从路由器获取动态IP地址
关键词：DHCP W5500 WIZnet W5500EVB 动态获取IP
本节中W5500作为DHCP客户端，路由器作为DHCP服务器端。在DHCP请求的过程中，包括4个主要的阶段：发现阶段、提供阶段、选择阶段以及确认阶段。
下面来说一下整个DHCP请求流程。
首先W5500客户端发送DHCP DISCOVER消息（IP地址租用申请），这个消息通过广播方式发出，所有网络中的DHCP服务器都将接收到这个消息。随后，网络中的DHCP服务器会回应一个DHCPOFFER消息（IP地址租用提供），由于这个时候客户端还没有网络地址，所以DHCP OFFER也是通过广播的方式发送出去的。 后，向该服务器发送DHCP REQUEST消息。在DHCP REQUEST消息中将包含客户端然申请的IP地址。最后，DHCP服务器将回送DHCP ACK的响应消息来通知客户端可以使用该IP地址，该确认里面包含了分配的IP地址和该地址的一个稳定期限的租约（默认是8天），并同时更新DHCP数据库。
主循环代码如下: while(1)
{
DHCP_run();
}
uint8_t DHCP_run(void)
{
uint8_t type;
uint8_t ret;
if(dhcp_state == STATE_DHCP_STOP) return DHCP_STOPPED;
if(getSn_SR(SOCK_DHCP) != SOCK_UDP)
socket(SOCK_DHCP, Sn_MR_UDP, DHCP_CLIENT_PORT, 0x00);
ret = DHCP_RUNNING;
type = parseDHCPMSG();
switch ( dhcp_state )
{
case STATE_DHCP_READY :
DHCP_allocated_ip[0] = 0;
DHCP_allocated_ip[1] = 0;
DHCP_allocated_ip[2] = 0;
DHCP_allocated_ip[3] = 0;
send_DHCP_DISCOVER();
dhcp_time = 0;
dhcp_state = STATE_DHCP_DISCOVER;
break;
case STATE_DHCP_DISCOVER :
if (type == DHCP_OFFER)
{
#ifdef _DHCP_DEBUG_
printf("> Receive DHCP_OFFER\r\n");
#endif
DHCP_allocated_ip[0] = pDHCPMSG->yiaddr[0];
DHCP_allocated_ip[1] = pDHCPMSG->yiaddr[1];
DHCP_allocated_ip[2] = pDHCPMSG->yiaddr[2];
DHCP_allocated_ip[3] = pDHCPMSG->yiaddr[3];
send_DHCP_REQUEST();
dhcp_time = 0;
dhcp_state = STATE_DHCP_REQUEST;
}
else
ret = check_DHCP_timeout();
break;
case STATE_DHCP_REQUEST :
if (type == DHCP_ACK)
{
#ifdef _DHCP_DEBUG_
printf("> Receive DHCP_ACK\r\n");
#endif
if (check_DHCP_leasedIP())
{
printf("ip:%d.%d.%d.%d\r\n",DHCP_allocated_ip[0],DHCP_allocated_ip[1],DHCP_allocated_ip[2],DHCP_allocated_ip[3]);
printf("sn:%d.%d.%d.%d\r\n",DHCP_allocated_sn[0],DHCP_allocated_sn[1],DHCP_allocated_sn[2],DHCP_allocated_sn[3]);
printf("gw:%d.%d.%d.%d\r\n",DHCP_allocated_gw[0],DHCP_allocated_gw[1],DHCP_allocated_gw[2],DHCP_allocated_gw[3]);
dhcp_ip_assign();
reset_DHCP_timeout();
hcp_state = STATE_DHCP_LEASED;
}
else
{
reset_DHCP_timeout();
dhcp_ip_conflict();
dhcp_state = STATE_DHCP_READY;
}
}
else if (type == DHCP_NAK)
{
#ifdef _DHCP_DEBUG_
printf("> Receive DHCP_NACK\r\n");
#endif
reset_DHCP_timeout();
dhcp_state = STATE_DHCP_DISCOVER;
}
else
ret = check_DHCP_timeout();
break;
case STATE_DHCP_LEASED :
ret = DHCP_IP_LEASED;
if ((dhcp_lease_time != DEFAULT_LEASETIME) && ((dhcp_lease_time/2) < dhcp_time))
{
#ifdef _DHCP_DEBUG_
printf("> Maintains the IP address \r\n");
#endif
type = 0;
OLD_allocated_ip[0] = DHCP_allocated_ip[0];
OLD_allocated_ip[1] = DHCP_allocated_ip[1];
OLD_allocated_ip[2] = DHCP_allocated_ip[2];
OLD_allocated_ip[3] = DHCP_allocated_ip[3];
DHCP_XID++;
send_DHCP_REQUEST();
reset_DHCP_timeout();
dhcp_state = STATE_DHCP_REREQUEST;
}
break;
case STATE_DHCP_REREQUEST :
ret = DHCP_IP_LEASED;
if (type == DHCP_ACK)
{
dhcp_retry_count = 0;
if (OLD_allocated_ip[0] != DHCP_allocated_ip[0] ||
OLD_allocated_ip[1] != DHCP_allocated_ip[1] ||
OLD_allocated_ip[2] != DHCP_allocated_ip[2] ||
OLD_allocated_ip[3] != DHCP_allocated_ip[3])
{
ret = DHCP_IP_CHANGED;
dhcp_ip_update();
#ifdef _DHCP_DEBUG_
printf(">IP changed.\r\n");
#endif
}
#ifdef _DHCP_DEBUG_
else printf(">IP is continued.\r\n");
#endif
reset_DHCP_timeout();
dhcp_state = STATE_DHCP_LEASED;
}
else if (type == DHCP_NAK)
{
#ifdef _DHCP_DEBUG_
printf("> Receive DHCP_NACK, Failed to maintain ip\r\n");
#endif
reset_DHCP_timeout();
dhcp_state = STATE_DHCP_DISCOVER;
}
else ret = check_DHCP_timeout();
break;
default :
break;
}
return ret;
}
DHCP的测试步骤如下
- DHCP例程将动态获取的IP信息配置给W5500，所以在w5500_conf.c文件中设置ip_from为IP_FROM_DHCP。
- 对代码进行编译，之后将程序烧录到野火开发板。
- 连接好网线，USB串口线。打开串口调试工具，复位野火开发板，从输出结果可以得到图1设置信息。
- 在Windows下的具体操作是，开始→运行→（键入）cmd，输入 ping 192.168.1.109→回车，看到回复信息如图2所示。可以成功ping到通过DHCP动态获取分配给W5500的IP地址，可以看到整个过程是如此的简单。
图1：DHCP动态获取信息
图2：ping DHCP 获取IP地址
例程下载：【DHCP】
编译环境：keil V5.11
硬件要求：W5500EVB