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Am I correct that only ARP request and ARP reply messages will update the Cisco IOS ARP cache?

Mike Pennington
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Martin
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2 Answers2

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I wouldn't say that ARP Requests / Replys are the only way an address makes it into the FIB, but it is certainly the most predominant. Gratutious ARP has been mentioned a few times, and with good reason. It doesn't follow the standard ARP Request/Reply procedures, but certainly accomplishes the same goal – populating the FIB with a relevant entry.

Don’t forget about manual intervention. Another way of populating the FIB is by manually setting a static address on the interface or having one automatically stick with port-security.

Community
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Ryan Foley
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In general — yeah. There's special case of ARP messages called Gratuitous ARP, but anyways there're either replies or requests.

https://learningnetwork.cisco.com/thread/16335 http://wiki.wireshark.org/Gratuitous_ARP

poige
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