数据发送正常，但tcpdump捕获不到数据包？？？

[albon_arith]

首先，程序算UNIX网络编程里的，服务器tcpserv09.c和客户端tcpcli09.c

root@ubuntu:~# netstat -a
激活Internet连接 (服务器和已建立连接的)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 *:9877 *:* LISTEN

用的是端口9877

root@ubuntu:~/下载/unpv12e/tcpcliserv# ./tcpcli09 211.69.205.233
3 5
8

客户端发送两个数字，收到他们的和，211.69.205.233是本机IP地址。

tcpdump port 9877

服务器端和客户端程序都运行正常，但tcpdump却捕获不到9877端口的包，是哪里的错误ni？该怎么修改？

[albon_arith]

tcpserv09.c

#include        "unp.h"

int
main(int argc, char **argv)
{
        int                                        listenfd, connfd;
        pid_t                                childpid;
        socklen_t                        clilen;
        struct sockaddr_in        cliaddr, servaddr;
        void                                sig_chld(int);

        listenfd = Socket(AF_INET, SOCK_STREAM, 0);

        bzero(&servaddr, sizeof(servaddr));
        servaddr.sin_family      = AF_INET;
        servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
        servaddr.sin_port        = htons(SERV_PORT);

        Bind(listenfd, (SA *) &servaddr, sizeof(servaddr));

        Listen(listenfd, LISTENQ);

        Signal(SIGCHLD, sig_chld);

        for ( ; ; ) {
                clilen = sizeof(cliaddr);
                if ( (connfd = accept(listenfd, (SA *) &cliaddr, &clilen)) < 0) {
                        if (errno == EINTR)
                                continue;                /* back to for() */
                        else
                                err_sys("accept error");
                }

                if ( (childpid = Fork()) == 0) {        /* child process */
                        Close(listenfd);        /* close listening socket */
                        str_echo(connfd);        /* process the request */
                        exit(0);
                }
                Close(connfd);                        /* parent closes connected socket */
        }
}

tcpcli09.c

#include        "unp.h"

int
main(int argc, char **argv)
{
        int                                        sockfd;
        struct sockaddr_in        servaddr;

        if (argc != 2)
                err_quit("usage: tcpcli <IPaddress>");

        sockfd = Socket(AF_INET, SOCK_STREAM, 0);

        bzero(&servaddr, sizeof(servaddr));
        servaddr.sin_family = AF_INET;
        servaddr.sin_port = htons(SERV_PORT);
        Inet_pton(AF_INET, argv[1], &servaddr.sin_addr);

        Connect(sockfd, (SA *) &servaddr, sizeof(servaddr));

        str_cli(stdin, sockfd);                /* do it all */

        exit(0);
}

[albon_arith]

难道tcpdump不捕获本机到本机的包？

[root_jli]

要抓取本机的需监听lo0
tcpdump -i lo port 9877