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I need to have a master Pi B+ and a slave Pi B+
Both will be running Tomcat
The master will have a wifi dongle, the slave will not
There IS NOT a router available
I need to be able to go to a web app on the master using wifi and the master needs to connect to the slave through ethernet. The master will go to a URL on the slave

I noticed when ever I plug in my ethernet cable the wifi ip disappears when I run ifconfig. So my problem is how to keep wifi and ethernet on at the same time and then how to connect one pi to another through ethernet

Can someone please explain to me how to do this

I will try what is explained here
http://raspberrypi.stackexchange.com/qu ... d-ethernet
Coping the post contents here


UPDATE: The working config files

I got it working right now so I'll share all my configuration files with the community. Firstly lets look at the wpa_supplicant.conf file:

pi@raspberrypi ~ $ sudo cat /etc/wpa_supplicant/wpa_supplicant.conf
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
ssid="****"
scan_ssid=1
proto=RSN
key_mgmt=WPA-PSK
pairwise=CCMP TKIP
group=CCMP TKIP
psk="****"
id_str="home"
priority=5
}
Next my new update interfaces file

pi@raspberrypi ~ $ sudo cat /etc/network/interfaces
auto lo
iface lo inet loopback

auto eth0
allow-hotplug eth0
iface eth0 inet static
address 192.168.1.101
netmask 255.255.255.0

auto wlan0
allow-hotplug wlan0
iface wlan0 inet static
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
address 192.168.0.157
netmask 255.255.255.0
broadcast 192.168.0.255
gateway 192.168.0.1

iface default inet dhcp
And now comes the tricky part, you have to disable the hotplugging of the eth0 device (else it will disable your wlan0). You do this by edting the following file:

pi@raspberrypi ~ $ sudo cat /etc/default/ifplugd
INTERFACES="eth0"
HOTPLUG_INTERFACES="eth0"
ARGS="-q -f -u0 -d10 -w -I"
SUSPEND_ACTION="stop"
I also have the following in my startup script, this will make sure my wifi does get started up (sometimes for no reason at all it would not start). You also have to kill the ifplugd daemon on the eth0 device:

pi@raspberrypi ~ $ sudo cat /etc/rc.local
#!/bin/sh -e

# Print the IP address
_IP=$(hostname -I) || true
if [ "$_IP" ]; then
printf "My IP address is %s\n" "$_IP"
fi

# Disable the ifplugd eth0
sudo ifplugd eth0 --kill
sudo ifup wlan0

exit 0
And that should work!