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.
Are those IP addresses in your config somewhere, in static route entires, neighbor commands, or something of that sort? > > 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. It doesn't save bandwidth. The frame is the same size regardless of whether it's a broadcast or unicast. But it does avoid bothering other hosts. > > 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? Yes, it does this at startup too. I don't know if it's for security though. Maybe it's just making sure it's alive. Of course, it can do that with keepalives too, so it does seem sort of silly. It also broadcasts an ARP response with its own address in the Source and Target IP Address fields, and its own address in the Sender Hardware Address field, which is more understandable. That allows other hosts to add the mapping to their ARP cache. Priscilla > 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=56925&t=56884 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
