The answer is that the next-hop is not resolved for IPv6. In MP-BGP for IPv6, when OSPFv3 internal routes are redistributed into BGP, the next-hop address is typically set to the router’s own IPv6 address; however, if that address is a link-local address or is not present in the global IPv6 unicast routing table, iBGP peers cannot reach it and will not install or advertise the routes. This concept is frequently tested on the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, often as a trap where candidates assume redistribution alone is sufficient—overlooking that BGP requires a resolvable, global-scope next-hop for iBGP propagation. A common memory tip is “BGP won’t advertise what it can’t reach,” so always verify that the next-hop is both global and present in the routing table.
350-501 Networking Practice Question
This 350-501 practice question tests your understanding of networking. 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.
A service provider uses MP-BGP with IPv6 address family. They notice that routes redistributed from OSPFv3 are not being advertised to iBGP peers. The OSPF routes are internal. What is a likely reason?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The next-hop is not resolved for IPv6.
In MP-BGP for IPv6, the next-hop address for iBGP peers must be reachable via an IPv6 route in the global routing table or the appropriate VRF. When OSPFv3 redistributes internal routes into BGP, the next-hop is often set to the OSPFv3 router's own IPv6 address; if that address is not reachable (e.g., because the interface is not in the IPv6 unicast routing table or the next-hop is link-local), iBGP peers will not install the routes. This is a common cause of routes being learned but not advertised to iBGP peers.
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.
✗
The network command is missing under IPv6 address family.
Why it's wrong here
Network command is used for originating routes, not for redistribution.
✗
The bgp default ipv4-unicast command is disabled.
Why it's wrong here
This command affects IPv4 unicast address family activation, not IPv6.
✓
The next-hop is not resolved for IPv6.
Why this is correct
If the BGP next-hop for the redistributed routes is not reachable via the IPv6 routing table, BGP will not advertise them to iBGP peers.
Related concept
Read the scenario before looking for a memorised answer.
✗
The routes are not in the IPv6 unicast table.
Why it's wrong here
If redistributed, routes should be in the IPv6 table; this is not the common issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the issue is with the network command or the IPv4 unicast default, but the real problem is the IPv6 next-hop reachability, which is a subtle but critical requirement for MP-BGP IPv6 route propagation.
Trap categories for this question
Command / output trap
Network command is used for originating routes, not for redistribution.
Detailed technical explanation
How to think about this question
In MP-BGP, the next-hop for IPv6 routes must be a global unicast address that is reachable via the IPv6 routing table. When redistributing OSPFv3 routes, BGP may set the next-hop to the OSPFv3 router's own IPv6 address; if that address is a link-local address or is not in the global routing table, iBGP peers will reject the route because the next-hop is unresolved. This is often resolved by using the 'next-hop-self' command under the IPv6 address family or by ensuring the next-hop is a global unicast address that is reachable.
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: The next-hop is not resolved for IPv6. — In MP-BGP for IPv6, the next-hop address for iBGP peers must be reachable via an IPv6 route in the global routing table or the appropriate VRF. When OSPFv3 redistributes internal routes into BGP, the next-hop is often set to the OSPFv3 router's own IPv6 address; if that address is not reachable (e.g., because the interface is not in the IPv6 unicast routing table or the next-hop is link-local), iBGP peers will not install the routes. This is a common cause of routes being learned but not advertised to iBGP peers.
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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Question Discussion
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