Which feature can be used to reduce the number of ICMP unreachable message egressing a router?

3 thoughts on “Which feature can be used to reduce the number of ICMP unreachable message egressing a router?”

1. B

   ip icmp rate-limit unreachable [df] [ms] [log [packets] [interval-ms]]
   Example:
   Router(config)# ip icmp rate-limit unreachable df log 1100 12000

   Specifies the rate limitation of ICMP unreachable destination messages and the error message log threshold for generating a message. The default is no unreachable messages are sent more often than once every half second.
   The arguments and keywords are as follows:
   •df—(Optional) When Don’t Fragment (DF) bit is set in the ICMP header, a datagram cannot be fragmented. If the df keyword is not specified, all other types of destination unreachable messages are sent.
   •ms—(Optional) Interval at which unreachable messages are generated. The valid range is from 1 ms to 4294967295 ms.
   •log—(Optional) List of error messages. The arguments are as follows:
   –packets—(Optional) Number of packets that determine a threshold for generating a log. The default is 1000 packets.
   –interval-ms—(Optional) Time limit for an interval for which a logging message is triggered. The default is 60000 ms, which is 1 minute.
   Note Counting begins as soon as this command is configured.

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2. C

   http://www.ciscopress.com/articles/article.asp?p=345618&seqNum=5

   Starting in 12.0 of the Cisco IOS, Cisco implemented a default rate limit of one ICMP unreachable packet that a router would generate in a 500-millisecond (ms) interval. This prevents a router from responding to thousands of packets with unreachable destinations with a separate ICMP message for each of these access requests.

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   1. It´s trick because the question say “feature” not command. Therefore B is the correct one for me.

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