title: Filtering encapsulated ipv6 packets with tcpdump
body: <p>I have IPv6 with Next header == 0x29(41). I want to filter packets by the destination address and port of IPv6/TCP frame inside the main IPv6 frame.</p>
  
  <p>tcpdump -B 1000000 -pnni any "ip6[6] == 0x29" </p>
  
  <pre><code>00:24:33.461496 IP6 xxxx &gt; yyyy: IP6 zzzz.45388 &gt; hhhh.443: Flags [.], ack 809205, win 2636, options [nop,nop,TS val 1395182923 ecr 142811329], length 0
  00:24:33.461505 IP6 xxxx &gt; yyyy: IP6 zzzz.45388 &gt; hhhh.443: Flags [.], ack 809205, win 2636, options [nop,nop,TS val 1395182923 ecr 142811329], length 0
  </code></pre>
  
  <p>Is it possible to do this with tcpdump? I can't find any information in pcap library documentation.</p>