volume II -CCIE Professional Development
: Detailed coverage of Protocol Independent Multicast (PIM) in Dense, Sparse, and Bidirectional modes, including scaling and troubleshooting. Network Address Translation (NAT) Multicast routing is essentially routing backwards
Explaining the why before the how . Doyle unpacks the historical context and engineering problems a protocol was designed to solve. and Bidirectional modes
