OpenWrt之DNS设置

0.前言

本文不涉及smartdns、adguardhome、dns防污染等内容，只介绍DNS的设置

1.WAN口

保存&应用后客户机发出dns解析请求后路由器用上面的dns回应

2.Lan口

进入openwrt的luci页面。在网络>网卡>LAN 选择编辑

保存&应用后,路由器自身的dns解析请求会使用上面设置的DNS 来回应

3.LAN口DHCP选项

进入openwrt的luci页面。在网络>网卡>LAN 选择编辑

在 DHCP选项下填入

6,223.5.5.5,119.29.29.29

效果如下：

该设置会修改连接到路由器LAN的DNS（类似于自定义电脑的DNS）

4.DHCP/DNS

5.总结

电脑DNS（LAN） > DHCP的DNS > WAN口DNS

1.最常用的DNS设置方式。可以由DHCP请求获得，或自行设置。在静态IP的情况下，必须设置，否则无法查询外面的主机

2.如果路由器用于桥接方式，并且使用静态IP时，无法用DHCP请求的方式得到DNS，这是该选项的主要用途。其他场合下，则会忽略由DHCP服务器的DNS设置，改用这个设置。

3.如果该机器是子网的DHCP服务器，用于设置DHCP客户端的DNS。如果留空，默认则用自身的IP。通常客户端看到的DNS是这个（手机，电脑等）

4.如果自己是子网的DNS服务器，用于设置转发服务器。如果不设置，则用上游DNS（由1或2）服务器

当第2、3、4项不设置时，默认使用1的DNS解析

参考（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

附录.DHCP OPTION

以下是部分DHCP OPTION参照表

DHCP OPTION	Meaing
0	None
1	设置子网掩码
2	"Time Offset in Seconds from UTC
3	设置网关
4	N/4 Timeserver addresses
5	N/4 IEN-116 Server addresses
6	设置DNS服务器
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	设置域名选项。
13	Size of boot file in 512 byte chunks
14	Client to dump and name the file to dump it to
15	设置域名后缀选项。
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	设置静态路由选项。该选项中包含一组有分类静态路由（即目的地址的掩码固定为自然掩码，不能划分子网），客户端收到该选项后，将在路由表中添加这些静态路由。如果存在Option121，则忽略该选项。
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	设置NetBios服务器选项。
45	NETBIOS Datagram Distribution
46	设置NetBios节点类型选项。
47	NETBIOS Scope
48	X Window Font Server
49	X Window Display Manager
50	设置请求IP选项。
51	设置IP地址租约时间选项。
52	设置Option附加选项。
53	设置DHCP消息类型。
54	设置服务器标识。
55	设置请求参数列表选项。客户端利用该选项指明需要从服务器获取哪些网络配置参数。该选项内容为客户端请求的参数对应的选项值。
56	DHCP Error Message
57	DHCP Maximum Message Size
58	设置续约T1时间，一般是租期时间的50%。
59	设置续约T2时间。一般是租期时间的87.5%。
60	设置厂商分类信息选项，用于标识DHCP客户端的类型和配置。
61	设置客户端标识选项。
62	NetWare/IP Domain Name
63	NetWare/IP sub Options
64	NIS+ v3 Client Domain Name
65	NIS+ v3 Server Addresses
66	设置TFTP服务器名选项，用来指定为客户端分配的TFTP服务器的域名。
67	设置启动文件名选项，用来指定为客户端分配的启动文件名。
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	设置用户类型标识。
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	设置无分类路由选项。该选项中包含一组无分类静态路由（即目的地址的掩码为任意值，可以通过掩码来划分子网），客户端收到该选项后，将在路由表中添加这些静态路由。
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	设置TFTP服务器地址选项，指定为客户端分配的TFTP服务器的地址。
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