On Fri, 16 Dec 2005, I wrote:
> Is it expected behavior that ARP replies would be generated for interfaces
> on a different network than the IP address in the ARP request (note I
> don't have Proxy ARP enabled), or is this a bug? To me it would seem
> to be a bug.
Answering my own question for the benefit of anyone else who might
encounter this odd behavior. I put the following entry into my
/etc/sysctl.conf file:
net.ipv4.conf.all.arp_ignore = 1
I was not familiar with this setting before, and happened to be led
to it by examining the arp.c source code.
Now everything works as expected. It still seems strange to me that
this is not the default behavior.
Now that I know about it, here's the info from
Documentation/networking/ip-sysctl.txt:
arp_ignore - INTEGER
Define different modes for sending replies in response to
received ARP requests that resolve local target IP addresses:
0 - (default): reply for any local target IP address, configured
on any interface
1 - reply only if the target IP address is local address
configured on the incoming interface
2 - reply only if the target IP address is local address
configured on the incoming interface and both with the
sender's IP address are part from same subnet on this interface
3 - do not reply for local addresses configured with scope host,
only resolutions for global and link addresses are replied
4-7 - reserved
8 - do not reply for all local addresses
The max value from conf/{all,interface}/arp_ignore is used
when ARP request is received on the {interface}
-Bill
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