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300-410 Practice Question: Configures BGP synchronization on an iBGP router
A network engineer configures BGP synchronization on an iBGP router. The IGP (OSPF) does not carry the BGP routes. Unexpectedly, the router does not advertise these iBGP routes to eBGP neighbors. What is the most likely explanation?
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 router has 'bgp synchronization' enabled, and the iBGP route is not in the OSPF routing table, so it is not considered valid for advertisement.
BGP synchronization requires that an iBGP route must be present in the IGP before it can be advertised to eBGP neighbors. If the IGP does not carry the route, the router will not advertise it, even if it is in the BGP table.
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 router has 'bgp synchronization' enabled, and the iBGP route is not in the OSPF routing table, so it is not considered valid for advertisement.
Why this is correct
With synchronization enabled, the router checks the IGP for the prefix. If missing, the route is not advertised to eBGP.
- ✗
The router has 'bgp bestpath as-path multipath-relax' configured, which suppresses eBGP advertisements for iBGP routes.
Why it's wrong here
This command affects multipath, not synchronization or advertisement.
- ✗
The iBGP session is not using 'next-hop-self', so the next hop is unreachable.
Why it's wrong here
Next-hop-self affects reachability, but synchronization is a separate check.
- ✗
The router has 'bgp suppress-duplicates' enabled, which drops identical routes.
Why it's wrong here
This is not a valid BGP command.
Visual reference
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 by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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