Arp undo issue in all 2.4 and 2.6 kernel releases

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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,

Tim Wright
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