Another ARP message. Argh. ;-) I just wanted to tell you that my routers do what you describe too, i.e. send out ARPs for addresses that were in their ARP cache before you did "clear arp." This happens regardless of config, from what I can tell.
It's probably a good thing normally, as I'm sure you know. For example, if you replaced the NIC in a device the router had been talking to, the router would pick up the new MAC pretty quicly. But if you don't want it to happen there are some workarounds: 1. Do a shut on the interface. Then do a clear arp and a no shut. The router can't send its ARP requests if its interface is down. And it doesn't send them when you bring it back (until it needs to). 2. Disconnect a strategically-placed interface so devices can't respond to the ARP! _______________________________ Priscilla Oppenheimer www.troubleshootingnetworks.com www.priscilla.com 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. > > 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? > Thanks. > > Router#debug arp > ARP packet debugging is on > Router#show arp > Protocol Address Age (min) Hardware Addr Type > Interface > Internet 192.168.0.101 - 00d0.0b83.da30 ARPA > Ethernet0 > Internet 192.168.0.4 3 00d1.ab8a.3e8f ARPA > Ethernet0 > Internet 192.168.0.5 3 00e1.28a1.080d ARPA > Ethernet0 > Router#clear arp-cache > Router# > 02:32:33: IP ARP: sent req src 192.168.0.101 00d0.0b83.da30, > dst 192.168.0.4 00d1.ab8a.3e8f Ethernet0 > 02:32:33: IP ARP: sent req src 192.168.0.101 00d0.0b83.da30, > dst 192.168.0.5 00e1.28a1.080d Ethernet0 > 02:32:33: IP ARP: sent rep src 192.168.0.101 00d0.0b83.da30, > dst 192.168.0.101 ffff.ffff.ffff Ethernet0 > 02:32:33: IP ARP: rcvd rep src 192.168.0.4 00d1.ab8a.3e8f, dst > 192.168.0.101 > Ethernet0 > 02:32:33: IP ARP: creating entry for IP address: 192.168.0.4, > hw: > 00d1.ab8a.3e8f > 02:32:33: IP ARP: rcvd rep src 192.168.0.5 00e1.28a1.080d, dst > 192.168.0.101 > Ethernet0 > Router# > 02:32:33: IP ARP: creating entry for IP address: 192.168.0.5, > hw: > 00e1.28a1.080d > Router# > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=57063&t=56884 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
