第二章 W55MH32 DHCP示例
目录
1 DHCP协议简介
2 DHCP协议特点
3 DHCP工作原理
4 DHCP协议报文
5 DHCP应用场景
6 实现过程
8 运行结果
7 总结
本篇文章我们将详细讲解DHCP协议的基本信息、优势特点、工作原理、应用场景,并通过实战例程,为大家讲解如何使用W55MH32动态获取IP信息,帮助读者更好地了解并运用这一协议。
有关W55MH32的初始化过程,请参考相关章节,这里将不再详述。
1 DHCP协议简介
DHCP(Dynamic Host Configuration Protocol)即动态主机配置协议,是一个应用层协议。它主要用于在 IP 网络中为客户端自动分配 IP 地址及其他相关网络配置参数,如子网掩码、默认网关、DNS 服务器地址等。这种动态分配的方式大大简化了网络管理员的工作,并且能够更有效地利用有限的 IP 地址资源。
2 DHCP协议特点
- 便捷配置与管控:DHCP可自动分配IP地址、子网掩码、网关、DNS等网络参数,设备入网即自动获取,用户无需手动操作。管理员能通过服务器集中管理IP分配,网络架构调整时,修改服务器设置,客户端自动适配;静态IP则要逐台手动输入、调整,流程繁琐还易出错。
- 灵活资源利用:DHCP动态分配IP,设备离线后地址回池再利用,契合公共场所临时大量接入需求,提升地址利用率;还能按需灵活调配,为关键设备保留静态IP,其余动态分配。静态IP固定占用,闲置浪费资源,灵活性差。
- 高效维护与排障:DHCP自动分配,规避手动配置错误与IP地址冲突,服务器详细记录分配情况。网络故障时,管理员依服务器日志锁定故障设备排查;静态IP手动配置易冲突,故障排查缺少有效记录,难度大、耗时久。
- 适配移动与拓展:移动设备横跨网络时,DHCP让其自动获取IP配置,无需手动切换;网络规模扩大、新增设备时,DHCP自动分配地址,助力快速扩容。静态IP需提前规划,易现地址不足、分配不合理问题,还增加设备移动操作难度。
3 DHCP工作原理
DHCP工作原理如图所示:
从图示中我们可以直观明了地看出DHCP地工作原理,一般为四个阶段:
- 发现阶段:客户端接入网络时以广播形式发送DHCP Discover报文(目的IP是255.255.255.255,源IP是0.0.0.0)寻找DHCP服务器,报文中含客户端MAC地址。若服务器和客户端不在同一子网,会通过中继代理(如路由器)转发。
- 提供阶段:DHCP服务器收到Discover报文后,从IP地址池选一个未分配的IP地址,将其和子网掩码、默认网关、DNS服务器地址等信息封装进DHCP Offer报文,以广播或单播方式发给客户端,可能会有多个Offer报文。
- 请求阶段:客户端收到多个Offer后选择一个,以广播形式发送DHCP Request报文请求分配该IP地址等配置信息,且发送ARP请求检查IP地址唯一性。
- 确认阶段:服务器收到Request报文后,检查IP地址是否可用。若可用,将以广播或单播的形式发送DHCP Ack报文,客户端收到后完成网络配置正常上网。若不可用,发送DHCP Nak报文,客户端收到后重新发起Discover流程。
4 DHCP协议报文
DHCP的报文格式如下:
0~7 bit | 8~15 bit | 16~23 bit | 24~31 bit |
op(1) | htype(1) | hlen(1) | hops(1) |
Xid(4) | |||
secs(2) | flags(2) | ||
ciaddr(4) | |||
yiaddr(4) | |||
siaddr(4) | |||
giaddr(4) | |||
chaddr(16) | |||
sname(64) | |||
file(128) | |||
options(variable) |
DHCP报文各字段的说明如下表所示:
字段 | 长度 | 含义 |
op(op code) | 1字节 | 表示报文的类型,取值为1或2,含义如下: 1:客户端请求报文。 2:服务器响应报文。 |
htype(hardware type) | 1字节 | 表示硬件类型。不同的硬件类型取值不同,常见值为1,表示以太网(10Mb)。 |
hlen(hardware length) | 1字节 | 表示硬件地址长度,以太网的值为6。 |
hops | 1字节 | 表示DHCP报文经过的DHCP中继数目。客户端或服务器初始设为0,每经过一个中继则加1,用于限制DHCP报文经过的中继数量,且服务器与客户端间中继数目不能超16个(Hops值不能大于16),否则报文将被丢弃。 |
xid | 4字节 | 表示DHCP客户端选取的随机数,使DHCP服务器的回复与DHCP客户端的报文相关联。 |
secs(seconds) | 2字节 | 表示客户端从开始获取地址或地址续租更新后所用的时间,单位是秒。 |
flags | 2字节 | 表示标志字段。只有标志字段的最高位才有意义,其余的15位均被置为0。最高位被解释为单播或者广播响应标志位,内容如下所示: 0:客户端请求服务器以单播形式发送响应报文。 1:客户端请求服务器以广播形式发送响应报文。 |
ciaddr(client ip address) | 4字节 | 表示客户端的IP地址。可以是服务器分配给客户端的IP地址或者客户端已有的IP地址。客户端在初始化状态时没有IP地址,此字段为0.0.0.0。 IP地址0.0.0.0仅在采用DHCP方式的系统启动时允许本主机利用它进行临时的通信,不是有效目的地址。 |
yiaddr(your client ip address) | 4字节 | 表示服务器分配给客户端的IP地址。当服务器进行DHCP响应时,将分配给客户端的IP地址填入此字段。 |
siaddr(server ip address) | 4字节 | DHCP客户端获得启动配置信息的服务器的IP地址。 |
giaddr(gateway ip address) | 4字节 | 表示首个DHCP中继的IP地址。客户端发DHCP请求,若服务器与客户端不在同一网段,首个中继转发请求报文给服务器时填入自身IP地址,服务器据此判断客户端网段地址,选地址池分配对应IP地址,再按此地址回发响应报文给该中继,由中继转发给客户端。若存在多个中继,此字段作为客户端网段标记,填好首个中继IP地址后不再变更,每经过一个中继,hops字段数值加1。 |
chaddr(client hardware address) | 16字节 | 表示客户端的MAC地址,此字段与前面的“hardware type”和“hardware length”保持一致。当客户端发出DHCP请求时,将自己的硬件地址填入此字段。对于以太网,当“hardware type”和“hardware length”分别为“1”和“6”时,此字段必须填入6字节的以太网MAC地址。 |
sname(server host name) | 64字节 | 表示客户端获取配置信息的服务器名字。此字段由DHCP服务器填写,是可选的。如果填写,必须是一个以0结尾的字符串。 |
file(file name) | 128字节 | 表示客户端需获取的启动配置文件名。由DHCP服务器填写,随DHCP地址分配下发至客户端。该字段可选,若填写则须是以0结尾的字符串。 |
options | 可变 | 表示DHCP的选项字段,最多1200字节,包含DHCP报文类型、服务器分配给终端的配置信息(如网关IP地址、DNS服务器IP地址、客户端IP地址有效租期等)。详情参见IETF官网“DHCP Options”部分的描述。 |
Discover报文实例:客户端通过UDP广播的方式发送DHCP发现报文,报文中包含了客户端MAC地址、主机名和请求的IP地址等信息
|报文解析|
Message type: Boot Request (1) (op code为1,客户端请求报文)
Hardware type: Ethernet (0x01)
Hardware address length: 6
Hops: 0
Transaction ID: 0xbf600589
Seconds elapsed: 0
Bootp flags: 0x0000 (Unicast)
Client IP address: 0.0.0.0
Your (client) IP address: 0.0.0.0
Next server IP address: 0.0.0.0
Relay agent IP address: 0.0.0.0
Client MAC address: HP_b1:37:11 (64:4e:d7:b1:37:11)
Client hardware address padding: 00000000000000000000
Server host name not given
Boot file name not given
Magic cookie: DHCP
Option: (53) DHCP Message Type (Discover)
Option: (61) Client identifier
Option: (50) Requested IP Address (192.168.1.115)
Option: (12) Host Name
Option: (60) Vendor class identifier
Option: (55) Parameter Request List
Option: (255) End
Padding: 0000000000000000
|报文原文|
01 01 06 00 bf 60
05 89 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 64 4e d7 b1 37 11 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 63 82 53 63 35 01 01 3d 07 01 64 4e d7 b1 37 11 32 04 c0 a8 01 73 0c 05 46 41 45 5f 33 3c 08 4d 53 46 54 20 35 2e 30 37 0e 01 03 06 0f 1f 21 2b 2c 2e 2f 77 79 f9 fc ff 00 00 00 00 00 00 00 00
Offer报文实例:DHCP服务器收到Discover报文后,从IP地址池选一个未分配的IP地址,将其和子网掩码、默认网关等信息封装进Offer报文以广播或单播(这里为广播的方式)方式发给客户端
|报文解析|
Message type: Boot Reply (2) (op code为2,服务器响应报文)
Hardware type: Ethernet (0x01)
Hardware address length: 6
Hops: 0
Transaction ID: 0xbf600589
Seconds elapsed: 0
Bootp flags: 0x0000 (Unicast)
Client IP address: 0.0.0.0
Your (client) IP address: 192.168.1.115
Next server IP address: 0.0.0.0
Relay agent IP address: 0.0.0.0
Client MAC address: HP_b1:37:11 (64:4e:d7:b1:37:11)
Client hardware address padding: 00000000000000000000
Server host name not given
Boot file name not given
Magic cookie: DHCP
Option: (53) DHCP Message Type (Offer)
Option: (54) DHCP Server Identifier (192.168.1.1)
Option: (51) IP Address Lease Time
Option: (6) Domain Name Server
Option: (1) Subnet Mask (255.255.255.0)
Option: (3) Router
Option: (255) End
|报文原文|
02 01 06 00 bf 60
05 89 00 00 00 00 00 00 00 00 c0 a8 01 73 00 00 00 00 00 00 00 00 64 4e d7 b1 37 11 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 63 82 53 63 35 01 02 36 04 c0 a8 01 01 33 04 00 00 1c 20 06 08 ca 60 86 21 ca 60 80 56 01 04 ff ff ff 00 03 04 c0 a8 01 01 ff
其他报文信息这里就不一一展示了,感兴趣的朋友可以自行抓取查看。
5 DHCP应用场景
DHCP的应用场景通常集中在需要动态分配IP地址的局域网环境中。例如,在大型的办公环境或者学校中,由于有大量的网络设备需要连接到网络,手动为每个设备分配和管理IP地址会非常繁琐且容易出错。使用DHCP可以集中管理IP地址的分配,提高网络管理员的工作效率,减少错误的发生,且可以适应网络变化。
6 实现过程
接下来,我们一起来看看如何在W55MH32上实现DHCP动态获取网络地址信息。
注意:使用DHCP动态获取IP时,必需将网络结构体配置中dhcp的值改为NETINFO_DHCP,这样才能运行DHCP模式。
步骤一:注册DHCP定时器中断到1s定时器中:
/**
* @brief 1ms timer IRQ Handler
* @param none
* @return none
*/
void TIM3_IRQHandler(void)
{static uint32_t tim3_1ms_count = 0;if (TIM_GetITStatus(TIM3, TIM_IT_Update) != RESET){tim3_1ms_count++;if (tim3_1ms_count >= 1000){DHCP_time_handler();tim3_1ms_count = 0;}TIM_ClearITPendingBit(TIM3, TIM_IT_Update);}
}
注册DHCP定时器中断主要为了DHCP超时处理。
在dhcp.h文件中,定义了DHCP超时时间、重试次数、端口号和主机名等内容:
#ifndef _DHCP_H_
#define _DHCP_H_#ifdef __cplusplus
extern "C" {
#endif/*
* @brief
* @details If you want to display debug & processing message, Define _DHCP_DEBUG_
* @note If defined, it depends on <stdio.h>
*/
//#define _DHCP_DEBUG_/* Retry to processing DHCP */
#define MAX_DHCP_RETRY 2 ///< Maximum retry count
#define DHCP_WAIT_TIME 10 ///< Wait Time 10s/* UDP port numbers for DHCP */
#define DHCP_SERVER_PORT 67 ///< DHCP server port number
#define DHCP_CLIENT_PORT 68 ///< DHCP client port number#define MAGIC_COOKIE 0x63825363 ///< You should not modify it number.#define DCHP_HOST_NAME "WIZnet\0"
步骤二:启用DHCP动态获取:
首先需要将默认网络地址信息结构体中的模式改为DHCP模式
/* network information */
wiz_NetInfo default_net_info = {.mac = {0x00, 0x08, 0xdc, 0x12, 0x22, 0x12},.ip = {192, 168, 1, 30},.gw = {192, 168, 1, 1},.sn = {255, 255, 255, 0},.dns = {8, 8, 8, 8},.dhcp = NETINFO_DHCP
};
步骤三:DHCP获取网络地址信息
首先是在初始化完硬件和TOE之后调用network_init进行网络地址信息配置
network_init(ethernet_buf, &default_net_info);
这个函数需要将DHCP处理用到的缓存数组以及默认网络地址信息传入,函数具体内容如下:
/**
* @brief set network information
*
* First determine whether to use DHCP. If DHCP is used, first obtain the Internet Protocol Address through DHCP.
* When DHCP fails, use static IP to configure network information. If static IP is used, configure network information directly
*
* @param sn: socketid
* @param ethernet_buff:
* @param net_info: network information struct
* @return none
*/
void network_init(uint8_t *ethernet_buff, wiz_NetInfo *conf_info)
{int ret;wizchip_setnetinfo(conf_info); // Configuring Network Informationif (conf_info->dhcp == NETINFO_DHCP){ret = wiz_dhcp_process(0, ethernet_buff);if (ret == 0){conf_info->dhcp = NETINFO_STATIC;wizchip_setnetinfo(conf_info);}}print_network_information();
}
在这个函数中,会先设置一遍网络地址到W55MH32中,然后判断模式是否为DHCP模式,如果为DHCP模式,则使用wiz_dhcp_process函数来执行DHCP进程,在通过DHCP方式成功获取到网络地址后更新到W55MH32中,最后将网络地址信息打印出来。wiz_dhcp_process函数内容如下:
/**
* @brief DHCP process
* @param sn :socket number
* @param buffer :socket buffer
*/
static uint8_t wiz_dhcp_process(uint8_t sn, uint8_t *buffer)
{wiz_NetInfo conf_info;uint8_t dhcp_run_flag = 1;uint8_t dhcp_ok_flag = 0;/* Registration DHCP_time_handler to 1 second timer */DHCP_init(sn, buffer);printf("DHCP running\r\n");while (1){switch (DHCP_run()) // Do the DHCP client{case DHCP_IP_LEASED: // DHCP Acquiring network information successfullyif (dhcp_ok_flag == 0){dhcp_ok_flag = 1;dhcp_run_flag = 0;}break;case DHCP_FAILED:dhcp_run_flag = 0;break;}if (dhcp_run_flag == 0){printf("DHCP %s!\r\n", dhcp_ok_flag ? "success" : "fail");DHCP_stop();if (dhcp_ok_flag){getIPfromDHCP(conf_info.ip);getGWfromDHCP(conf_info.gw);getSNfromDHCP(conf_info.sn);getDNSfromDHCP(conf_info.dns);conf_info.dhcp = NETINFO_DHCP;getSHAR(conf_info.mac);wizchip_setnetinfo(&conf_info); // Update network information to network information obtained by DHCPreturn 1;}return 0;}}
}
在该函数体中,首先会调用DHCP_init 函数进行初始化DHCP配置:
void DHCP_init(uint8_t s, uint8_t * buf)
{uint8_t zeroip[4] = {0, 0, 0, 0};getSHAR(DHCP_CHADDR);if ((DHCP_CHADDR[0] | DHCP_CHADDR[1] | DHCP_CHADDR[2] | DHCP_CHADDR[3] | DHCP_CHADDR[4] | DHCP_CHADDR[5]) == 0x00){// Assigning temporary mac address, you should set SHAR before calling this function.DHCP_CHADDR[0] = 0x00;DHCP_CHADDR[1] = 0x08;DHCP_CHADDR[2] = 0xdc;DHCP_CHADDR[3] = 0x00;DHCP_CHADDR[4] = 0x00;DHCP_CHADDR[5] = 0x00;setSHAR(DHCP_CHADDR);}DHCP_SOCKET = s; // SOCK_DHCPpDHCPMSG = (RIP_MSG*)buf;DHCP_XID = 0x12345678;{DHCP_XID += DHCP_CHADDR[3];DHCP_XID += DHCP_CHADDR[4];DHCP_XID += DHCP_CHADDR[5];DHCP_XID += (DHCP_CHADDR[3] ^ DHCP_CHADDR[4] ^ DHCP_CHADDR[5]);}// WIZchip Netinfo ClearsetSIPR(zeroip);setGAR(zeroip);reset_DHCP_timeout();dhcp_state = STATE_DHCP_INIT;
}
然后是在DHCP主循环中运行DHCP_run函数,它的主要作用是进行DHCP组包,发送发现、请求等报文,对服务器的提供、响应等内容进行解析以及超时处理,这里只需要根据DHCP_run函数的返回值进行相应处理即可。DHCP_run函数内容如下:
uint8_t DHCP_run(void)
{uint8_t type;uint8_t ret;if(dhcp_state == STATE_DHCP_STOP) return DHCP_STOPPED;if(getSn_SR(DHCP_SOCKET) != SOCK_UDP)socket(DHCP_SOCKET, Sn_MR_UDP, DHCP_CLIENT_PORT, 0x00);ret = DHCP_RUNNING;type = parseDHCPMSG();switch ( dhcp_state ) {case STATE_DHCP_INIT :DHCP_allocated_ip[0] = 0;DHCP_allocated_ip[1] = 0;DHCP_allocated_ip[2] = 0;DHCP_allocated_ip[3] = 0;send_DHCP_DISCOVER();dhcp_state = STATE_DHCP_DISCOVER;break;case STATE_DHCP_DISCOVER :if (type == DHCP_OFFER){
#ifdef _DHCP_DEBUG_printf("> Receive DHCP_OFFER\r\n");
#endifDHCP_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_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");
#endifif (check_DHCP_leasedIP()) {// Network info assignment from DHCPdhcp_ip_assign();reset_DHCP_timeout();dhcp_state = STATE_DHCP_LEASED;} else {// IP address conflict occurredreset_DHCP_timeout();dhcp_ip_conflict();dhcp_state = STATE_DHCP_INIT;}} else if (type == DHCP_NAK) {#ifdef _DHCP_DEBUG_printf("> Receive DHCP_NACK\r\n");
#endifreset_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 != INFINITE_LEASETIME) && ((dhcp_lease_time/2) < dhcp_tick_1s)) {#ifdef _DHCP_DEBUG_printf("> Maintains the IP address \r\n");
#endiftype = 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");
#endifreset_DHCP_timeout();dhcp_state = STATE_DHCP_DISCOVER;} else ret = check_DHCP_timeout();break;default :break;}return ret;
}
7 运行结果
烧录例程运行后,首先打印了PHY链路检测的结果以及DHCP日志信息,然后打印了网络地址信息,这里可以看到配置方式为DHCP,IP地址为192.168.1.117,最后是PING提示消息。
接着在PC端打开CMD,PING W55MH32的IP地址,可以正常PING通。
8 总结
本文介绍 DHCP 协议,包括其在 IP 网络自动分配参数的功能、便捷配置等特点、工作原理、报文格式和应用场景。通过 W55MH32 实战例程展示动态获取网络地址信息过程,含注册定时器中断、启用模式和获取信息等步骤,烧录后可完成检测与信息打印,PC 端能 PING 通设备。
下一篇文章将讲解如何在 W55MH32 芯片上实现 TCP 客户端模式,解析 TCP 客户端连接服务器进行回环测试的核心原理及应用,同时通过实战例程讲解具体实现步骤与要点,敬请期待