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Old 11-06-2016, 05:15 PM   #1
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DNS Issue - Trying to make a LiFi Router

I am trying to make a VLC/LiFi router using 2 beaglebones and additional circuitry. They are running a Debian based Linux. One is to act as the router for the other. It has an Ethernet cable connected to it which provides it an internet connection. They each have a VLC network interface which was developed and configured. They are on the same subnet. The router is and the client is I have setup the routing and forwarding so that all traffic from the eth0 port goes through vlc0. This is what I used to set it up:

echo "1" > sudo /proc/sys/net/ipv4/ip_forward
modprobe ip_tables
modprobe ip_conntrack
modprobe ip_conntrack_irc
modprobe ip_conntrack_ftp
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i vlc0 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i eth0 -o vlc0 -j ACCEPT
iptables -t nat -A PREROUTING -d -j DNAT --to-destination

On the client side I have setup as the default gateway so that all traffic goes out through the vlc0 interface.

With this setup I can ping any IP address without a problem but I cannot ping any urls like I have tried changing the information on the resolv.conf file on the client with various nameservers like and a local one that is used by the server. None of this has worked. The server works just fine pinging anything and browsing the web.

I did captures with Wireshark to see what packets are being sent and I see the DNS request being sent out but no reply.
Old 11-06-2016, 06:28 PM   #2
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Although it will not fix your DNS problem your rules are somewhat backwards.
With eth0 being your external network and vlc0 internal the rules should be:

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

iptables -A FORWARD -i eth0 -o vlc -m state --state RELATED,ESTABLISHED -j ACCEPT (only forwards traffic that has been initiated by your client)

iptables -A FORWARD -i vlc0 -o eth0 -j ACCEPT (forwards all traffic from your client to the external network)

With basic NAT the prerouting rule is not required. Your vlc0 subnet is but what is the eth0 subnet?
Old 11-07-2016, 04:35 PM   #3
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Thank you for your help. I wasn't 100% sure about the 2 forwarding rules. It worked just fine with just the Masquerade rule. I was trying everything I could to get it to work. The eth0 is on a different subnet. It depends on where I connect but its not the same the same as my vlc0 subnet.


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