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I have two rpi's both of which have a wifi dongle. I can vnc into rpi but if I connect the two rpi's via Ethernet cable, vnc fails. Is there a way to hook the two rpi together via ethernet ports and retain access via wifi?

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    Note that although I think I have an answer to your problem of wifi dropping out when you plug in an ethernet cable, how to connect two computers directly with an ethernet cable is a different question (and off topic here). – goldilocks Feb 25 '15 at 16:57
  • I read somewhere that if you have wlan0 up then eth0 goes down. You need to search about what is going on there. I think there are some configs that need chaning – Piotr Kula Feb 26 '15 at 22:50
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Yes, put a static ip address for eth0 in /etc/network/interfaces on both RPis. The network has to be different than that of the WiFi devices.

  • This may be a simpler way of getting around ifplugd instigated events since it should prevent dropping DHCP on wifi. – goldilocks Feb 25 '15 at 16:59
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I'm guessing this is because of hijinks caused by ifplugd, which runs as an init service by default on raspbian. The intent is to configure ethernet automatically when a cable is plugged in, since this is an event that the normal NetworkManager system can't detect.

To test this premise, before you plug the cable into either pi, try and stop the service on both of them:

service ifplugd stop

Make sure it is really stopped with ps -C ifplugd (it shouldn't list anything). When I noticed this app on my first pi, it seemed very pesky and I had to completely uninstall it to prevent it from coming back.

Plug in the ethernet cable and see if the wifi goes down. If so, check ps -C ifplugd again (you'll need a keyboard and screen plugged in to debug this, obviously). If not, problem solved.

If the wifi goes down and ifplugd isn't running, you probably have to reconfigure or disable NetworkManager.

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