> -----Original Message----- > From: Stephen Hemminger [mailto:shemminger@xxxxxxxx] > Sent: Tuesday, November 28, 2006 12:29 PM > To: Tim Wright > Cc: linux-net@xxxxxxxxxxxxxxx; Tim Wright > Subject: Re: Arp undo issue in all 2.4 and 2.6 kernel releases > > On Tue, 28 Nov 2006 11:01:20 -0800 > "Tim Wright" <timw@xxxxxxxxxxxxx> wrote: > > > Hi folks, > > I have been tracking down a strange problem, and have a simple > > "reproduce-by" and was looking for opinions from those > better-versed > > in the networking code. Basically, it is possible to get a > system into > > a state where it responds to ARP requests even though no > interface has > > the address requested. Here is a simple reproduce-by: > > > > Select and address in the same subnet as eth0 # ifconfig eth0:5 > > W.X.Y.Z netmask ... up This works. Machine now responds to arp > > requests for W.X.Y.Z. > > # ifconfig eth0:6 W.X.Y.Z netmask ... up This fails as it > should. But, > > the damage is done. > > # ifconfig > > You will only see eth0 and eth0:5. There is no eth0:6 > interface. Good. > > # ifconfig eth0:5 down > > Now we are supposedly back to the original state. BUT the > machine will > > still respond to ARP requests for W.X.Y.Z > > > > The easiest way to get out of this is to bring up eth0:5 again, and > > bring it down again. However, this looks to me like the > undo code when > > a clashing address is found fails to clean up the arp side > of things > > correctly. Any clues here? > > > > Please copy me on any responses. I am not on the linux-net > mailing list. > > > > Thanks very much, > > This is a common confusion. Read the mailing list archives. > Linux associates IP address with system not interface, so it > will respond to ARP for any of the IP addresses on any interface. > Hi Stephen, At the point where the system is responding, there should be no interfaces with the given IP address and ifconfig confirms this. The IP address is not associated with any interface and should not be associated with the system either. The sequence of events is "bring up the address on one interface, try to bring it up on another alias, bring the address down". This isn't an issue of "replying to ARP out the wrong interface", it is replying to arp requests when no interfaces on the system have that IP address associated. Tim - To unsubscribe from this list: send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
