文章目录
一、DNS域名系统
1.DNS作用
DNS（Domain Name System 的缩写）的作用非常简单。将域名和ip相互映射，一般用于域名解析，就是根据域名查出IP地址。
- DNS使用udp端口53；
- 域名的层级：域名由“.”进行划分，eg：
主机名.次级域名.顶级域名.根域名，最后一个“.”省略，默认由根管理； - 分级查询：输入一个网址（域名），首先会查找浏览器缓存，然后DNS服务器根据域名的层级，进行分级查询。dig命令的+trace参数可以显示DNS的整个分级查询过程。
- DNS的记录类型：dns有一些type类型，决定了dns报文的处理，如A记录、AAAA记录、CNAME记录、MX记录、NS记录、TXT记录、SRV记录、URL转发。
2.查找过程
虽然只需要返回一个IP地址，但是DNS的查询过程非常复杂，分成多个步骤。
工具软件dig可以显示整个查询过程。
root@ubuntu:~# dig www.baidu.com
# 第一部分：查询参数和统计
; <<>> DiG 9.10.3-P4-Ubuntu <<>> www.baidu.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 5575
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1
# 第二部分：查询内容
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.baidu.com. IN A
# 第三部分：DNS服务器的答复
# 显示www.baidu.com.有一个CNAME记录，以及www.a.shifen.com.有两个A记录
# 415、146是TTL值，表示缓存时间，即415s内不用重新查询
;; ANSWER SECTION:
www.baidu.com. 415 IN CNAME www.a.shifen.com.
www.a.shifen.com. 146 IN A 14.215.177.38
www.a.shifen.com. 146 IN A 14.215.177.39
# 第四部分：DNS服务器的一些传输信息
# 结果显示，本机DNS服务器是192.168.2.1，查询端口是53（DNS服务器默认端口），回应长度为101字节
;; Query time: 2 msec
;; SERVER: 192.168.2.1#53(192.168.2.1)
;; WHEN: Sat Apr 16 01:39:18 PDT 2022
;; MSG SIZE rcvd: 104
若不想看到这么多内容，可使用+short参数
root@ubuntu:~# dig www.baidu.com +short
www.a.shifen.com.
14.215.177.39
14.215.177.38
上面命令只返回www.baidu.com对应的2个IP地址（即A记录）。
本机只向自己的DNS服务器查询，dig命令有一个@参数，显示向其他DNS服务器查询的结果。
$ dig @4.2.2.2 www.baidu.com
上面命令指定向DNS服务器4.2.2.2查询。
3.其他DNS工具
（1）host 命令
host命令可以看作dig命令的简化版本，返回当前请求域名的各种记录。
$ host github.com
github.com has address 192.30.252.121
github.com mail is handled by 5 ALT2.ASPMX.L.GOOGLE.COM.
github.com mail is handled by 10 ALT4.ASPMX.L.GOOGLE.COM.
github.com mail is handled by 10 ALT3.ASPMX.L.GOOGLE.COM.
github.com mail is handled by 5 ALT1.ASPMX.L.GOOGLE.COM.
github.com mail is handled by 1 ASPMX.L.GOOGLE.COM.
$ host facebook.github.com
facebook.github.com is an alias for github.map.fastly.net.
github.map.fastly.net has address 103.245.222.133
host命令也可以用于逆向查询，即从IP地址查询域名，等同于dig -x 。
$ host 192.30.252.153
153.252.30.192.in-addr.arpa domain name pointer pages.github.com.
（2）nslookup 命令
nslookup命令用于互动式地查询域名记录。
root@ubuntu:~# nslookup www.baidu.com
Server: 192.168.2.1
Address: 192.168.2.1#53
Non-authoritative answer:
www.baidu.com canonical name = www.a.shifen.com.
Name: www.a.shifen.com
Address: 14.215.177.39
Name: www.a.shifen.com
Address: 14.215.177.38
学习一下从根域名解析ip的流程
root@ubuntu:~$ nslookup
> set type=ns #设置域名解析服务器记录 进行查看
> . #查看根域名服务记录
Server: 192.168.0.1
Address: 192.168.0.1#53
Non-authoritative answer: #中间缓存 不权威的
. nameserver = m.root-servers.net.
. nameserver = a.root-servers.net.
. nameserver = l.root-servers.net.
. nameserver = c.root-servers.net.
. nameserver = d.root-servers.net.
. nameserver = k.root-servers.net.
. nameserver = j.root-servers.net.
. nameserver = e.root-servers.net.
. nameserver = g.root-servers.net.
. nameserver = f.root-servers.net.
. nameserver = b.root-servers.net.
. nameserver = i.root-servers.net.
. nameserver = h.root-servers.net.
Authoritative answers can be found from:
a.root-servers.net internet address = 198.41.0.4
b.root-servers.net internet address = 199.9.14.201
c.root-servers.net internet address = 192.33.4.12
d.root-servers.net internet address = 199.7.91.13
e.root-servers.net internet address = 192.203.230.10
f.root-servers.net internet address = 192.5.5.241
g.root-servers.net internet address = 192.112.36.4
h.root-servers.net internet address = 198.97.190.53
i.root-servers.net internet address = 192.36.148.17
j.root-servers.net internet address = 192.58.128.30
k.root-servers.net internet address = 193.0.14.129
l.root-servers.net internet address = 199.7.83.42
m.root-servers.net internet address = 202.12.27.33
a.root-servers.net has AAAA address 2001:503:ba3e::2:30
b.root-servers.net has AAAA address 2001:500:200::b
> set type=a #设置类型为a 查找ip
> a.root-servers.net. #查看其中一个域名节点的ip
Server: 192.168.0.1
Address: 192.168.0.1#53
Non-authoritative answer:
Name: a.root-servers.net
Address: 198.41.0.4
> server 198.41.0.4 #设置域名服务器
Default server: 198.41.0.4
Address: 198.41.0.4#53
> set type=ns #查看根域名服务器
> com. #在根域名服务器下请求，查看会发现只会去我们设置的server进行
Server: 198.41.0.4
Address: 198.41.0.4#53
Non-authoritative answer:
*** Cant find com.: No answer
Authoritative answers can be found from:
com nameserver = a.gtld-servers.net.
com nameserver = b.gtld-servers.net.
com nameserver = c.gtld-servers.net.
com nameserver = d.gtld-servers.net.
com nameserver = e.gtld-servers.net.
com nameserver = f.gtld-servers.net.
com nameserver = g.gtld-servers.net.
com nameserver = h.gtld-servers.net.
com nameserver = i.gtld-servers.net.
com nameserver = j.gtld-servers.net.
com nameserver = k.gtld-servers.net.
com nameserver = l.gtld-servers.net.
com nameserver = m.gtld-servers.net.
a.gtld-servers.net internet address = 192.5.6.30
b.gtld-servers.net internet address = 192.33.14.30
c.gtld-servers.net internet address = 192.26.92.30
d.gtld-servers.net internet address = 192.31.80.30
e.gtld-servers.net internet address = 192.12.94.30
f.gtld-servers.net internet address = 192.35.51.30
g.gtld-servers.net internet address = 192.42.93.30
h.gtld-servers.net internet address = 192.54.112.30
i.gtld-servers.net internet address = 192.43.172.30
j.gtld-servers.net internet address = 192.48.79.30
k.gtld-servers.net internet address = 192.52.178.30
l.gtld-servers.net internet address = 192.41.162.30
m.gtld-servers.net internet address = 192.55.83.30
a.gtld-servers.net has AAAA address 2001:503:a83e::2:30
b.gtld-servers.net has AAAA address 2001:503:231d::2:30
> server 192.5.6.30
Default server: 192.5.6.30
Address: 192.5.6.30#53
> set type=ns #测试一个实际的域名
> bilibili.com
Server: 192.5.6.30
Address: 192.5.6.30#53
Non-authoritative answer:
*** Can't find bilibili.com: No answer
Authoritative answers can be found from:
bilibili.com nameserver = ns3.dnsv5.com.
bilibili.com nameserver = ns4.dnsv5.com.
ns3.dnsv5.com internet address = 129.211.176.212
ns3.dnsv5.com internet address = 162.14.18.188
ns3.dnsv5.com internet address = 162.14.24.251
ns3.dnsv5.com internet address = 162.14.25.251
ns3.dnsv5.com internet address = 18.194.2.137
ns3.dnsv5.com internet address = 183.192.201.94
ns3.dnsv5.com internet address = 223.166.151.16
ns3.dnsv5.com has AAAA address 2402:4e00:1430:1102:0:9136:2b2b:ba61
ns3.dnsv5.com internet address = 52.77.238.92
ns3.dnsv5.com internet address = 61.151.180.51
ns4.dnsv5.com internet address = 101.226.220.12
ns4.dnsv5.com internet address = 129.211.176.151
ns4.dnsv5.com internet address = 162.14.24.248
ns4.dnsv5.com internet address = 162.14.25.248
ns4.dnsv5.com internet address = 183.192.164.119
ns4.dnsv5.com internet address = 223.166.151.126
ns4.dnsv5.com has AAAA address 2402:4e00:1020:1264:0:9136:29b6:fc32
ns4.dnsv5.com internet address = 52.198.159.146
ns4.dnsv5.com internet address = 59.36.120.147
> server 129.211.176.212 #设置com对应的顶级域名服务器
Default server: 129.211.176.212
Address: 129.211.176.212#53
> set type=a #设置类型为a,查找对应ip
> www.bilibili.com. #查看ip，找到对应的内容分发域名
Server: 129.211.176.212
Address: 129.211.176.212#53
www.bilibili.com canonical name = b.w.bilicdn1.com.
> b.w.bilicdn1.com. #查看内容分发域名对应的ip，即是我们需要的ip
Server: 129.211.176.212
Address: 129.211.176.212#53
Name: b.w.bilicdn1.com
Address: 119.3.211.130
Name: b.w.bilicdn1.com
Address: 119.3.231.166
Name: b.w.bilicdn1.com
Address: 119.3.238.64
Name: b.w.bilicdn1.com
Address: 119.3.229.89
Name: b.w.bilicdn1.com
Address: 119.3.234.165
Name: b.w.bilicdn1.com
Address: 119.3.227.169
这里获得的ip就会返回给我们本地的dns服务器并且缓存，发送给我们浏览器输入域名时，对应的程序，用ip进行实际请求。
（3）whois 命令
whois命令用来查看域名的注册情况。
$ whois github.com
二、DNS实现
dns是基于udp实现的。
1.实现思路
参考udp的协议头以及dns的协议头，构造对应的头结构，对DNS服务器进行数据请求，要能正常获取到返回的ip。
receive（接收udp包）
===> decode_msg（解析数据包）
===> resolve_query（查表）
===> encode_msg（打包）
===> send（发回包）
2.测试思路
- 直接使用udp socket api进行数据请求，构造符合dns协议的结构数据即可；
- 解析收到的udp回复报文数据。获取到需要的ip即可。
三、两个开源DNS实现
1.dnspod-sr
#编译并运行
root@ubuntu:/root/dnspod-sr-master/src# ./dnspod-sr
[DBG:] dnspod-sr is successfully running now!!
[DBG:] max_ele_size is 1000000 - 1808
[DBG:] server may contain 332730 useful records
[DBG:] hash_table_size is 65536
[DBG:] we have 10 hash tables
[DBG:] we have 2 fetchers,2 quizzers
在另外一个环境上用dig命令进行测试，dns服务器有学习的功能
root@ubuntu:/home/root# dig @192.168.105.143 www.bilibili.com
; <<>> DiG 9.10.3-P4-Ubuntu <<>> @192.168.105.143 www.bilibili.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8662
;; flags: qr ra; QUERY: 1, ANSWER: 8, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;www.bilibili.com. IN A
;; ANSWER SECTION:
www.bilibili.com. 214 IN CNAME b.w.bilicdn1.com.
b.w.bilicdn1.com. 104 IN A 120.92.113.99
b.w.bilicdn1.com. 104 IN A 120.92.108.182
b.w.bilicdn1.com. 104 IN A 120.92.83.126
b.w.bilicdn1.com. 104 IN A 120.92.82.179
b.w.bilicdn1.com. 104 IN A 120.92.211.159
b.w.bilicdn1.com. 104 IN A 120.131.2.207
b.w.bilicdn1.com. 104 IN A 120.92.78.97
;; Query time: 2951 msec
;; SERVER: 192.168.105.143#53(192.168.105.143)
;; WHEN: Sat Dec 25 16:50:18 CST 2021
;; MSG SIZE rcvd: 173
使用dnsperf测试性能：
#安装dnsperf https://gitee.com/mirrors_DNS-OARC/dnsperf?_from=gitee_search
#注意按照第一种方式 版本包的安装，我用源码安装时有报错
#安装包下载地址https://www.dns-oarc.net/tools/dnsperf
tar -xvf dnsperf-2.9.0.tar.gz
cd dnsperf-2.9.0
./configure
make
make install
#写个配置文件 如下
root@ubuntu:/root/dnsperf-2.9.0# cat testfile
www.baidu.com A
www.bilibili.com A
#执行测试，可以分析结果
./src/dnsperf -d testfile -s 192.168.105.143 -c10000 -q10000 -l60
2.simpleDNS
下载：https://github.com/mwarning/SimpleDNS.git
启动该代码可执行文件，用dig请求进行查看：
#dig @192.168.105.143 -p 9000 foo.bar.com A
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8362
;; flags: qr; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;foo.bar.com. IN A
;; ANSWER SECTION:
foo.bar.com. 3600 IN A 192.168.1.1 #这个是测试代码中写死的域名（foo.bar.com）对应的ip
;; Query time: 0 msec
;; SERVER: 192.168.105.143#9000(192.168.105.143)
;; WHEN: Sat Dec 25 22:07:24 CST 2021
;; MSG SIZE rcvd: 56
四、dpdk-dns
1.思路
- 使用dpdk提供的接口，接管udp的数据，对dns相关的请求做协议处理；
- 参考simpleDNS逻辑，在已有的dpdk处理arp，udp， tcp的逻辑基础上，增加udp报文时，dns相关数据的处理；
- 参考simpleDNS中的逻辑进行业务处理返回。
2.开启KNI回发
kni能够进行tx将数据送回内核处理，但是却不能得到从内核中回环的数据，即kni进行rx时却收不到数据。这时需要进行回环的处理：
方法一：往“/sys/devices/virtual/net/%s/carrier”中写1，开启回环。
方法二：插入KNI模块的时候，将carrier设置为on
root@ubuntu:~/share# cd dpdk/
root@ubuntu:~/share/dpdk# cd x86_64-native-linux-gcc/kmod/
root@ubuntu:~/share/dpdk/x86_64-native-linux-gcc/kmod# ls
igb_uio.ko rte_kni.ko
root@ubuntu:~/share/dpdk/x86_64-native-linux-gcc/kmod# insmod rte_kni.ko carrier=on
方法三：代码中调用rte_kni_update_link，动态开启回发数据的功能。
3.dns数据的处理
if (UDP_PORT == ntohs(udp_hdr->dest_port))
{
#if ENABLE_DNS
g_src_ip = ip_hdr->dst_addr;
g_dest_ip == ip_hdr->src_addr;
g_src_port = ntohs(udp_hdr->dst_port);
g_dest_port = ntohs(udp_hdr->src_port);
rte_memcpy(g_dest_mac_addr, ehdr->s_addr.addr_bytes, RTE_ETHER_ADDR_LEN);
// udp userdata
uint16_t length = ntohs(udp_hdr->dgram_len);
uint16_t nbytes = length - sizeof(struct rte_udp_hdr);
uint8_t *data = (uint8_t *)(udp_hdr + 1);
// decode_msg
free_questions(msg.questions);
free_resource_records(msg.answers);
free_resource_records(msg.authorities);
free_resource_records(msg.additionals);
memset(&msg, 0, sizeof(struct Message));
decode_msg(&msg, data, nbytes);
// resolve_query
resolve_query(&msg);
// encode_msg
uint8_t *p = data;
encode_msg(&msg, &p);
// send_udp_pkt
int len = p - data;
do_send_udp(pktmbuf_pool, data, len);
