350-401 Question 558
Single answerA network engineer is tasked with configuring an IPv6 traffic filter to block incoming ICMPv6 echo requests while allowing all other ICMPv6 traffic. Which configuration command should the engineer use on a Cisco router to meet this requirement?
- A
ipv6 access-list BLOCK_ICMP_ECHO permit icmp any any echo-reply
- B
ipv6 access-list BLOCK_ICMP_ECHO deny icmp any any echo-request
- C
ipv6 access-list BLOCK_ICMP_ECHO permit icmp any any
- D
ipv6 access-list BLOCK_ICMP_ECHO deny icmp any any echo-reply
Show answer and explanation
Correct answer: B
Explanation
To block ICMPv6 echo requests while allowing other ICMPv6 traffic, the correct access-list command is needed to explicitly deny echo-request traffic. In this case, 'ipv6 access-list BLOCK_ICMP_ECHO deny icmp any any echo-request' blocks echo requests while other ICMPv6 traffic is permitted, assuming the rest of the access list is configured correctly. This approach ensures that only echo requests are filtered without impacting other essential ICMPv6 functions.
- A. Incorrect.
This command permits ICMPv6 echo-reply traffic but does not block echo-request traffic, which is the primary requirement.
- B. Correct.
This command explicitly denies ICMPv6 echo requests, effectively blocking them as required, while allowing other ICMPv6 types (if the rest of the access list is configured correctly).
- C. Incorrect.
This command allows all ICMPv6 traffic, which does not meet the requirement to block ICMPv6 echo requests.
- D. Incorrect.
This command denies ICMPv6 echo-reply traffic, which is not part of the requirement. The task requires blocking echo requests, not echo replies.