But Im not even adding the sum to the checksum, and I get FFFF. Temp=z //copy bytes that correspond to # of bytes in the tcp header and dataĪrray.Copy(tcpHeader,0,tem p,12,tcpHe ader.Lengt h) //copy the tcp header inĪrray.Copy(data,0,temp,tcp Header.Len gth+12,dat a. Im having problems with IP Header checksum calculation. Temp=ipHeader //copy the protocol number out of the ip headerīyte z=BitConverter.GetBytes((u short)(tcp Header.Len gth+data.L ength)) Temp=ipHeader //cop y the dest ip bytes out of the ip Header into the temp Temp=ipHeader //cop y the source ip bytes out of the ipHeader to the temp So, as far as the algorithm goes, IP header checksum is : 16 bit one’s complement of the one’s complement sum of all 16 bit words in the header This means that if we divide the IP header is 16 bit words and sum each of them up and then finally do a one’s compliment of the sum then the value generated out of this operation would be the checksum. If(temp.Length%2!=0)//make sure the array is a multiple of 2 (b\c of the 16 bit word size) TcpHeader=0 //set the checksum field in the tcp header to 0īyte temp=new byte /*create the temp array for use when calculating the checksum*/ The next two bytes (B1E6) correspond to the IP header checksum of the packet, we'll calculate this 'manually. The next byte (06) correspond to the IP protocol field, which is set to 6, so the packet contains a TCP segment on it's payload. The IPv6 protocol does not use header checksums. It is carried in the IP packet header, and represents the 16-bit result of summation of the header words. TcpHeader and ipHeader are each 20 bytes(the length of each header without options)ĭata's length changes depending on the quanity of data being sent The next byte (40) correspond to the Time To Live field (TTL), which actually is 64 (4x161 + 0x160 64). The Internet checksum, also called the IPv4 header checksum is a checksum used in version 4 of the Internet Protocol (IPv4) to detect corruption in the header of IPv4 packets. TcpHeader, ipHeader, and data are all arrays of bytes The currently defined values of chksum are: 0 - TCP checksum 1 - 8-bit Fletcher's algorithm (see Appendix I) 2 - 16-bit Fletcher's algorithm (see Appendix II) Note that. with the alg im using now their being sent with incorrect checksums (according to ethereal). This option is not copied into each fragment, and appears only in the first fragment. Im trying to calculate tcp checksums for packets.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |