350-601 · Question #359
A content delivery network sends video traffic to a multicast distribution device where the receiver requests the traffic from the multicast distribution device through an IGMP join message. When…
The correct answer is C. Reverse Path Forwarding. Reverse Path Forwarding (RPF) is the core mechanism used by multicast routers to prevent loops and ensure that multicast traffic received from a source (S) is forwarded correctly to interested receivers in a group (G).
Question
A content delivery network sends video traffic to a multicast distribution device where the receiver requests the traffic from the multicast distribution device through an IGMP join message. When the traffic reaches the multicast routing device from a CDN the switching network populates the multicast routing table in the group (S G) and the multicast distribution device sends the required traffic back to the receiver. Which feature is used to send back the trafic from the streamer to the receiver in the group (S G)?
Options
- ARP
- BIGMP
- CReverse Path Forwarding
- DSource Specific Multicast
How the community answered
(22 responses)- C95% (21)
- D5% (1)
Why each option
Reverse Path Forwarding (RPF) is the core mechanism used by multicast routers to prevent loops and ensure that multicast traffic received from a source (S) is forwarded correctly to interested receivers in a group (G).
Rendezvous Point (RP) is used in PIM-SM to build shared trees for initial group joins, but RPF is the forwarding mechanism that ensures traffic validity and prevents loops once a path from the source is established.
IGMP (Internet Group Management Protocol) is used by hosts to signal their membership in a multicast group to the local router, not for the router to forward traffic from the streamer to the receiver.
When a multicast packet arrives on a router interface for a specific (S,G) entry, the router performs an RPF check. This check verifies if the incoming interface is the shortest path back to the source (S); if it is, the packet is considered valid and forwarded out to interfaces with interested receivers, otherwise it is dropped to prevent forwarding loops.
Source Specific Multicast (SSM) defines the (S,G) multicast model where receivers explicitly specify the source, but RPF is the underlying forwarding mechanism that handles traffic delivery within that model.
Concept tested: Multicast Reverse Path Forwarding (RPF)
Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipmulti/command/imc-cr-book/imc-cr-p2.html
Topics
Community Discussion
No community discussion yet for this question.