App cannot receive multicast packets on CentOS 7

I have a CentOS 7.2 machine that is a VMware guest. I am subscribing to a multicast group and seeing all the multicast I'd expect, but my app is not seeing the contents of the stream. strace shows that it is waiting on a select() system call. What am I forgetting?

Here's what I've done:

  • Started a multicast sender on a remote host.
  • Built a CentOS 7.2 guest on a VMware host.
  • I stop and disable firewalld, and yum erase filewalld on the guest. iptables -L shows:


Chain INPUT (policy ACCEPT) target     prot opt source               destination           Chain FORWARD (policy ACCEPT) target     prot opt source               destination           Chain OUTPUT (policy ACCEPT) target     prot opt source               destination          
  • I run : socat UDP4-RECVFROM:65000,ip-add-membership=,fork STDOUT
  • I see no output from the command.
  • netstat -gn shows that it is subscribed to the multicast group.
  • selinux is disabled, in /etc/selinux/config I see: SELINUX=disabled. Yes, I have rebooted since that setting. Also I see: SELinux status: disabled from sestatus
  • tcpdump -n -nn -i eth0 host shows packets hitting the interface from that IP, destined to the UDP port 65000.
  • Another host subscribed to the same multicast group sees data.
  • I build another VM guest, this time using CentOS 6.4, and it works fine. I see regular output from my multicast sender.
  • I build another VM guest, again using CentOS 7.2, and it works fine. This time I use a minimal install, however.

My issue looks like the firewall is blocking the packets, but as shown there is no firewall enabled.

The one significant difference between my not-working host and my working host is that the not-working host has two interfaces configured on it. But again, I am showing it as subscribed to the multicast group and I am showing packets hitting the interface. As well, I have shut down the second interface but that has not helped.



Category: linux Time: 2016-07-29 Views: 0

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