OpenWrt之DNS設置
0.前言
本文不涉及smartdns、adguardhome、dns防污染等內容，只介紹DNS的設置
1.WAN口
保存&應用后 客戶機發出dns解析請求后路由器用上面的dns回應
2.Lan口
進入openwrt的luci頁面。在 網絡>網卡>LAN 選擇編輯
保存&應用后,路由器自身的dns解析請求 會使用 上面設置的DNS 來回應
3.LAN口DHCP選項
進入openwrt的luci頁面。在 網絡>網卡>LAN 選擇編輯
在 DHCP選項下 填入
6,223.5.5.5,119.29.29.29
效果如下：
該設置會修改連接到路由器LAN的DNS（類似於自定義電腦的DNS）
4.DHCP/DNS
5.總結
電腦DNS（LAN） > DHCP的DNS > WAN口DNS
1.最常用的DNS設置方式。可以由DHCP請求獲得，或自行設置。在靜態IP的情況下，必須設置，否則無法查詢外面的主機
2.如果路由器用於橋接方式，並且使用靜態IP時，無法用DHCP請求的方式得到DNS，這是該選項的主要用途。其他場合下，則會忽略由DHCP服務器的DNS設置，改用這個設置。
3.如果該機器是子網的DHCP服務器，用於設置DHCP客戶端的DNS。如果留空，默認則用自身的IP。通常客戶端看到的DNS是這個（手機，電腦等）
4.如果自己是子網的DNS服務器，用於設置轉發服務器。如果不設置，則用上游DNS（由1或2）服務器
當第2、3、4項不設置時，默認使用1的DNS解析
參考（Thanks）
https://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml#options
https://blog.csdn.net/weixin_41632560/article/details/89448612
https://www.right.com.cn/forum/thread-4059633-1-1.html
附錄.DHCP OPTION
以下是部分DHCP OPTION參照表
| DHCP OPTION | Meaing |
|---|---|
| 0 | None |
| 1 | 設置子網掩碼 |
| 2 | "Time Offset in Seconds from UTC |
| 3 | 設置網關 |
| 4 | N/4 Timeserver addresses |
| 5 | N/4 IEN-116 Server addresses |
| 6 | 設置DNS服務器 |
| 7 | N/4 Logging Server addresses |
| 8 | N/4 Quotes Server addresses |
| 9 | N/4 Printer Server addresses |
| 10 | N/4 Impress Server addresses |
| 11 | N/4 RLP Server addresses |
| 12 | 設置域名選項。 |
| 13 | Size of boot file in 512 byte chunks |
| 14 | Client to dump and name the file to dump it to |
| 15 | 設置域名后綴選項。 |
| 16 | Swap Server address |
| 17 | Path name for root disk |
| 18 | Path name for more BOOTP info |
| 19 | Enable/Disable IP Forwarding |
| 20 | Enable/Disable Source Routing |
| 21 | Routing Policy Filters |
| 22 | Max Datagram Reassembly Size |
| 23 | Default IP Time to Live |
| 24 | Path MTU Aging Timeout |
| 25 | Path MTU Plateau Table |
| 26 | Interface MTU Size |
| 27 | All Subnets are Local |
| 28 | Broadcast Address |
| 29 | Perform Mask Discovery |
| 30 | Provide Mask to Others |
| 31 | Perform Router Discovery |
| 32 | Router Solicitation Address |
| 33 | 設置靜態路由選項。該選項中包含一組有分類靜態路由（即目的地址的掩碼固定為自然掩碼，不能划分子網），客戶端收到該選項后，將在路由表中添加這些靜態路由。如果存在Option121，則忽略該選項。 |
| 34 | Trailer Encapsulation |
| 35 | ARP Cache Timeout |
| 36 | Ethernet Encapsulation |
| 37 | Default TCP Time to Live |
| 38 | TCP Keepalive Interval |
| 39 | TCP Keepalive Garbage |
| 40 | NIS Domain Name |
| 41 | NIS Server Addresses |
| 42 | NTP Server Addresses |
| 43 | Vendor Specific Information |
| 44 | 設置NetBios服務器選項。 |
| 45 | NETBIOS Datagram Distribution |
| 46 | 設置NetBios節點類型選項。 |
| 47 | NETBIOS Scope |
| 48 | X Window Font Server |
| 49 | X Window Display Manager |
| 50 | 設置請求IP選項。 |
| 51 | 設置IP地址租約時間選項。 |
| 52 | 設置Option附加選項。 |
| 53 | 設置DHCP消息類型。 |
| 54 | 設置服務器標識。 |
| 55 | 設置請求參數列表選項。客戶端利用該選項指明需要從服務器獲取哪些網絡配置參數。該選項內容為客戶端請求的參數對應的選項值。 |
| 56 | DHCP Error Message |
| 57 | DHCP Maximum Message Size |
| 58 | 設置續約T1時間，一般是租期時間的50%。 |
| 59 | 設置續約T2時間。一般是租期時間的87.5%。 |
| 60 | 設置廠商分類信息選項，用於標識DHCP客戶端的類型和配置。 |
| 61 | 設置客戶端標識選項。 |
| 62 | NetWare/IP Domain Name |
| 63 | NetWare/IP sub Options |
| 64 | NIS+ v3 Client Domain Name |
| 65 | NIS+ v3 Server Addresses |
| 66 | 設置TFTP服務器名選項，用來指定為客戶端分配的TFTP服務器的域名。 |
| 67 | 設置啟動文件名選項，用來指定為客戶端分配的啟動文件名。 |
| 68 | Home Agent Addresses |
| 69 | Simple Mail Server Addresses |
| 70 | Post Office Server Addresses |
| 71 | Network News Server Addresses |
| 72 | WWW Server Addresses |
| 73 | Finger Server Addresses |
| 74 | Chat Server Addresses |
| 75 | StreetTalk Server Addresses |
| 76 | ST Directory Assist. Addresses |
| 77 | 設置用戶類型標識。 |
| 78 | directory agent information |
| 79 | service location agent scope |
| 80 | Rapid Commit |
| 81 | Fully Qualified Domain Name |
| 82 | Relay Agent Information |
| 83 | Internet Storage Name Service |
| 85 | Novell Directory Services |
| 86 | Novell Directory Services |
| 87 | Novell Directory Services |
| 90 | Authentication |
| 93 | Client System Architecture |
| 94 | Client Network Device Interface |
| 95 | Lightweight Directory Access Protocol |
| 97 | UUID/GUID-based Client Identifier |
| 98 | Open Group's User Authentication |
| 100 | IEEE 1003.1 TZ String |
| 101 | Reference to the TZ Database |
| 108 | Number of seconds that DHCPv4 should be disabled |
| 109 | DHCPv4 over DHCPv6 Softwire Source Address Option |
| 112 | NetInfo Parent Server Address |
| 113 | NetInfo Parent Server Tag |
| 114 | DHCP Captive-Portal |
| 116 | DHCP Auto-Configuration |
| 117 | Name Service Search |
| 118 | Subnet Selection Option |
| 119 | DNS domain search list |
| 120 | SIP Servers DHCP Option |
| 121 | 設置無分類路由選項。該選項中包含一組無分類靜態路由（即目的地址的掩碼為任意值，可以通過掩碼來划分子網），客戶端收到該選項后，將在路由表中添加這些靜態路由。 |
| 122 | CableLabs Client Configuration |
| 123 | GeoConf Option |
| 124 | Vendor-Identifying Vendor Class |
| 125 | Vendor-Identifying Vendor-Specific Information |
| 138 | CAPWAP Access Controller addresses |
| 139 | a series of suboptions |
| 140 | a series of suboptions |
| 141 | List of domain names to search for SIP User Agent Configuration |
| 142 | ANDSF IPv4 Address Option for DHCPv4 |
| 143 | This option provides a list of URIs for SZTP bootstrap servers |
| 144 | Geospatial Location with Uncertainty |
| 145 | Forcerenew Nonce Capable |
| 146 | Information for selecting RDNSS |
| 147 | The name of the peer DOTS agent. |
| 148 | N/4 IPv4 addresses of peer DOTS agent(s). |
| 150 | 設置TFTP服務器地址選項，指定為客戶端分配的TFTP服務器的地址。 |
| 151 | Status code and optional N byte text message describing status. |
| 152 | "Absolute time (seconds since Jan 1, 1970) message was sent." |
| 153 | Number of seconds in the past when client entered current state. |
| 154 | "Absolute time (seconds since Jan 1, 1970) for beginning of query." |
| 155 | "Absolute time (seconds since Jan 1, 1970) for end of query." |
| 156 | State of IP address. |
| 157 | Indicates information came from local or remote server. |
| 158 | Includes one or multiple lists of PCP server IP addresses; each list is treated as a separate PCP server. |
| 159 | This option is used to configure a set of ports bound to a shared IPv4 address. |
| 160 | Previously assigned by [RFC7710]; known to also be used by Polycom. |
| 161 | Manufacturer Usage Descriptions |