300-510 · Question #45
You have configured MSDP peering between two autonomous systems that pass traffic between two sites, but the peering has failed to come up. Which task do you perform to begin troubleshooting the probl
The correct answer is C. Verify that both source interfaces are reachable from both peers. MSDP (Multicast Source Discovery Protocol) uses TCP port 639 to establish peering sessions between Rendezvous Points (RPs) in different PIM-SM domains. Before investigating any protocol-level configuration, the most fundamental troubleshooting step is to confirm basic IP reachabi
Question
You have configured MSDP peering between two autonomous systems that pass traffic between two sites, but the peering has failed to come up. Which task do you perform to begin troubleshooting the problem?
Options
- AVerify that multicast has been disabled globally
- BVerify that PIM-DM is configured on the source interface
- CVerify that both source interfaces are reachable from both peers
- DVerify that the two MSDP peers allow asymmetric routing
How the community answered
(26 responses)- C96% (25)
- D4% (1)
Explanation
MSDP (Multicast Source Discovery Protocol) uses TCP port 639 to establish peering sessions between Rendezvous Points (RPs) in different PIM-SM domains. Before investigating any protocol-level configuration, the most fundamental troubleshooting step is to confirm basic IP reachability - that each peer's source interface is reachable from the other peer. Without this, the TCP session that MSDP relies on cannot be established. Option A is wrong because multicast must be enabled (not disabled) for MSDP to function. Option B is wrong because MSDP is used with PIM-SM, not PIM-DM. Option D is wrong because MSDP does not require asymmetric routing to be explicitly allowed - it simply needs reachability between peers.
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