hardMultiple SelectObjective-mapped
300-410 Practice Question: An engineer is troubleshooting an EIGRP network…
An engineer is troubleshooting an EIGRP network where some routers are not learning all routes, and suspects a route filtering issue. Which TWO statements about EIGRP route filtering are true? (Choose TWO.)
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
✓
A distribute-list configured under the EIGRP process using an ACL will filter routes based on the source IP address of the EIGRP update, not the route prefix.
A is correct because a distribute-list using an ACL matches the source IP of the EIGRP update, not the route prefix. B is correct because a prefix-list can use ge and le operators to match both prefix and prefix length. C is false because an outbound distribute-list filters routes before sending to neighbors, not local installation. D is false because an interface-specific distribute-list takes precedence over a process-level one. E is false because the distance command sets administrative distance; while a value of 255 prevents route installation, it is not considered a route filtering method in the context of EIGRP distribute-lists. Thus, only A and B are true.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A distribute-list configured under the EIGRP process using an ACL will filter routes based on the source IP address of the EIGRP update, not the route prefix.
Why this is correct
When using an ACL in a distribute-list under EIGRP, the ACL matches the source IP address of the router sending the update, not the route prefix itself. This is a common misconception.
- ✓
A prefix-list applied in a distribute-list under EIGRP can filter routes based on both the prefix and the prefix length, using ge and le operators.
Why this is correct
Prefix-lists allow granular matching of prefix and prefix length using 'ge' (greater than or equal) and 'le' (less than or equal) operators, making them more flexible than ACLs for route filtering.
- ✗
An outbound distribute-list on an EIGRP router will prevent the router from installing filtered routes in its own routing table.
Why it's wrong here
An outbound distribute-list filters routes being sent to neighbors; it does not affect the local router's routing table. Inbound distribute-lists filter routes being received and installed.
- ✗
If a distribute-list is applied both at the EIGRP process level and on a specific interface, the process-level distribute-list takes precedence for that interface.
Why it's wrong here
Interface-specific distribute-lists override the process-level distribute-list for that interface. The more specific configuration takes precedence.
- ✗
The 'distance' command configured under EIGRP can be used to filter routes by setting the administrative distance to 255, which prevents the route from being installed.
Why it's wrong here
Setting the administrative distance to 255 effectively filters the route because routes with AD 255 are not installed in the routing table. This is a valid method to filter routes.
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.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
Key term
ACL for Routing Protocols
An ACL for Routing Protocols is a set of rules used to filter routing updates between routers, controlling which network routes are advertised or accepted to improve security and stability.
Key term
BGP Prefix Filtering
BGP Prefix Filtering is the practice of controlling which network routes (prefixes) a router accepts or advertises to its BGP neighbors, preventing unwanted or harmful routes from spreading across the internet.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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