350-501 Networking Practice Question
Which TWO of the following are characteristics of MPLS LDP?
⚠ Common exam trap
Cisco often tests the misconception that LDP requires an IGP for session reachability, but the trap is that LDP uses its own UDP discovery mechanism and can form sessions over any IP reachable path, though an IGP is commonly used for loopback reachability in practice.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Label distribution based on IP routing table
B is correct because MPLS LDP distributes labels for routes found in the IP routing table, not for BGP routes. LDP peers exchange label bindings for each prefix in the IGP routing table, enabling label-switched paths (LSPs) for those destinations. This is fundamental to LDP's operation as defined in RFC 5036.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Distributes labels for BGP routes
Why it's wrong here
LDP does not distribute labels for BGP routes unless specifically configured.
- ✓
Label distribution based on IP routing table
Why this is correct
By default, LDP distributes labels for all IGP routes.
- ✗
Requires an IGP like OSPF for session reachability
Why it's wrong here
LDP session can be established over any reachable IP, not solely IGP.
- ✓
UDP for discovery, TCP for session
Why this is correct
LDP uses UDP hellos and TCP for session establishment.
- ✗
TCP for both discovery and session
Why it's wrong here
LDP uses UDP for discovery.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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