title: tcpdump filter by ESP SPI value
body: <p>Does tcpdump support filtering by ESP traffic (proto 50) with a particular SPI value?</p>
  
  <p>It displays this value, so you would think this is possible!</p>
  
  <pre><code>21:15:23.143805 IP 64.7.134.1 &gt; 64.7.139.200: ESP(spi=0x0d8f42b8,seq=0x27)
  </code></pre>