The correct answer is to authenticate the LDP session using MD5. The 'mpls ldp neighbor ... password cisco' command enables Message Digest 5 (MD5) authentication on the TCP connection between two directly connected LDP peers, ensuring that only routers possessing the shared password can establish or maintain the session. This prevents spoofed or unauthorized Label Distribution Protocol messages from being accepted, a security requirement outlined in RFC 5036. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of LDP security mechanisms within the Service Provider core; a common trap is confusing this with MPLS TTL security or BGP authentication, but remember that LDP MD5 specifically protects the TCP transport layer, not the label exchange itself. A useful memory tip: “LDP needs a password to keep its TCP handshake from being hijacked” — think of it as a secret handshake for your MPLS control plane.
350-501 Networking Practice Question
This 350-501 practice question tests your understanding of networking. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Exhibit
Refer to the exhibit.
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.252
mpls ip
mpls mtu 1500
no shutdown
interface GigabitEthernet0/1
ip address 192.168.2.1 255.255.255.252
mpls ip
mpls mtu 1500
no shutdown
router ospf 1
network 192.168.1.0 0.0.0.3 area 0
network 192.168.2.0 0.0.0.3 area 0
mpls label protocol ldp
mpls ldp router-id Loopback0 force
mpls ldp neighbor 192.168.1.2 password cisco
mpls ldp neighbor 192.168.2.2 password cisco
Based on the exhibit, what is the purpose of the 'mpls ldp neighbor ... password cisco' commands?
Refer to the exhibit.
interface GigabitEthernet0/0
ip address 192.168.1.1 255.255.255.252
mpls ip
mpls mtu 1500
no shutdown
interface GigabitEthernet0/1
ip address 192.168.2.1 255.255.255.252
mpls ip
mpls mtu 1500
no shutdown
router ospf 1
network 192.168.1.0 0.0.0.3 area 0
network 192.168.2.0 0.0.0.3 area 0
mpls label protocol ldp
mpls ldp router-id Loopback0 force
mpls ldp neighbor 192.168.1.2 password cisco
mpls ldp neighbor 192.168.2.2 password cisco
A
To synchronize LDP and IGP convergence.
Why wrong: LDP-IGP synchronization is configured with 'mpls ldp igp sync'.
B
To control the label allocation for prefixes from that neighbor.
Why wrong: Label allocation is controlled by label policies, not authentication.
C
To authenticate the LDP session using MD5.
The password command enables MD5 authentication for the LDP session.
D
To enable LDP session protection for the neighbor.
Why wrong: Session protection is configured with a different command.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
To authenticate the LDP session using MD5.
The 'mpls ldp neighbor ... password cisco' command configures a Message Digest 5 (MD5) authentication password for the LDP session with a specific neighbor. This ensures that the TCP connection used for LDP exchanges is authenticated, preventing spoofed or unauthorized LDP messages from being accepted, as defined in RFC 5036.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
To synchronize LDP and IGP convergence.
Why it's wrong here
LDP-IGP synchronization is configured with 'mpls ldp igp sync'.
✗
To control the label allocation for prefixes from that neighbor.
Why it's wrong here
Label allocation is controlled by label policies, not authentication.
✓
To authenticate the LDP session using MD5.
Why this is correct
The password command enables MD5 authentication for the LDP session.
Related concept
Read the scenario before looking for a memorised answer.
✗
To enable LDP session protection for the neighbor.
Why it's wrong here
Session protection is configured with a different command.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between LDP authentication (password) and LDP session protection (holdtime/graceful restart), so the trap here is confusing the 'password' keyword with session protection features that maintain adjacency state.
Trap categories for this question
Command / output trap
Session protection is configured with a different command.
Detailed technical explanation
How to think about this question
Under the hood, the password is stored as a shared secret and used to compute an MD5 hash appended to each TCP segment of the LDP session, as specified in RFC 5036 and RFC 1321. A real-world scenario where this matters is in MPLS VPN provider networks, where an attacker could inject false label bindings to redirect traffic; MD5 authentication prevents such attacks by ensuring only trusted neighbors can establish LDP sessions.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: To authenticate the LDP session using MD5. — The 'mpls ldp neighbor ... password cisco' command configures a Message Digest 5 (MD5) authentication password for the LDP session with a specific neighbor. This ensures that the TCP connection used for LDP exchanges is authenticated, preventing spoofed or unauthorized LDP messages from being accepted, as defined in RFC 5036.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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