Tehát a helyes megoldás kb. így nézne ki:
iptable -t mangle -A OUTPUT -m state --state new -j MARK --set-mark 1
iptable -t mangle -A OUTPUT -m state --state new -j MARK --set-mark 2 -m statistic --mode random --probability 0.5
ip route add default via $ETH_GW table eth
ip route add default dev ppp0 table ppp
ip rule add from $ETH_IP table eth
ip rule add from $PPP_IP table ppp
ip rule add fwmark 1 table eth
ip rule add fwmark 2 table ppp