Marty Adkins wrote: > The "clear arp" command has always been a misnomer. It more > properly > should be "refresh arp" because that's what it does.
That's a good way of looking at it. > 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. What it sends already is a reply, as the debug in the original message stated. Here's an example: Ethernet Header Destination: FF:FF:FF:FF:FF:FF Ethernet Broadcast Source: 00:00:0C:05:3E:80 Protocol Type: 0x0806 IP ARP ARP - Address Resolution Protocol Hardware: 1 Ethernet (10Mb) Protocol: 0x0800 IP Hardware Address Length:6 Protocol Address Length:4 Operation: 2 ARP Response Sender Hardware Address:00:00:0C:05:3E:80 Sender Internet Address:10.10.0.1 Target Hardware Address:FF:FF:FF:FF:FF:FF Ethernet Broadcast Target Internet Address:10.10.0.1 This should hopefully put an entry in the recipeints' ARP caches, as I mentioned. I think that's its goal. As far as helping the router determine if there's a dupliate IP address, maybe it would trigger a host with that address to send an ARP request or something, but I don't think that's what it's attempting to do. >From my testing, the router doesn't do what you would expect it to do to determine if someone else is using its own address, i.e. broadcast an ARP Request with its own address in the Target Internet Address field. It does, by the way, send itself an ARP reply, in addition to the broadcast ARP reply above. Ethernet Header Destination: 00:00:0C:05:3E:80 Source: 00:00:0C:05:3E:80 Protocol Type: 0x0806 IP ARP ARP - Address Resolution Protocol Hardware: 1 Ethernet (10Mb) Protocol: 0x0800 IP Hardware Address Length:6 Protocol Address Length:4 Operation: 1 ARP Request Sender Hardware Address:00:00:0C:05:3E:80 Sender Internet Address:10.10.0.1 Target Hardware Address:00:00:0C:05:3E:80 Target Internet Address:10.10.0.1 _______________________________ Priscilla Oppenheimer www.troubleshootingnetworks.com www.priscilla.com > 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=57136&t=56884 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
