raw udp client port 50000 unreachable
^C[root@bogon raw-sockets-example]# cat raw_udp_client.c #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <signal.h> #include <errno.h> #include <linux/ip.h> #include <linux/udp.h> struct sockaddr_in *serveraddr = NULL, *clientaddr; int sockfd; #define PORT 50001 #define SERVER_PORT 50000 #define SERVER_ADDR "10.10.16.82" #define CLIENT_ADDR "10.10.16.81" /* structure to calculate UDP checksum * The below members are part of the IP header * which do not change from the UDP layer and hence * are used as a part of the UDP checksum */ struct pseudo_iphdr { unsigned int source_ip_addr; unsigned int dest_ip_addr; unsigned char fixed; unsigned char protocol; unsigned short udp_len; }; /* checksum code to calculate UDP checksum * Code taken from Unix network programming – Richard stevens*/ unsigned short in_cksum (uint16_t * addr, int len) { int nleft = len; unsigned int sum = 0; unsigned short *w = addr; unsigned short answer = 0; /* Our algorithm is simple, using a 32 bit accumulator (sum), we add * sequential 16 bit words to it, and at the end, fold back all the * carry bits from the top 16 bits into the lower 16 bits. */ while (nleft > 1) { sum += *w++; nleft -= 2; } /* mop up an odd byte, if necessary */ if (nleft == 1) { *(unsigned char *) (&answer) = * (unsigned char *) w; sum += answer; } /* add back carry outs from top 16 bits to low 16 bits */ sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */ sum += (sum >> 16); /* add carry */ answer = (unsigned short) ~sum; /* truncate to 16 bits */ return (answer); } /* Interrupt_handler – so that CTRL + C can be used to * exit the program */ void interrupt_handler (int signum) { close(sockfd); free(clientaddr); exit(0); } #if DEBUG /* print the IP and UDP headers */ void dumpmsg(unsigned char *recvbuffer, int length) { int count_per_length = 28, i = 0; for (i = 0; i < count_per_length; i++) { printf("%02x ", recvbuffer[i]); } printf("\n"); } #endif int main () { char buffer[1024] = {0}; unsigned char recvbuffer[1024] = {0}; int length; char *string = "Hello UDP server"; struct udphdr *udp_hdr = NULL; char *string_data = NULL; char *recv_string_data = NULL; char *csum_buffer = NULL; struct pseudo_iphdr csum_hdr; int error; signal (SIGINT, interrupt_handler); signal (SIGTERM, interrupt_handler); /* Part 1: create the socket */ sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_UDP); if(0 > sockfd) { printf("unable to create socket\n"); exit(0); } clientaddr = (struct sockaddr_in *)malloc(sizeof(struct sockaddr_in)); if (clientaddr == NULL) { printf("could not allocate memory\n"); goto end; } clientaddr->sin_family = AF_INET; clientaddr->sin_port = PORT; clientaddr->sin_addr.s_addr = inet_addr(CLIENT_ADDR); /* Part 2 – fill data structure and bind to socket */ if (0 != (bind(sockfd, (struct sockaddr *)clientaddr, sizeof(struct sockaddr_in)))) { printf("could not bind server socket to address\n"); goto end1; } /* part 3: read and write data */ serveraddr = (struct sockaddr_in *)malloc(sizeof(struct sockaddr_in)); if (serveraddr == NULL) { printf("Unable to allocate memory to server address socket\n"); goto end2; } serveraddr->sin_family = AF_INET; serveraddr->sin_port = SERVER_PORT; serveraddr->sin_addr.s_addr = inet_addr(SERVER_ADDR); error = connect(sockfd, (struct sockaddr *)serveraddr, sizeof(struct sockaddr_in)); if (error != 0) { printf("error %d", errno); printf("connect returned error\n"); goto end2; } /* copy the data after the UDP header */ string_data = (char *) (buffer + sizeof(struct udphdr)); strncpy(string_data, string, strlen(string)); /* Modify some parameters to send to client in UDP hdr */ udp_hdr = (struct udphdr *)buffer; udp_hdr->source = htons(PORT); udp_hdr->dest = htons(SERVER_PORT); udp_hdr->len = htons(sizeof(struct udphdr)); csum_buffer = (char *)calloc((sizeof(struct pseudo_iphdr) + sizeof(struct udphdr) + strlen(string_data)), sizeof(char)); if (csum_buffer == NULL) { printf("Unable to allocate csum buffer\n"); goto end1; } csum_hdr.source_ip_addr = inet_addr(CLIENT_ADDR); csum_hdr.dest_ip_addr = inet_addr(SERVER_ADDR); csum_hdr.fixed = 0; csum_hdr.protocol = IPPROTO_UDP; /* UDP protocol */ csum_hdr.udp_len = htons(sizeof(struct udphdr) + strlen(string_data) + 1); memcpy(csum_buffer, (char *)&csum_hdr, sizeof(struct pseudo_iphdr)); memcpy(csum_buffer + sizeof(struct pseudo_iphdr), buffer, (sizeof(struct udphdr) + strlen(string_data) + 1)); /* since we are resending the same packet over and over again * free the csum buffer here */ free (csum_buffer); while (1) { write(sockfd, buffer, sizeof(buffer)); memset(recvbuffer, 0, sizeof(recvbuffer)); read(sockfd, recvbuffer, sizeof(recvbuffer)); udp_hdr = (struct udphdr *)(recvbuffer + sizeof (struct iphdr)); recv_string_data = (char *) (recvbuffer + sizeof (struct iphdr) + sizeof (struct udphdr)); #if DEBUG dumpmsg((unsigned char *)&recvbuffer, (sizeof(struct iphdr) + sizeof(struct udphdr)+ strlen(string_data) + 1)); #endif if (PORT == ntohs(udp_hdr->dest)) { printf("udp packet received from port %d\n",ntohs(udp_hdr->source)); printf("data received from server is : %s\n", recv_string_data); } } end2: free(serveraddr); end1: free(clientaddr); end: close(sockfd); return 0; }
运行
Makefile rawsockets.c raw_udp_client raw_udp_server README.md sniffer sniffer3 sniffer.c
[root@bogon raw-sockets-example]# gcc raw_udp_client.c -o raw_udp_client
[root@bogon raw-sockets-example]# ./raw_udp_client
报文发出去了
ast login: Sun May 16 16:52:01 2021 from 10.10.16.1 [root@bogon ~]# tcpdump -i enahisic2i0 udp and host 10.10.16.82 -nnvvv tcpdump: listening on enahisic2i0, link-type EN10MB (Ethernet), capture size 262144 bytes 16:56:27.801833 IP (tos 0x0, ttl 64, id 34276, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0 16:56:27.802049 IP (tos 0x0, ttl 64, id 34277, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0 16:56:27.802145 IP (tos 0x0, ttl 64, id 34278, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0 16:56:27.802233 IP (tos 0x0, ttl 64, id 34279, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0 16:56:27.802314 IP (tos 0x0, ttl 64, id 34280, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0 16:56:27.802399 IP (tos 0x0, ttl 64, id 34281, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0 16:56:27.802490 IP (tos 0x0, ttl 64, id 34282, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0
收到端口不存在的icmp通知
tcpdump: listening on enahisic2i0, link-type EN10MB (Ethernet), capture size 262144 bytes 16:56:27.801999 IP (tos 0xc0, ttl 64, id 64114, offset 0, flags [none], proto ICMP (1), length 56) 10.10.16.82 > 10.10.16.81: ICMP 10.10.16.82 udp port 50000 unreachable, length 36 IP (tos 0x0, ttl 64, id 34276, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0 16:56:27.802112 IP (tos 0xc0, ttl 64, id 64115, offset 0, flags [none], proto ICMP (1), length 56) 10.10.16.82 > 10.10.16.81: ICMP 10.10.16.82 udp port 50000 unreachable, length 36 IP (tos 0x0, ttl 64, id 34277, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0 16:56:27.802204 IP (tos 0xc0, ttl 64, id 64116, offset 0, flags [none], proto ICMP (1), length 56) 10.10.16.82 > 10.10.16.81: ICMP 10.10.16.82 udp port 50000 unreachable, length 36 IP (tos 0x0, ttl 64, id 34278, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0 16:56:27.802290 IP (tos 0xc0, ttl 64, id 64117, offset 0, flags [none], proto ICMP (1), length 56) 10.10.16.82 > 10.10.16.81: ICMP 10.10.16.82 udp port 50000 unreachable, length 36 IP (tos 0x0, ttl 64, id 34279, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0 16:56:27.802371 IP (tos 0xc0, ttl 64, id 64118, offset 0, flags [none], proto ICMP (1), length 56) 10.10.16.82 > 10.10.16.81: ICMP 10.10.16.82 udp port 50000 unreachable, length 36 IP (tos 0x0, ttl 64, id 34280, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0 16:56:27.802463 IP (tos 0xc0, ttl 64, id 64119, offset 0, flags [none], proto ICMP (1), length 56) 10.10.16.82 > 10.10.16.81: ICMP 10.10.16.82 udp port 50000 unreachable, length 36 IP (tos 0x0, ttl 64, id 34281, offset 0, flags [DF], proto UDP (17), length 1044) 10.10.16.81.50001 > 10.10.16.82.50000: [no cksum] UDP, length 0
