300-510 · Question #200
A network engineer recently deployed a wireless network for users at a new office to join video conferences wirelessly. The existing network consists of routers that are configured for EIGRP and BGP.
The correct answer is C. Configure the devices to send join messages toward a multicast SPT. PIM-SSM (Source-Specific Multicast) uses only the Shortest Path Tree (SPT) - there is no shared tree (RPT) and no Rendezvous Point (RP). For SSM to function, receivers must use IGMPv3 to express interest in a specific (Source, Group) pair, and PIM routers must send (S,G) Join mes
Question
A network engineer recently deployed a wireless network for users at a new office to join video conferences wirelessly. The existing network consists of routers that are configured for EIGRP and BGP. Which are located at several data centers in different physical locations. The engineer configured PIM-SSM within a single domain from a single source. However, during the testing phase, the video conference failed to work for any of the users. The IPs are reachable and firewalls in the network are configured correctly to allow the traffic. Which action resolves the issue?
Options
- AConfigure PIM dense mode to replace P1M-SSM.
- BConfigure PIM dense mode with multidomain multicast
- CConfigure the devices to send join messages toward a multicast SPT
- DConfigure PIM sparse mode to replace PIM-SSM.
How the community answered
(39 responses)- A3% (1)
- B8% (3)
- C79% (31)
- D10% (4)
Explanation
PIM-SSM (Source-Specific Multicast) uses only the Shortest Path Tree (SPT) - there is no shared tree (RPT) and no Rendezvous Point (RP). For SSM to function, receivers must use IGMPv3 to express interest in a specific (Source, Group) pair, and PIM routers must send (S,G) Join messages directly toward the multicast source along the SPT. If the devices are not generating (S,G) joins toward the SPT - for example, if they are configured for ASM behavior or if IGMPv3 is not enabled on the last-hop routers - the multicast stream will never be established. Replacing SSM with PIM Dense Mode (options A or B) would be architecturally incorrect for this deployment. PIM Sparse Mode (option D) would require an RP and shared-tree infrastructure that SSM intentionally avoids. The fix is ensuring (S,G) join messages are sent toward the source SPT.
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