350-501 Networking Practice Question
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?
⚠ Common exam trap
A common mix-up: candidates 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.
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 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.
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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