300-420 Question 121
Single answerAn enterprise network has multiple branch offices connected to the headquarters via OSPF. Each branch office has a range of subnets in the 192.168.x.0/24 space. The network engineer wants to reduce the size of the OSPF routing table at the headquarters by implementing route summarization on the branch routers. Which of the following summarized route advertisements would be appropriate for the branch router to advertise to the headquarters, assuming the branch subnets are 192.168.16.0/24 through 192.168.31.0/24?
- A
192.168.0.0/16
- B
192.168.16.0/20
- C
192.168.16.0/19
- D
192.168.0.0/18
Show answer and explanation
Correct answer: C
Explanation
To reduce the size of the OSPF routing table, route summarization allows advertising a single route that encompasses a range of subnets. The subnets 192.168.16.0/24 through 192.168.31.0/24 fall within the range of 192.168.16.0/19. This summarization ensures efficient routing without including unnecessary subnets, making 192.168.16.0/19 the correct choice.
- A. Incorrect.
192.168.0.0/16 is overly broad and would include subnets outside the range of 192.168.16.0/24 through 192.168.31.0/24, leading to incorrect routing.
- B. Incorrect.
192.168.16.0/20 is too narrow and would not include all the subnets from 192.168.16.0/24 through 192.168.31.0/24. It only covers 192.168.16.0/24 to 192.168.31.0/24.
- C. Correct.
192.168.16.0/19 is the correct summarization as it encompasses all subnets from 192.168.16.0/24 through 192.168.31.0/24 without including unnecessary subnets.
- D. Incorrect.
192.168.0.0/18 is overly broad and would include subnets outside the intended range, leading to inefficient routing.