Quick Answer
The answer is that the LDP session is operational with peer 10.0.0.5. This conclusion is drawn directly from the output of the `show mpls ldp neighbor vrf CUSTOMER-C` command, which displays a State of "Oper" and an Up time of 02:30:00, confirming that the Label Distribution Protocol adjacency is fully established and exchanging labels within the specified VRF. On the ENCOR 350-401 exam, verifying an LDP session in a VRF context tests your ability to differentiate between a control-plane protocol state and the underlying data-plane forwarding; a common trap is confusing the discovery source IP (10.0.1.2) with the peer LDP router ID (10.0.0.5), but the key is that the LDP Ident and TCP connection on port 646 define the session. Remember the memory tip: "Oper is the goal, not the hello"—the operational state, not the hello adjacency, confirms the LDP session is truly up.
This 350-401 practice question tests your understanding of vrf and path isolation. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A network engineer runs the following command on Router R4:
R4# show mpls ldp neighbor vrf CUSTOMER-C
Peer LDP Ident: 10.0.0.5:0; Local LDP Ident 10.0.0.4:0 TCP connection: 10.0.0.5.646 - 10.0.0.4.646 State: Oper; Msgs sent/rcvd: 500/500; Downstream Up time: 02:30:00 LDP discovery sources: GigabitEthernet0/0.300, Src IP addr: 10.0.1.2 hello sent/rcvd: 1000/1000 Addresses bound to peer LDP Ident:
10.0.1.2 10.0.2.2
Based on this output, what can be concluded?
LDP is not configured for VRF CUSTOMER-C
Why wrong: The command shows a neighbor, so LDP is configured.
The LDP session is operational with peer 10.0.0.5
State is 'Oper' (operational), indicating the session is up.
The LDP session is using TCP port 179
Why wrong: LDP uses TCP port 646, not 179.
The peer is discovered via OSPF
Why wrong: Discovery is via hello messages on GigabitEthernet0/0.300, not OSPF.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The LDP session is operational with peer 10.0.0.5
The output shows 'State: Oper' and 'Up time: 02:30:00', which confirms the LDP session is fully operational. The peer LDP Ident is 10.0.0.5:0 and the local LDP Ident is 10.0.0.4:0, with a TCP connection established on port 646. This directly indicates that the LDP session with peer 10.0.0.5 is up and running.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
LDP is not configured for VRF CUSTOMER-C
Why it's wrong here
The command shows a neighbor, so LDP is configured.
The LDP session is operational with peer 10.0.0.5
Why this is correct
State is 'Oper' (operational), indicating the session is up.
Related concept
Read the scenario before looking for a memorised answer.
The LDP session is using TCP port 179
Why it's wrong here
LDP uses TCP port 646, not 179.
The peer is discovered via OSPF
Why it's wrong here
Discovery is via hello messages on GigabitEthernet0/0.300, not OSPF.
Common exam traps
Cisco often tests the distinction between LDP (TCP port 646) and BGP (TCP port 179), and candidates may confuse the 'Oper' state with a BGP session or assume LDP uses port 179 by default.
Trap categories for this question
Command / output trap
The command shows a neighbor, so LDP is configured.
Detailed technical explanation
LDP uses TCP port 646 to establish a session between LDP peers, and the 'State: Oper' indicates the session is in the Operational state per RFC 5036. The 'Downstream' label indicates the label advertisement mode, which is the default for Cisco IOS. In MPLS VPN environments, LDP must be configured per VRF to exchange labels for VPN routes, and the 'show mpls ldp neighbor vrf' command verifies that the LDP session is specific to that VRF instance.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
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FAQ
VRF and Path Isolation — This question tests VRF and Path Isolation — Read the scenario before looking for a memorised answer..
The correct answer is: The LDP session is operational with peer 10.0.0.5 — The output shows 'State: Oper' and 'Up time: 02:30:00', which confirms the LDP session is fully operational. The peer LDP Ident is 10.0.0.5:0 and the local LDP Ident is 10.0.0.4:0, with a TCP connection established on port 646. This directly indicates that the LDP session with peer 10.0.0.5 is up and running.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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