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I also changed the firewall settings so I can access the other servers in the network.
In /etc/sysctl.conf remove # in front of the line #net.ipv4.ip_forward=1
To take effect immediately: echo 1 > /proc/sys/net/ipv4/ip_forward
Then in /etc/security/packetfilter.d/50_local.sh add:
iptables -A FORWARD -i eth0 -o tun0 -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -s 10.173.175.0/24 -o eth0 -j ACCEPT
iptables -t nat -A POSTROUTING -s 10.173.175.0/24 -o eth0 -j MASQUERADE
and restart the firewall: /etc/init.d/univention-firewall restart
Works like a charm 