UDP multicast client does not see UDP multicast traffic generated by tcpreplay

Question

I have two programs:

• server ... it generates UDP traffic on a chosen multicast
• listener ... it prints UDP traffic on a chosen multicast (it sub

Answer 1

We had the same problem. With tcpdump we saw the data; however, the multicast client/listener was not picking up the data. Then we realized that the Reverse Path Filter (rp_filter) was rejecting the packets.

After disabling the rp-filter, the client/listener application started picking up the packets. Use the below command to disable rp_filter:

echo 0 > /proc/sys/net/ipv4/conf/eth0/rp_filter

In the above, replace 'eth0' with the interface receiving the multicast if other than eth0