是否可以在IP协议下使用ICMP套接字?也许是这样的:
socket(PF_INET, <type>, IPPROTO_ICMP)?
我应该把什么放在&lt;类型&gt;领域?我看到了一些使用SOCK_RAW的例子,但这不会阻止操作系统处理IP协议的工作吗?
另一件事。操作系统如何知道他应该向哪个进程发送ICMP数据报,因为该协议没有涉及端口?
答案 0 :(得分:20)
Linux有一个特殊的ICMP套接字类型可以用于:
socket(PF_INET, SOCK_DGRAM IPPROTO_ICMP);
这允许您只发送ICMP回应请求内核将专门处理它(匹配请求/响应,填写校验和)。
仅在设置了special sysctl时才有效。默认情况下,甚至root都不能使用这种套接字。您可以指定可以访问它的用户组。要允许root(组0)使用ICMP套接字,请执行:
sysctl -w net.ipv4.ping_group_range="0 0"
这是一个示例程序,用于演示发送ICMP回应请求的基本用法:
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip_icmp.h>
#include <arpa/inet.h>
#include <sys/select.h>
//note, to allow root to use icmp sockets, run:
//sysctl -w net.ipv4.ping_group_range="0 0"
void ping_it(struct in_addr *dst)
{
struct icmphdr icmp_hdr;
struct sockaddr_in addr;
int sequence = 0;
int sock = socket(AF_INET,SOCK_DGRAM,IPPROTO_ICMP);
if (sock < 0) {
perror("socket");
return ;
}
memset(&addr, 0, sizeof addr);
addr.sin_family = AF_INET;
addr.sin_addr = *dst;
memset(&icmp_hdr, 0, sizeof icmp_hdr);
icmp_hdr.type = ICMP_ECHO;
icmp_hdr.un.echo.id = 1234;//arbitrary id
for (;;) {
unsigned char data[2048];
int rc;
struct timeval timeout = {3, 0}; //wait max 3 seconds for a reply
fd_set read_set;
socklen_t slen;
struct icmphdr rcv_hdr;
icmp_hdr.un.echo.sequence = sequence++;
memcpy(data, &icmp_hdr, sizeof icmp_hdr);
memcpy(data + sizeof icmp_hdr, "hello", 5); //icmp payload
rc = sendto(sock, data, sizeof icmp_hdr + 5,
0, (struct sockaddr*)&addr, sizeof addr);
if (rc <= 0) {
perror("Sendto");
break;
}
puts("Sent ICMP\n");
memset(&read_set, 0, sizeof read_set);
FD_SET(sock, &read_set);
//wait for a reply with a timeout
rc = select(sock + 1, &read_set, NULL, NULL, &timeout);
if (rc == 0) {
puts("Got no reply\n");
continue;
} else if (rc < 0) {
perror("Select");
break;
}
//we don't care about the sender address in this example..
slen = 0;
rc = recvfrom(sock, data, sizeof data, 0, NULL, &slen);
if (rc <= 0) {
perror("recvfrom");
break;
} else if (rc < sizeof rcv_hdr) {
printf("Error, got short ICMP packet, %d bytes\n", rc);
break;
}
memcpy(&rcv_hdr, data, sizeof rcv_hdr);
if (rcv_hdr.type == ICMP_ECHOREPLY) {
printf("ICMP Reply, id=0x%x, sequence = 0x%x\n",
icmp_hdr.un.echo.id, icmp_hdr.un.echo.sequence);
} else {
printf("Got ICMP packet with type 0x%x ?!?\n", rcv_hdr.type);
}
}
}
int main(int argc, char *argv[])
{
if (argc != 2) {
printf("usage: %s destination_ip\n", argv[0]);
return 1;
}
struct in_addr dst;
if (inet_aton(argv[1], &dst) == 0) {
perror("inet_aton");
printf("%s isn't a valid IP address\n", argv[1]);
return 1;
}
ping_it(&dst);
return 0;
}
请注意,如果发送的数据没有适当的ICMP标头空间,并且ICMP type
必须为8(ICMP_ECHO)并且ICMP代码必须为,则内核将拒绝并失败sendto()调用。 0
答案 1 :(得分:8)
是的,因为ping
命令可以执行ICMP。
要找出所涉及的系统调用,您可以strace
该命令(在根目录下)。
您还可以浏览该命令的源代码,例如: Debian's ping
还有liboping库来帮助你...