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300-410 Practice Question: In OSPFv3, what is the purpose of the link-local…
In OSPFv3, what is the purpose of the link-local address in the neighbor adjacency process?
⚠ Common exam trap
300-410 often tests the misconception that OSPFv3 uses global unicast addresses for neighbor adjacency, when in fact link-local addresses are used for all OSPFv3 control traffic and next-hop resolution.
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
✓
The link-local address is used as the source address for OSPFv3 packets and for next-hop resolution.
In OSPFv3, the link-local address (fe80::/10) is used as the source address for OSPFv3 packets and for next-hop resolution. OSPFv3 uses link-local addresses for neighbor discovery and adjacency formation, and all OSPFv3 control packets are sent from the link-local address. This is a key difference from OSPFv2, which uses the interface's global IPv4 address. The link-local address ensures that OSPFv3 operates independently of global unicast addressing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The link-local address is used as the router ID for OSPFv3.
Why it's wrong here
OSPFv3 uses a 32-bit router ID, not the 128-bit link-local address, which is scoped to a single link and cannot identify the router domain-wide. It tempts because link-local addresses do appear in OSPFv3 packets, but they serve next-hop and adjacency purposes, not router identification.
- ✓
The link-local address is used as the source address for OSPFv3 packets and for next-hop resolution.
Why this is correct
OSPFv3 runs over IPv6, so its packets use the interface link-local address as source, and that same address serves as the next-hop for routes learned across the link. This is the mechanism underpinning neighbour adjacency formation.
- ✗
The link-local address is only used for DR/BDR election.
Why it's wrong here
DR/BDR election on broadcast links uses interface priority and router ID, not the link-local address. It tempts because link-local addresses are exchanged in Hello packets during adjacency formation, but election outcomes depend on priority values and the 32-bit router ID instead.
- ✗
The link-local address is not used in OSPFv3; global unicast addresses are used instead.
Why it's wrong here
OSPFv3 relies on link-local addresses for Hello exchange, neighbour discovery and next-hop resolution; global unicast addresses are not required for adjacency formation. It tempts because OSPFv3 does support global addressing for other functions, but the adjacency process itself is built on link-local addressing.
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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