350-501 Architecture Practice Question
Which THREE protocols are used for label distribution in an MPLS network?
⚠ Common exam trap
Cisco often tests the distinction between routing protocols (OSPF, IS-IS) and label distribution protocols (LDP, RSVP, BGP), trapping candidates who assume that because a protocol is used in MPLS networks (e.g., OSPF for IGP), it also distributes labels.
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
✓
LDP
LDP (Label Distribution Protocol) is a standardized protocol (RFC 5036) specifically designed for label distribution in MPLS networks. It operates by discovering LDP peers and exchanging label mappings for each FEC (Forwarding Equivalence Class), enabling label-switched path (LSP) establishment without requiring a routing protocol to carry label information.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
OSPF
Why it's wrong here
OSPF is an IGP and does not distribute MPLS labels; it can advertise segment routing SIDs but not perform label distribution.
- ✓
LDP
Why this is correct
LDP is the most common label distribution protocol for MPLS.
- ✗
IS-IS
Why it's wrong here
IS-IS is an IGP and similarly does not distribute MPLS labels directly.
- ✓
BGP
Why this is correct
BGP is used for label distribution in MPLS VPN and inter-AS scenarios.
- ✓
RSVP
Why this is correct
RSVP-TE is used for label distribution in MPLS traffic engineering.
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