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300-410 Practice Question: Consider the following configuration on R5: !---…

Consider the following configuration on R5:

!--- R5 configuration

ip prefix-list PL-2 seq 5 permit 10.0.0.0/8 ge 16 le 24

! route-map RMAP permit 10 match ip address prefix-list PL-2 set community 100:100 !

router bgp 65200
 neighbor 192.168.1.2 route-map RMAP out

!

What is the effect of this configuration?

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

✓

Only routes with prefix 10.0.0.0/8 and mask length between 16 and 24 are sent to neighbor with community 100:100.

The prefix-list PL-2 permits prefixes that match 10.0.0.0/8 with a mask length greater than or equal to 16 and less than or equal to 24. So, for example, 10.1.0.0/16, 10.1.1.0/24 are permitted, but 10.0.0.0/8 itself (mask 8) is not. The route-map RMAP sets community 100:100 on matching routes. Routes that do not match the prefix-list are not processed by this route-map (since there is only one sequence), so they are denied (not sent to neighbor).

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • ✓

    Only routes with prefix 10.0.0.0/8 and mask length between 16 and 24 are sent to neighbor with community 100:100.

    Why this is correct

    Correct. The prefix-list permits 10.0.0.0/8 ge 16 le 24; matching routes get community set and are advertised.

  • ✗

    All routes with prefix 10.0.0.0/8 are sent to neighbor; routes with mask length between 16 and 24 get community 100:100.

    Why it's wrong here

    Incorrect. The prefix-list only permits routes with mask length 16-24; 10.0.0.0/8 itself is not permitted.

  • ✗

    Routes that match the prefix-list are sent with community 100:100; all other routes are sent without any community.

    Why it's wrong here

    Incorrect. Routes not matching the prefix-list are denied by the route-map because there is no catch-all permit.

  • ✗

    The configuration is invalid because the prefix-list uses ge and le together; only one can be used.

    Why it's wrong here

    Incorrect. Using both ge and le is valid; it specifies a range of prefix lengths.

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Same concept, more angles

1 more way this is tested on 300-410

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. Consider the following configuration on router R2: !--- R2 configuration ip prefix-list FILTER seq 5 deny 10.1.0.0/16 le 24 ip prefix-list FILTER seq 10 permit 0.0.0.0/0 le 32 ! route-map BGP-IN permit 10 match ip address prefix-list FILTER ! router bgp 65000 neighbor 192.168.1.1 route-map BGP-IN in ! What is the effect of this configuration?

medium
  • A.All routes from neighbor 192.168.1.1 are accepted; the prefix-list is not applied correctly because the route-map only has a permit sequence.
  • ✓ B.Routes within 10.1.0.0/16 with mask length 24 or shorter are denied; all other routes are permitted.
  • C.Only routes with mask length exactly 24 are denied; all other routes are permitted.
  • D.The configuration is incomplete; a route-map must have a deny statement to filter routes.

Why B: The prefix-list FILTER denies any prefix within 10.1.0.0/16 with a mask length less than or equal to 24 (i.e., 10.1.0.0/16 through 10.1.255.0/24). The permit statement allows all other prefixes. The route-map BGP-IN calls this prefix-list; since there is only one permit sequence, routes that match the deny statement in the prefix-list are implicitly denied by the route-map. Therefore, routes like 10.1.0.0/16, 10.1.1.0/24, etc., are filtered out.

JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.