Hi Kenneth, your description could be correct but it's confusing for some people. Switch as a L2 device doesn't care about ARP requests, only L3 devices process these requests.
Patrice Ngassam CEO NEN NET Inc. > Date: Tue, 8 Mar 2011 08:37:18 -0600 > From: [email protected] > To: [email protected] > CC: [email protected] > Subject: Re: [OSL | CCIE_RS] Arp Watch Flip Flops > > Kenneth, > > I believe you were correct, it was proxy-arp causing my issue. Thank you > very much for the help. > > -Marc > > On Wed, Mar 2, 2011 at 9:52 PM, Matlock, Kenneth L > <[email protected]>wrote: > > > What you may be seeing is a feature called 'proxy arp'. I'm not 100% sure > > of hte origins of it, but I know that in the real world it masks > > netmask/gateway problems on the clients. > > > > How? Well the switch sees an ARP request for something, and if it has a > > valid route to it, it sends out a proxy arp reply, with it's MAC instead. > > This allows the misconfigured client to send the packet as Layer2 to the > > switch, which can then route the packet. So if the client has a bad netmask > > or gateway, it will be ARPing for hosts that are not local, and the switch > > will 'fix' it. > > > > In practice I turn it off on all my boxes, because all it REALLY does for > > us is mask client issues, and fills up the ARP tables :) > > > > Ken > > > > ________________________________ > > > > From: [email protected] on behalf of marc abel > > Sent: Wed 3/2/2011 7:46 PM > > To: [email protected] > > Subject: [OSL | CCIE_RS] Arp Watch Flip Flops > > > > > > > > I hope you don't mind me asking a real world question here, I think the > > content is plenty relevant to the studies at hand. > > > > I have ARP watch running on my network and I am regularly seeing a flip > > flop > > occur from one of the hosts in a fairly new VLAN. Two 4506's have an > > interface in this VLAN with HSRP running between them. The host IP keeps > > flipping between the MAC of the laptop, and the MAC of the standby switch. > > This doesn't happen rapidly, but maybe a few times a day. To me this > > implies > > that the secondary switch is occasionally answering ARP query's for the > > host's IP address. Can anyone give an explanation or a theory of why the > > switch would do that? > > > > Thank you, > > > > Marc > > _______________________________________________ > > For more information regarding industry leading CCIE Lab training, please > > visit www.ipexpert.com > > > > > > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com
