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I am relatively new to dealing with network packets, but as I look into the ipv6 header formats, I do not see a place where the ipv6 headers define what protocol is used in the data section -- but the ipv4 protocol does.

Am I missing where ipv6 gives the protocol information, or is that information no longer deemed necessary?

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2 Answers 2

It turns out that the "Next Header" field in IPv6 does the same thing as the "Protocol" field does in IPv4. See http://en.wikipedia.org/wiki/List_of_IP_protocol_numbers .

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The version (= 6) in IPv6 is located in the exact same place in the packet that it is in IPv4: the first 4 bits. That way, you can read the first 4 bits of the packet and find out which version of IP the packet is without knowing in advance.

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That's not quite the field I was talking about. I'm not talking about which version of the IP protocol being used. In IPv4 there is a "protocol" field at byte 9. For example, it could be the value of 6 which would mean that the data itself is using TCP. –  Alexander Bird Jun 14 '13 at 17:04
    
I see what you were looking for now, but this Answer is correct given what the Question seems to be asking for... –  Chris S Jun 14 '13 at 19:05
    
Ah yes, I see I misunderstood what you were asking! But yeah, you seem to have got the answer you were looking for, regarding the next header field. –  Celada Jun 14 '13 at 20:03

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