未找到rt_msghdr结构定义，如何通过UNIX网络API获取路由表信息？

Hey there, let's clear up this confusion and get you on track to fetching routing table info on your Kali system.

The Root Cause #

The rt_msghdr struct you're looking for is a BSD-specific routing message structure—Linux doesn't include it in its header files. Instead, Linux uses the Netlink API (specifically the rtnetlink subsystem) for kernel-user space communication related to routing, which relies on a different set of structures and headers.

Step-by-Step Solution #

1. Switch to the Correct Header File
   Replace <net/route.h> with <linux/rtnetlink.h>—this is the standard header for Linux routing operations via Netlink. It defines all the necessary structures like struct rtmsg (the Linux equivalent of BSD's rt_msghdr) and struct nlmsghdr (the Netlink message wrapper).

2. Use Linux's Routing API Structures
   Instead of rt_msghdr, you'll work with two key structures:

   • struct nlmsghdr: The top-level Netlink message header that wraps all routing-related payloads.
   • struct rtmsg: The core structure for specifying routing table query parameters (like address family, target route table, etc.).

3. Example Code Snippet
   Here's a minimal example to set up a Netlink socket and send a request to fetch the IPv4 main routing table:

   #include <stdio.h>
   #include <stdlib.h>
   #include <string.h>
   #include <sys/socket.h>
   #include <linux/rtnetlink.h>
   #include <unistd.h>
   
   int main() {
       int sockfd;
       struct sockaddr_nl sa;
       struct nlmsghdr *nlh;
       struct rtmsg *rtm;
       ssize_t recv_len;
       char buf[8192];
   
       // Create Netlink routing socket
       sockfd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
       if (sockfd < 0) {
           perror("Failed to create socket");
           exit(EXIT_FAILURE);
       }
   
       // Configure Netlink socket address
       memset(&sa, 0, sizeof(sa));
       sa.nl_family = AF_NETLINK;
       sa.nl_pid = getpid();
       sa.nl_groups = RTMGRP_IPV4_ROUTE;
   
       // Allocate and initialize Netlink message
       nlh = (struct nlmsghdr *)malloc(NLMSG_SPACE(sizeof(struct rtmsg)));
       if (!nlh) {
           perror("Failed to allocate memory");
           close(sockfd);
           exit(EXIT_FAILURE);
       }
       memset(nlh, 0, NLMSG_SPACE(sizeof(struct rtmsg)));
       nlh->nlmsg_len = NLMSG_SPACE(sizeof(struct rtmsg));
       nlh->nlmsg_type = RTM_GETROUTE;
       nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP; // Request full table dump
       nlh->nlmsg_seq = 1;
       nlh->nlmsg_pid = getpid();
   
       // Populate routing query parameters
       rtm = NLMSG_DATA(nlh);
       rtm->rtm_family = AF_INET; // Target IPv4 routing table
       rtm->rtm_table = RT_TABLE_MAIN; // Query the main route table
       rtm->rtm_scope = RT_SCOPE_UNIVERSE;
   
       // Send the request to the kernel
       if (sendto(sockfd, nlh, nlh->nlmsg_len, 0, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
           perror("Failed to send request");
           free(nlh);
           close(sockfd);
           exit(EXIT_FAILURE);
       }
   
       // Receive and process the response (simplified)
       recv_len = recv(sockfd, buf, sizeof(buf), 0);
       if (recv_len < 0) {
           perror("Failed to receive response");
       } else {
           printf("Received routing table data (length: %zd bytes)\n", recv_len);
           // Parse the response using the NLMSG_NEXT() macro to iterate over messages
       }
   
       // Cleanup
       free(nlh);
       close(sockfd);
       return 0;
   }
   

4. Deepen Your Knowledge with Man Pages
   For detailed documentation on all rtnetlink structures, message types, and parsing logic, run:

   man 7 rtnetlink
   

   This covers everything you need to handle complex routing operations and parse the kernel's response fully.

内容的提问来源于stack exchange，提问作者P.Carlino