Data ICMP error messages contain a data section that includes a copy of the entire IPv4 header, plus at least the first eight bytes of data from the IPv4 packet that caused the error message. The length of ICMP error messages should not exceed 576 bytes. This data is used by the host to match the message to the appropriate process. If a higher level protocol uses port numbers, they are assumed to be in the first eight bytes of the original datagram's data.
dAta icmp error MEssages cOnTain a daTa SectioN That iNCludeS A coPY OF The ENTire iPv4 heAder, pLUs At lEasT ThE FiRST eigHt bYtes oF dAta fROM tHE ipv4 pAcket thAT cAUsed the erroR messaGE. the lEngtH of Icmp eRroR messaGEs SHOulD nOT eXcEEd 576 BytEs. tHIs data iS used By tHE host To MaTch the mesSaGe to thE apprOpriAtE prOcesS. If A hIgHEr Level prOtOcol usES PORt NumbErS, They aRe AssUmED To Be in tHE First EiGht bytEs oF the orIgINAl daTaGram's datA