Problem with ethernet

Derek Broughton news at
Thu May 10 15:19:11 UTC 2007

Michael S. Peek wrote:

> Steve Flynn wrote:
>> Are you really using ath0 for anything?
> That's the wireless interface.  

I imagine he knew that...

> When the wireless interface is on it 
> gets an IPv4 address.  When it's off, it gets this weird IPv6 address.

It doesn't _get_ this weird IP6 address. If you look at the HW address
you'll see that every IP6 address is related to the MAC address.  The idea
being that every interface should have a unique address on the internet,
eliminating the need for NAT and private subnets.

> I tried "ifdown ath0", but it said "ath0 not configured", so I used
> "ifconfig ath0 down" and that did the trick.

Indeed.  ifdown only works when the interface was initialled ifup'd, as
ifupdown maintains its own state table.
>> Turn it off and see if your problems go away...
> Nope, problem still there.
>> it looks like it's getting all of the traffic when you want to use
>> your wired network and I suspect you think data is leaving on eth0.
> Wasn't the routing table supposed to take care of that?

My (possibly erroneous) understanding of that is that you have to roll your
own if you want to be able to choose to route via different interfaces. 
It's not possible in a default install.

I think you need to turn off the wireless transmitter, remove the network
cable, ensure both interfaces are down, then insert the network cable and
watch what happens.

Since eth0 never got an IP address (it never even communicated to the DHCP
server - that's a zeroconfig address, I believe), just taking down the
wireless won't _make_ eth0 get an address.  You could run "dhclient eth0"
but unplugging and replugging the cable should do the job.

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