linux. Routing with 3g and wifi connection

Question

linux

Hello.
There is a server on Debian, a 3g modem is plugged into it and it is connected to the network via wi-fi, which periodically falls off.
The task is as follows: if there is a wi-f connection, drive all traffic through it, if the connection has fallen off, drive traffic through 3g.
Now when a 3g connection appears, all traffic goes through it. (((
I have a feeling that it's easy enough to achieve what you want, but google doesn't work.
Output netstat -n -r
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
0.0.0.0 10.64.64.64 0.0.0.0 UG 0 0 0 ppp0
10.64.64.64 0.0.0.0 255.255.255.255 UH 0 0 0 ppp0
192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 wlan0
192.168.66.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0

Answer 1

https://code.google.com/p/wanfailoverscript/ see something like that.
In general, look for something on the request "linux failover WAN".

Answer 2

habrahabr.ru/post/30076 - isn't it?