[lug] physical/logical network interfaces

[Hugh Brown]

> > I have a disconnected nic named eth1.  I configure it.  Since there's no
> > cabled connected, I would expect that packets destined for it would fall
> > on the floor.
> >
> > Instead, what I'm seeing is eth0 is picking up all packets destined to
> > eth1 and the IP assigned to eth1 is associated with the MAC address for
> > eth0.
>
> No, the kernel is trying to be nice to you :-)
> What tool did you use to configure/set up your interfaces? 'ifconfig' or 'ip'?
> If you happen to have the 'ip' program installed, what does 'ip link list' show?

Indirectly it was the ip command that was used.  I had configured it with
the /etc/sysconfig/network-scripts/ifcfg-eth1 and then ran a service
network start (which calls the 'ip' command).

ip link list returns a list of all the interfaces with their correct MAC
addresses.


>
>
> > So what I think is "broken" is that eth0 has pre-empted eth1, not that I
> > was able to configure eth1 in the first place.
>
>
> I know, i've fallen into this trap myself (when i tried to have hosts connected
> by two cables with seperate networks on each cable. When i shut down one interface
> (assuming that i'd still have the other one to connect to the box i had
> to learn that that one interface was handling _all_ traffic ... and since our
> providers switch cached the arp entries itg wasn't too easy to get the system
> connected again).
> BTW, there _is_ some /proc fiddling to prevent all this IIRC ....
>

I think I'd rather feel the pain at set up time and have the kernel not be
nice to me.  Then when I had to drop an interface I wouldn't be dropping
all interfaces.

Any idea what the key name is or a good google keyword is for the /proc
twiddling?


Hugh