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Does ICMP packet contain TCP header

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I refer to the above question ( number 140 of kindle book (prep guide for WCNA exam)). The answer sheet in the same book says it does not contain TCP header. But I see in my packet capture some ICMP reply packets do contain TCP header. Can someone please explain?

THANKS

Vindra's avatar
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Vindra
asked 2018-03-16 06:26:29 +0000
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Generally: ICMP acts on top of IP, so ICMP packets don't contain their own(!) TCP header.

BUT the question is tricky in a sense that ICMP packets of some types (those ones reporting different problems, like in your trace - TTL exceeded, Destination unreachable etc.) according to RFC792 must contain some chunk of ORIGINAL datagram causing a problem.

In this case if original datagram used TCP, its TCP header will be present ICMP packet. It is not used for transport purposes though, but only for diagnostics purposes.

Packet_vlad's avatar
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Packet_vlad
answered 2018-03-16 07:46:01 +0000
cmaynard's avatar
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cmaynard
updated 2018-03-16 14:19:54 +0000
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Great explanation. Thanks

Vindra's avatar Vindra (2018-03-16 07:49:02 +0000) edit
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