DHCPを含む2つのNIC（1つのバックアップとして使用）

次のバックグラウンドスクリプトを使用してこの問題を解決しました。

#!/bin/sh
PRIMARY=wlan0
SECONDARY=eth1
SLEEP=60
PING=8.8.8.8
CONDITION="100% packet loss"


while :
do
    echo Init
    ifmetric $PRIMARY 100
    ifmetric $SECONDARY 200
    if [ "`ip route | grep default | grep $PRIMARY`" = "" ];
    then
        ip route add default via `ip route show | grep $PRIMARY | grep "scope link" | sed 's/\(.*\)0\/.*/\1/'`1 dev $PRIMARY
    fi
    if [ "`ip route | grep default | grep $SECONDARY`" = "" ];
    then
        ip route add default via `ip route show | grep $SECONDARY | grep "scope link" | sed 's/\(.*\)0\/.*/\1/'`1 dev $SECONDARY
    fi
    ifmetric $PRIMARY 100
    ifmetric $SECONDARY 200
    echo Primary
    while [ "`ping -I $PRIMARY -c 10 -w 20 $PING | grep \"$CONDITION\"`" = "" ];
    do
        sleep $SLEEP
    done
    echo Secondary
    ifmetric $SECONDARY 50
    while [ -n "`ping -I $PRIMARY -c 10 -w 20 $PING | grep \"$CONDITION\"`" ];
    do
        ifdown $PRIMARY
        sleep $SLEEP
        ifup $PRIMARY
        sleep $SLEEP
    done
done