> I am not a network pro, therefor I ask you gladly for help. I have a
> gentoo box with 2 eth0 cards.

You don't. You have two Ethernet cards maybe.

> config_ppp0=("ppp")
> link_ppp0="eth1"
> plugins_ppp0=("pppoe")
> pppd_ppp0=(
>     "defaultroute"
>     "usepeerdns"
> )
> 
> username_ppp0="xxxx"
> password_ppp0="xxxx"
> 
> config_eth1=("85.183.112.3 broadcast 85.255.255.255 netmask 255.0.0.0")
> config_eth0=("192.168.1.1 broadcast 192.168.1.255 netmask 255.255.255.0")

The main problem here is: Your internet connection is on ppp0, not eth1. 
eth1 makes connection with your modem, so IP communication is not 
direct, rather tunneled (you don't need an IP configuration therefore on 
eth1).

config_eth1=("null")

Also remove the second config_ppp0 line, it overwrites your first one 
which you need ( config_ppp0=("ppp") ). You should get your IP address 
from your ISP even if it's static.