I found his explanation to be clear. I told him in the original question that I had 4506 switches which are obviously layer 3 capable.
I did however speak to soon, the problem seems to have re-presented itself today, after I have disabled proxy arp. -Marc On Tue, Mar 8, 2011 at 11:31 AM, Patrice Ngassam <[email protected]>wrote: > 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
