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

  • Please tell us what system or platform you're asking about... Oct 1, 2014 at 13:05
  • @Mike Pennington Devices with BSD or Linux kernel. Also devices running IOS.
    – Martin
    Oct 1, 2014 at 13:14
  • Please ask on Server Fault for bsd or Linux questions. Cisco IOS is on-topic Oct 1, 2014 at 16:53
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    Aug 10, 2017 at 2:47

2 Answers 2


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.


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

  • 2
    Hi, that answer is a bit unspecific and you're only referencing links. Could you perhaps elaborate more so that the question has a meaningful answer? Oct 6, 2014 at 13:43
  • no, there's no sense to copy-paste docs. Answer it yourself.
    – poige
    Oct 6, 2014 at 19:05
  • 2
    @poige, SE prefers to not have answers that get the main content from links. The reason for this is that link dependent answers are subject to "link rot" and can result in answers that are no longer be useful to the community.
    – YLearn
    Oct 6, 2014 at 20:34
  • I hear this crap from time to time, but it's just crap. Do you really want to build your own internet (with blackjack and sluts) instead, which wouldn't rot? ;-P The whole idea behind Internet is hypertext, not copy-paste text.
    – poige
    Oct 7, 2014 at 3:06
  • 1
    @poige, perhaps you hear this from time to time because there is room to improve your answers. Please read shog9's question in meta.SE Oct 7, 2014 at 9:39

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