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POICMP Checksum error
 

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  1. POICMP Checksum error
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    <p>I am trying to checksum icmp packet using the same technique for tcp and udp but it get wrong checksum, can you tell me where is my problem ?</p> <pre><code> ICMP_HEADER *icmpheader = new ICMP_HEADER; memcpy(icmpheader,ICMPHeader,sizeof(ICMP_HEADER)); icmpheader-&gt;Checksum = 0; PSEUDO_HEADER *psheader = new PSEUDO_HEADER; memcpy(&amp;psheader-&gt;daddr, &amp;IPHeader-&gt;DestinationAddress, sizeof(UINT)); memcpy(&amp;psheader-&gt;saddr, &amp;IPHeader-&gt;SourceAddress, sizeof(UINT)); psheader-&gt;protocol = IPHeader-&gt;Protocol; psheader-&gt;length = htons((USHORT)(sizeof(ICMP_HEADER) + ICMPDataSize)); psheader-&gt;zero = 0x0000; UINT packet_size = sizeof(ICMP_HEADER) + ICMPDataSize + sizeof(PSEUDO_HEADER); packet_size = packet_size + ((packet_size%2)*2); UCHAR *icmppacket = (UCHAR*)malloc(packet_size); memset(icmppacket,0, packet_size); memcpy(icmppacket, psheader, sizeof(PSEUDO_HEADER)); memcpy(&amp;icmppacket[sizeof(PSEUDO_HEADER)], icmpheader,sizeof(ICMP_HEADER)); memcpy(&amp;icmppacket[sizeof(PSEUDO_HEADER) + sizeof(ICMP_HEADER)],ICMPData,ICMPDataSize); if (GlobalChecksum((USHORT*)icmppacket,packet_size) != ICMPHeader-&gt;Checksum) { isMalformed = true; PacketError = PACKET_ICMP_CHECKSUM; } USHORT cPacket::GlobalChecksum(USHORT *buffer, UINT length) { register int sum = 0; USHORT answer = 0; register USHORT *w = buffer; register int nleft = length; while(nleft &gt; 1){ sum += *w++; nleft -= 2; } sum = (sum &gt;&gt; 16) + (sum &amp; 0xFFFF); sum += (sum &gt;&gt; 16); answer = ~sum; return(answer); } </code></pre>
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    1. USAnwar Mohamed
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      1. VTUpMod
    1. COShould you really reset `icmpheader->Checksum = 0` for the packet checksum? Afaik, it should only be cleared for the ICMP checksum (where the pseudo header is not included)
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      1. USJoachim Isaksson
    2. COYou can try with unsigned int sum, could be due to signed unsigned conversion. But there could be something else too.
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      1. USpraks411
 

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