【无OS】基于STM32移植LWIP 1.4.1之DNS

更新时间:2023-04-04 06:33:19 阅读：评论：0

文章目录

1.前言2.LwI殿的组词P如何实现DNS功能3.dns_init主要流程4.如何获取DNS Server地址5. DNS域名解析流程6. DNS分析的设备Log7.资料下载地址

1.前言

DNS(Domain Name System)域名系统，主要实现的功能是将域名转换成ip地址的一个服务。它是由一个分层的DNS服务器实现的分布式数据库。同时，他也是一个使得主机能够查询分布式数据库的应用层协议。DNS服务器通常是一个运行BIND(Berkeley Internet Name Domain)软件的UNIX机器。DNS协议运行在UDP之上，使用53号端口。

由于有之前实现DHCP功能的基础《【无OS】基于STM32移植LWIP 1.4.1之DHCP》，所以DNS的移浙江有哪些二本大学植很简单，下面将主要介绍LwIP DNS的流程分析。

2.LwIP如何实现DNS功能

LwIP基本上已经实现了DNS功能，我只需要打开相关的宏就可以，操作如下：

在lwipopts.h定义LWIP_DNS，打开DNS功能;在netconf.c的LwIP_Init函数中调用dns_init，来初始化DNS客户端；DHCP动态获取IP地址后，再调用DNS API dns_gethostbyname进行DNS域名解析。（参考代码如下：LwIP_DNS_Test）

--- a/stm我可能不会爱你电视剧32f429_lwip_pro_list/2.stm32f429_lwip_basic_dhcp/Ur/LAN8742A/netconf.c+++ b/stm32f429_lwip_pro_list/2.stm32f429_lwip_basic_dhcp/Ur/LAN8742A/netconf.c@@ -31,6 +31,7 @@ #include "lwip/tcp.h" #include "lwip/tcp_impl.h" #include "lwip/udp.h"+#include "lwip/dns六级考试题型.h" #include "netif/etharp.h" #include "lwip/dhcp.h" #include "ethernetif.h"@@ -137,6 +138,11 @@ void LwIP_Init(void)      /* Set the link callback function, this function is called on change of link status*/   netif_t_link_callback(&gnetif, ETH_link_callback);++#if LWIP_DNS+  dns_init();+#endif /* LWIP_DNS */+   } +#ifdef LWIP_DNS+void LwIP_DNS_Callback_handler(const char *name, struct ip_addr *ipaddr, void *arg)+{ +uint8_t ip[4];++ip[0] = ipaddr->addr>>24; +ip[1] = ipaddr->addr>>16;+ip[2] = ipaddr->addr>>8; +ip[3] = ipaddr->addr; ++printf("[%s]域名解析的IP:%d.%d.%d.%d\n",name,ip[3], ip[2], ip[1], ip[0]); +}+void LwIP_DNS_Test(void)+{ +struct ip_addr DNS_IP;+char hostname[] = "www.qq.com";++printf("\r\n开始DNS解析：%s\r\n", hostname);+dns_gethostbyname(hostname, &DNS_IP, LwIP_DNS_Callback_handler, NULL);+}++#endif+ #ifdef USE_DHCP@@ -265,6 +294,10 @@ void LwIP_DHCP_Process_Handle() sprintf((char*)mactxt, " %02x-%02x-%02x-%02x-%02x-%02x", gnetif.hwaddr[0], gnetif.hwaddr[1], gnetif.hwaddr[2], gnetif.hwaddr[3], gnetif.hwaddr[4], gnetif.hwaddr[5]); printf("MAC addr: %s\r\n", mactxt); +#ifdef LWIP_DNS+LwIP_DNS_Test();+#endif+         LED1(ON);       }       el      --- a/stm32f429_lwip_pro_list/2.stm32f429_lwip_basic_dhcp/Ur/lwipopts.h+++ b/stm32f429_lwip_pro_list/2.stm32f429_lwip_basic_dhcp/Ur/lwipopts.h@@ -121,6 +121,9 @@ a lot of data that needs to be copied, this should be t high. */    turning this on does currently not work. */ #define LWIP_DHCP 1 +/* ---------- DNS options ---------- */+#define LWIP_DNS                1+

编译成功后，验证结果截图如下：

3.dns_init主要流程

dns_init其实主要初始化了UDP，设置的默认DNS Server地址后面会被覆盖。

4.如何获取DNS Server地址

通过前一篇文章DHCP的学习，DNS Server的地址和本机IP地址会通过DHCP Server一起下发。在dhcp.c代码中看到dhcp_handle_ack解析DHCP Server的ACK报文时，会设置DNS Server IP地址，代码如下：

static voiddhcp_handle_ack(struct netif *netif){ ...#if LWIP_DNS  /* DNS rvers */  n = 0;  while(dhcp_option_given(dhcp, DHCP_OPTION_IDX_DNS_SERVER + n) && (n < DNS_MAX_SERVERS)) {     ip_addr_t dns_addr;    ip4_addr_t_u32(&dns_addr, htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_DNS_SERVER + n)));    dns_trver(n, &dns_addr);    n++;  }#endif /* LWIP_DNS */}

使用的Wireshark抓取的DHCP报文可以再次确认，如下：

在设备运行的Log中，我们也可以看到DNS Server IP地址就是DHCP ACK报文所提供的地址：(114.114.114.114, 53)

[19:33:07.252]ip_output_if: st0[19:33:07.253]IP header:[19:33:07.253]+-------------------------------+[19:33:07.254]| 4 | 5 |  0x00 |        56     | (v, hl, tos, len)[19:33:07.268]+-------------------------------+[19:33:07.268]|        2      |000|       0   | (id, flags, offt)[19:33:07.269]+-------------------------------+[19:33:07.280]|  255  |   17  |    0x0000     | (ttl, proto, chksum)[19:33:07.281]+-------------------------------+[19:33:07.281]|  192  |  168  |    1  |  102  | (src)[19:33:07.295]+-------------------------------+[19:33:07.295]|  114  |  114  |  114  |  114  | (dest)[19:33:07.296]+-------------------------------+

5. DNS域名解析流程

我们调用DNS API域名解析函数dns_gethostbyname后，解析流程大致如下：

6. DNS分析的设备Log

[19:33:07.232]开始DNS解析：www.qq.com[19:33:07.234]dns_enqueue: "www.qq.com": u DNS entry 0[19:33:07.248]dns_nd: dns_rvers[0] "www.qq.com": request[19:33:07.249]udp_connect: connected to 0.0.0.0,port 49153[19:33:07.250]udp_nd[19:33:07.250]udp_nd: added header in given pbuf 200045ec[19:33:07.250]udp_nd: nding datagram of length 36[19:33:07.250]udp_nd: UDP packet length 36[19:33:07.250]udp_nd: UDP checksum 0x0000[19:33:07.252]udp_nd: ip_output_if (,,,,IP_PROTO_UDP,)[19:33:07.252]ip_output_if: st0[19:33:07.253]IP header:[19:33:07.253]+-------------------------------+[19:33:07.254]| 4 | 5 |  0x00 |        56     | (v, hl, tos, len)[19:33:07.268]+-------------------------------+[19:33:07.268]|        2      |000|       0   | (id, flags, offt)[19:33:07.269]+-------------------------------+[19:33:07.280]|  255  |   17  |    0x0000     | (ttl, proto, chksum)[19:33:07.281]+-------------------------------+[19:33:07.281]|  192  |  168  |    1  |  102  | (src)[19:33:07.295]+-------------------------------+[19:33:07.295]|  114  |  114  |  114  |  114  | (dest)[19:33:07.296]+-------------------------------+[19:33:07.297]netif->output()ip_input: iphdr->dest 0x干贝怎么吃6601a8c0 netif->ip_addr 0x6601a8c0 (0x1a8c0, 0x1a8c0, 0x66000000)[19:33:07.309]ip_input: packet accepted on interface st[19:33:07.310]ip_input: [19:33:07.310]IP header:[19:33:07.310]+-------------------------------+[19:33:07.323]| 4 | 5 |  0x00 |        92     | (v, hl, tos, len)[19:33:07.323]+-------------------------------+[19:33:07.323]|        2      |000|       0   | (id, flags, offt)[19:33:07.339]+-------------------------------+[19:33:07.340]|  125  |   17  |    0x969c     | (ttl, proto, chksum)[19:33:07.340]+-------------------------------+[19:33:07.340]|  114  |  114  |  114  |  114  | (src)[19:33:07.342]+-------------------------------+[19:33:07.343]|  192  |  168  |    1  |  102  | (dest)[19:33:07.343]+-------------------------------+[19:33:07.358]ip_input: p->len 92 p->tot_len 92[19:33:07.358]udp_input: received datagram of length 72[19:33:07.358]UDP header:[19:33:07.358]+-------------------------------+[19:33:07.372]|        53     |     49153     | (src port, dest port)[19:33:07.372]+-------------------------------+[19:33:07.374]|        72     |     0x65fe    | (len, chksum)[19:33:07.374]+-------------------------------+[19:33:07.389]udp (192.168.1.102, 49153) <-- (114.114.114.114, 53)[19:33:07.390]pcb (0.0.0.0, 49153) --- (114.114.114.114, 53)[19:33:07.390]udp_input: calculating checksum[19:33:07.405]dns_recv: "www.qq.com": respon = 58.250.137.36[19:33:07.419][www.qq.com]域名解析的IP:58.250.137.36