第2章 以太网与二层通信

struct net_bridge {
    struct list_head port_list;    // 端口列表
    struct hlist_head hash[BR_HASH_SIZE]; // FDB哈希表
    struct net_device *dev;        // Bridge设备
    // ... 更多字段
};

struct net_bridge_port {
    struct net_bridge *br;         // 所属Bridge
    struct net_device *dev;        // 端口设备
    struct hlist_head hash[BR_HASH_SIZE]; // 端口FDB
    // ... 更多字段
};

struct neigh_table arp_tbl = {
    .family = AF_INET,
    .key_len = 4,           // IP地址长度
    .hash = arp_hash,
    .constructor = arp_constructor,
    .pconstructor = arp_constructor,
    .pdestructor = arp_destructor,
    .proxy_redo = parp_redo,
    .id = "arp_cache",
    .parms = {
        .tbl = &arp_tbl,
        .reachable_time = 30 * HZ,
        .data = {
            [NEIGH_VAR_MCAST_PROBE] = 3,
            [NEIGH_VAR_UCAST_PROBE] = 3,
            [NEIGH_VAR_APP_PROBES] = 0,
            [NEIGH_VAR_RETRANS_TIME] = 1 * HZ,
            [NEIGH_VAR_BASE_REACHABLE_TIME] = 30 * HZ,
            [NEIGH_VAR_DELAY_PROBE_TIME] = 5 * HZ,
            [NEIGH_VAR_GC_STALETIME] = 60 * HZ,
            [NEIGH_VAR_QUEUE_LEN] = 3,
            [NEIGH_VAR_QUEUE_LEN_BYTES] = 64 * 1024,
            [NEIGH_VAR_PROXY_QLEN] = 64,
            [NEIGH_VAR_ANYCAST_DELAY] = 1 * HZ,
            [NEIGH_VAR_PROXY_DELAY] = (8 * HZ) / 10,
            [NEIGH_VAR_LOCKTIME] = 1 * HZ,
        },
    },
    .gc_interval = 30 * HZ,
    .gc_thresh1 = 128,
    .gc_thresh2 = 512,
    .gc_thresh3 = 1024,
};

// arp_learning.c
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <net/if.h>

struct arp_hdr {
    unsigned short ar_hrd;    // 硬件类型
    unsigned short ar_pro;    // 协议类型
    unsigned char  ar_hln;    // 硬件地址长度
    unsigned char  ar_pln;    // 协议地址长度
    unsigned short ar_op;     // 操作码
    unsigned char  ar_sha[6]; // 发送方硬件地址
    unsigned char  ar_sip[4]; // 发送方IP地址
    unsigned char  ar_tha[6]; // 目标硬件地址
    unsigned char  ar_tip[4]; // 目标IP地址
};

int main() {
    int sock = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ARP));
    if (sock < 0) {
        perror("socket");
        return 1;
    }
    
    char buffer[1024];
    while (1) {
        int len = recv(sock, buffer, sizeof(buffer), 0);
        if (len < 0) {
            perror("recv");
            continue;
        }
        
        struct arp_hdr *arp = (struct arp_hdr*)(buffer + 14);
        
        if (ntohs(arp->ar_op) == 1) { // ARP请求
            printf("ARP Request: Who has %d.%d.%d.%d? Tell %d.%d.%d.%d\n",
                   arp->ar_tip[0], arp->ar_tip[1], arp->ar_tip[2], arp->ar_tip[3],
                   arp->ar_sip[0], arp->ar_sip[1], arp->ar_sip[2], arp->ar_sip[3]);
        } else if (ntohs(arp->ar_op) == 2) { // ARP应答
            printf("ARP Reply: %d.%d.%d.%d is at %02x:%02x:%02x:%02x:%02x:%02x\n",
                   arp->ar_sip[0], arp->ar_sip[1], arp->ar_sip[2], arp->ar_sip[3],
                   arp->ar_sha[0], arp->ar_sha[1], arp->ar_sha[2],
                   arp->ar_sha[3], arp->ar_sha[4], arp->ar_sha[5]);
        }
    }
    
    close(sock);
    return 0;
}