![]() ![]() //The source address is the one in the IPv6 header. IP HEADER PART PSEUDO HEADER(IT IS THAT PART WHICH LINK UDP OR PROTOCOL TO IPVX HEADER SO NAME AS PSEDUO HEADER IT IS OT REAL HEADER BUT MAKE LINK BTWN 2) SRC AND DSTN ADDRESS AND PROTOCOL AND LENTGH TO BE ADD WHICH WE HAVE TO EXTRACT FROM IP HEADER LENTFTH ABOVE IS 0X000C AND PROTOCOL OX11 Step 5) Calculate one's compliment of the 16-bit Sum CHECKSUM = 0x821A Xor 0xFFFF Step 4) Calculate 16-bit Sum from total (since it is > 0xFFFF) SUM_16BIT = 0x0002 + 0x8218 Step 3) Calculate Total SUM_TOTAL = SUM_PHDR + SUM_BODY The sum of your UDP section is: SUM_BODY = 0x2692 + 0x2692 +. Step 2) Calculate 16-bit sum of UDP Header + Data (excluding checksum) UDP Hdr : 26 92 26 92. The sum of your pseudo header is: SUM_PHDR = 0x2100 + 0x0000 +. The pseudo header contains Source IP, Destination IP, Protocol, UDP/TCP Length (header+body) Source IP: 21 00 00 00. Step 1) Calculate 16-bit sum of pseudo header. All numbers are represented in hexadecimal format. Steps for calculating the checksum (0x7ED5) in the UDP header. Your IPv6 Packet UDP Packet (in Hex format) 60 00 00 00. Printf( "selected source port number: %d \n ", ntohs(saddr.In case this question hasn't been answered yet, and for the benefit of others. if (getsockname(sock, (struct sockaddr*)&saddr, &addrLen) = -1) socklen_t addrLen = sizeof(struct sockaddr) if (bind(sock, (struct sockaddr*)&saddr, sizeof(struct sockaddr)) = -1) // call bind with port number specified as zero to get an unused source port Printf( "source IP configuration failed \n ") sin_port = htons( rand() % 65535) // random client port Printf( "destination IP configuration failed \n ") Int sock = socket(AF_INET, SOCK_RAW, IPPROTO_TCP) ĭaddr. Printf( "destination port: %d \n ", ntohs(dst-> sin_port)) ![]() Printf( "received bytes: %d \n ", received) Received = recvfrom(sock, buffer, buffer_length, 0, NULL, NULL) Int receive_from( int sock, char* buffer, size_t buffer_length, struct sockaddr_in *dst) Printf( "acknowledgement number: %lu \n ", ( unsigned long)*seq) Printf( "sequence number: %lu \n ", ( unsigned long)*seq) Void read_seq_and_ack( const char* packet, uint32_t* seq, uint32_t* ack) Memcpy(pseudogram + sizeof( struct pseudo_header), tcph, sizeof( struct tcphdr) + OPT_SIZE + data_len) Int psize = sizeof( struct pseudo_header) + sizeof( struct tcphdr) + OPT_SIZE + data_len tcp_length = htons( sizeof( struct tcphdr) + OPT_SIZE + data_len) Iph-> tot_len = sizeof( struct iphdr) + sizeof( struct tcphdr) + OPT_SIZE + data_len Void create_data_packet( struct sockaddr_in* src, struct sockaddr_in* dst, int32_t seq, int32_t ack_seq, char* data, int data_len, char** out_packet, int* out_packet_len)Ĭhar* payload = datagram + sizeof( struct iphdr) + sizeof( struct tcphdr) + OPT_SIZE Void create_ack_packet( struct sockaddr_in* src, struct sockaddr_in* dst, int32_t seq, int32_t ack_seq, char** out_packet, int* out_packet_len) Iph-> check = checksum(( const char*)datagram, iph-> tot_len) Tcph-> check = checksum(( const char*)pseudogram, psize) Memcpy(pseudogram + 34, &mss, sizeof( int16_t)) Memcpy(datagram + 42, &mss, sizeof( int16_t)) TCP options are only set in the SYN packet Memcpy(pseudogram + sizeof( struct pseudo_header), tcph, sizeof( struct tcphdr) + OPT_SIZE) Memcpy(pseudogram, ( char*)&psh, sizeof( struct pseudo_header)) Int psize = sizeof( struct pseudo_header) + sizeof( struct tcphdr) + OPT_SIZE tcp_length = htons( sizeof( struct tcphdr) + OPT_SIZE) TCP pseudo header for checksum calculation Tcph-> window = htons( 5840) // window size Tcph-> check = 0 // correct calculation follows later Iph-> check = 0 // correct calculation follows later Iph-> id = htonl( rand() % 65535) // id of this packet Iph-> tot_len = sizeof( struct iphdr) + sizeof( struct tcphdr) + OPT_SIZE Struct tcphdr *tcph = ( struct tcphdr*)(datagram + sizeof( struct iphdr)) Struct iphdr *iph = ( struct iphdr*)datagram required structs for IP and TCP header Void create_syn_packet( struct sockaddr_in* src, struct sockaddr_in* dst, char** out_packet, int* out_packet_len)Ĭhar *datagram = calloc(DATAGRAM_LEN, sizeof( char)) * Invert to get the negative in ones-complement arithmetic */ ![]() Unsigned short checksum( const char *buf, unsigned size)įor (i = 0 i > 16) sum = (sum & 0xFFFF)+(sum > 16) pseudo header needed for tcp header checksum calculation
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