关于udp 端口不可达的问题

Question

背景：服务器和客户端需要使用同一个端口，进行udp数据包的互传，发送过程都没有问题，抓包软件抓到的包也正常，但是为什么在接收的时候显示了icmp端口不可达问题。代码在下面，DEV_BIND_S过程中向服务器发送了一个udp单播，DEV_DATA_RW_S中接收服务器udp单播失败了。

case DEV_BIND_S:
            /* Bind socket (optional) */
            addr_local.sin_family = AF_INET;
            addr_local.sin_port = FNET_HTONS(50002);
            addr_local.sin_addr.s_addr = FNET_HTONL(INADDR_ANY);
            //addr_local.sin_scope_id = 0;
            if (fnet_socket_bind( update_handle->socket_id, (struct fnet_sockaddr *)&addr_local, sizeof(addr_local)) == FNET_ERR)
            {
                fnet_printf("bind update_confirm socket fail \r\n");
                closesocket(update_handle->socket_id);
                update_handle->socket_state = DEV_INIT_S;
            } else {
                add_remote.sa_family = AF_INET;
                add_remote.sa_port = addr_local.sin_port;
                update_handle->fapp_client_ack.code=0;
                memcpy(add_remote.sa_data, update_handle->update_info.serverIP, VERSION_INFO_MAX_LEN);
                if(sendto(update_handle->socket_id, &update_handle->fapp_client_ack,
                   sizeof(update_handle->fapp_client_ack), 0, (struct fnet_sockaddr *)&add_remote, sizeof(add_remote)) < 0) {
                   fnet_printf("admin socket sendto error \r\n");
                   closesocket(update_handle->socket_id);
                   update_handle->socket_state = DEV_INIT_S;
                   return;
                }
                update_handle->socket_state = DEV_DATA_RW_S;
            }
            break;
        case DEV_DATA_RW_S:
            recv_size = recvfrom(update_handle->socket_id, recv_buff, sizeof(recv_buff), 0, (struct fnet_sockaddr *)&add_remote, &fromlen);
            if(recv_size==0){
            update_handle->socket_state = DEV_DATA_RW_S;
            }
            else if (recv_size != sizeof(fapp_update_confirm_t)) {
                fnet_printf("update confirm socket recv error\r\n");
                //update_confirm_socket_close();
                closesocket(update_handle->socket_id);
                update_handle->socket_state = DEV_INIT_S;
            } 
            else {
                fapp_handle_update_cmd(recv_buff);
            }
            break;

Answer 1

udp通讯，发送与接收不能用同一个端口。