Quick Answer
The correct answer is LDP and BGP, as these are the two protocols commonly used for MPLS label exchange. LDP, or Label Distribution Protocol, handles label distribution for Interior Gateway Protocol (IGP) routes, dynamically assigning labels to internal prefixes to build the core label-switched paths. BGP, on the other hand, is used to exchange VPN labels, enabling MPLS-based Layer 3 VPNs by carrying label information alongside route prefixes. On the Cisco SPCOR 350-501 exam, this question tests your understanding of which control plane protocols actually perform label binding versus those that simply route traffic; a common trap is mistaking OSPF or IS-IS for label exchange protocols, but these IGPs only provide routing information, not labels. PIM is also a distractor, as it manages multicast trees, not MPLS labels. A helpful memory tip: think of LDP for the local core labels and BGP for the border VPN labels—LDP inside, BGP outside.
This 350-501 practice question tests your understanding of architecture. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Which two protocols are commonly used for label exchange in an MPLS network? (Choose two.)
OSPF
Why wrong: OSPF does not exchange MPLS labels.
PIM
Why wrong: PIM is for multicast, not label exchange.
LDP
LDP exchanges labels for IGP prefixes.
BGP
BGP exchanges labels for VPN prefixes.
IS-IS
Why wrong: IS-IS does not exchange MPLS labels.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
LDP
LDP and BGP are commonly used for label exchange. LDP for IGP labels, BGP for VPN labels. OSPF, IS-IS, and PIM do not exchange MPLS labels.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
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 does not exchange MPLS labels.
PIM
Why it's wrong here
PIM is for multicast, not label exchange.
LDP
Why this is correct
LDP exchanges labels for IGP prefixes.
Related concept
OSPF neighbours must agree on key parameters.
BGP
IS-IS
Why it's wrong here
IS-IS does not exchange MPLS labels.
Common exam traps
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-501 OSPF questions on adjacency and route selection.
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FAQ
Architecture — This question tests Architecture — OSPF neighbours must agree on key parameters..
The correct answer is: LDP — LDP and BGP are commonly used for label exchange. LDP for IGP labels, BGP for VPN labels. OSPF, IS-IS, and PIM do not exchange MPLS labels.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-501 OSPF questions on adjacency and route selection.
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 24, 2026
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