title: Redhat Enterprise Linux 6 Multicast Feed
body: <p>I am writing an application which receives multicast data on a <strong>new</strong> Redhat Enterprise Linux 6 server. The support team gives me an application which is used for testing whether the server can get multicast data flow. </p>
  
  <p>Once I start the test application, and also having tcpdump running, 
  I can see the multicast data coming in, e.g., </p>
  
  <pre><code>12:58:21.645968 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 729
  12:58:21.648369 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 969
  12:58:21.649406 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 893
  12:58:21.651823 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 604
  12:58:21.654079 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 913
  12:58:21.656724 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 1320
  12:58:21.658194 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 124
  12:58:21.658226 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 217
  12:58:21.658348 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 182
  12:58:21.658625 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 1014
  12:58:21.659592 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 135
  12:58:21.659842 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 242
  12:58:21.660674 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 242
  12:58:21.660743 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 84
  12:58:21.662327 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 84
  12:58:21.669154 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 161
  12:58:21.669365 IP 10.26.12.22.50002 &gt; 238.6.6.36.50002: UDP, length 166
  12:58:21.670792 IP 10.26.12.22.60002 &gt; 238.230.230.100.60002: UDP, length 49
  12:58:21.670796 IP 10.26.12.22.60002 &gt; 238.230.230.100.60002: UDP, length 49
  12:58:21.670798 IP 10.26.12.22.60002 &gt; 238.230.230.100.60002: UDP, length 49
  12:58:21.670799 IP 10.26.12.22.60002 &gt; 238.230.230.100.60002: UDP, length 49
  </code></pre>
  
  <p>But the application is not able to pick up any data flow, i.e., the application runs as if the multicast data subscription is unsuccessful.</p>
  
  <p>The support team assures me that there is no problem with the test application, because it is running fine on other servers. Since I am having a <strong>new</strong> server, it is possible that some settings on the server are not right. </p>
  
  <p>I am wondering what Linux settings shall I look for which potentially may stop the application receiving the multicast data, even thought tcpdump can see the data. Missing libraries or packages?</p>
  
  <p>Thanks.</p>