IP Forwarding and Enable UDP Multicast

During few days, I am confused on steaming of live TV that I created on our product. I couldn't forward the streaming of live tv on UDP multicast from eth0 to eth1. Our server has 2 network interface card and let say eth0 with IP 10.10.10.5 and eth1 with IP 172.31.16.26. In my opinion, it should be easy to be done but unfortunately, it is not simple as i thought. In order to make this happen then i created some simple experiment to forward traffic from eth0 to eth1. Here is my step to implement the things on how to forward IP and Port.

Step 1. Make sure the ip_forward is enable. Check on /etc/sysctl.conf and change the value to net.ipv4.ip_forward=1  If the flag is commented then just uncomment the line by removing # or you can do by typing on terminal sudo sysctl -w net.ipv4.ip_forward=1

Step 2. Change net.ipv4.conf.default.rp_filter=1. Check on /proc/sys/net/ipv4/conf/eth0/rp_filter and change the value to net.ipv4.conf.default.rp_filter=2


Step 3. Type this command on terminal 

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
This command can be explained in the following way:
iptables: the command line utility for configuring the kernel
-t nat: select table "nat" for configuration of NAT rules.
-A POSTROUTING:  Append a rule to the POSTROUTING chain (-A stands for "append").
-o eth0: this rule is valid for packets that leave on the second network interface (-o stands for "output")
-j MASQUERADE: the action that should take place is to 'masquerade' packets, i.e. replacing the sender's address by the router's address.

Then forward packet from eth0 to eth1 

sudo iptables -A FORWARD -i eth0 -o eth1 -m state --state RELATED,ESTABLISHED -j ACCEPT

sudo iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT

Step 4. Add route to enable UDP multicast address from 224.0.0.0 to 239.255.255.255
route add -net 224.0.0.0 netmask 240.0.0.0 dev eth0

Step 5. Make sure your firewall is inactive or if firewall enable then you must change DEFAULT_INPUT_POLICY="ACCEPT" on /etc/default/ufw 

Step 6. To check if the things is working properly then send data over UDP  by typing command on terminal 

echo "This is my data" > /dev/udp/239.255.0.1/3000

This will send text "This is my data" to UDP with IP 239.255.0.1 and Port 3000 and 

from the other terminal, just dump by typing command 

tcpdump -i eth1 udp port 3000 -vv -X

If you are successfully, then you will receive the text

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