[nSLUG] WiFi and ethernet too: how to make eth0 & wlan0 both work?

Dop Ganger nslug at fop.ns.ca
Fri Feb 24 10:16:11 AST 2017


On Fri, 24 Feb 2017, Mike Spencer wrote:

> Novel problem for me.
>
> I temporarily have my laptop talking to the internet via wireless on a
> cell phone set to act as an access point.  Works fine, using wicd.
>
> Now I would like to plug an ethernet cable into the laptop and also
> talk to my desktop via my own LAN router which is not connected to the
> internet, just to 3 local machines and a printer.
>
> But configuring eth0 with ethtool seems to cause wicd to drop the wifi
> connection.  I can only get the cabled connection to work by killing
> wicd.

I would hazard a guess that bringing eth0 up kicks off a dhcp client which 
receives a default gateway on your network and then overrides the default 
gateway provided by your phone. One way to work around this might be:

* Bring up your ethernet interface

* Check ifconfig and route -n to give you routing information. 0.0.0.0 is 
your default gateway. There should be a line giving your local network 
address (eg, 192.168.1.0), its netmask (eg, 255.255.255.0), and the 
interface it's associated with (eg, eth0).

* Look for the pid of the dhclient process with ps -aef | grep dhc

* Kill the dhclient process. May need to kill -9. The network 
configuration should still be in place. Delete the default gateway with 
route del default dev eth0

* Plug in your cell phone. The dhcp process generated should then give you 
a default route out.

At this point you should be able to hit all local IP addresses on your 
local network while using the cell phone for all other network access. 
Note that your DNS will be using your cell phone provider, so if you are 
using local DNS to give things on your network friendly names you probably 
will have to hit them by IP.

This Youtube video is not related to what I just said: 
https://www.youtube.com/watch?v=GE7QA1chUzw

Cheers... Dop.


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