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Old 11-06-2016, 05:15 PM   #1
jackie123
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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 192.168.0.1 and the client is 192.168.0.2. 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 192.168.0.1 -j DNAT --to-destination 192.168.0.2

On the client side I have 192.168.0.1 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 google.com. I have tried changing the information on the resolv.conf file on the client with various nameservers like 8.8.8.8 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
michaelk
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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 192.168.0.0/24 but what is the eth0 subnet?
 
Old 11-07-2016, 04:35 PM   #3
jackie123
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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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