Cable Guy wrote: > > I am trying to clear arp-cache in IOS 12.1 and get unexpected results. Below > you see debug arp turned on, the current arp cache, then the clear command. > Immediately, the router sends out arp requests for the entries that were in > the cache. > > Why does the router immediately send arp requests when I attempt to clear > the cache? I would think it would wait till a need arose to send the > appropriate arp request, afterall, I do want to clear the cache? Is there > some way to prevent this? > > Further, looking at the debug #1 and 2, why is the arp request being sent > with target MAC address? This is more confusing. Why bother arping if it > knows the target MAC address? I can only think Cisco is saving some > bandwidth here. > The "clear arp" command has always been a misnomer. It more properly should be "refresh arp" because that's what it does. That's why it unicasts the ARP requests, to check if they're still valid, if the target is still there.
> And a bigger question, why is the router sending itself an ARP...packet > number 3 below. Is it some sort of security measure? Does it do this at > startup too? The router is testing for a duplicate IP address. Hopes it doesn't get a reply. Yes, it does that any time the interface changes state to up, or the IP is changed. The only way I know to truly clear the arp entries associated with an interface is to shut/no shut that interface. - Marty Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=57107&t=56884 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
