DNS 解析调试(dig & nslookup)

Posted 2023-03-27

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参考技术A 最近在进行 dns 调试(比如开发了一个 dns 的 server,就需要调试dns 解析是否符合预期)的时候接触了一些基本工具.此处做个笔记,备查.

比较常用的是 A 和 CNAME

nslookup命令，是Linux里非常常用的网络命令，简而言之就是“查DNS信息用的”,如果没有此命令,通过 yum install bind-utils 进行安装.

nslookup是一个能够查询互联网域名服务器信息的程序。他有两种工作模式，即“交互模式”和“非交互模式”。

在“交互模式”下，用户可以向域名服务器查询各类主机、域名的信息，或者输出域名中的主机列表。

而在“非交互模式”下，用户可以针对一个主机或域名仅仅获取特定的名称或所需信息。

简单说下非交互模式

交互模式功能更加强大.

dig 全称 Domain Information Groper ,传言此工具非常强大.
废话不多说,直接上个例子,查询 www.baidu.com 在 8.8.8.8 服务器的 53 端口解析结果,当然如果要制定端口,增加 -p 53 或者你的端口即可.

从命令的返回结果看, dig 返回的信息更加丰富,调试中需要的可能还有 +trace 选项,用于追踪 dns 解析的全过程.比如

dig 普通的输出内容比较多,不便于查看,提供了几个简化的命令输出
+nocmd
+short
+nocomment
+nostat

使用dig查询dns解析

一般来说linux下查询域名解析有两种选择，nslookup或者dig，而在使用上我觉得dig更加方便顺手。
如果是在debian下的话，只要装上dnsutils这个包就可以使用dig命令了。

最基本的使用方式就是

dig www.oolec.com

即查询域名的A记录，查询的dns服务器将采用系统配置的服务器，即/etc/resovle.conf 中的。

如果要查询其他类型的记录，比如MX，CNAME，NS，PTR等，只需将类型加在命令后面即可

dig www.oolec.com mx
dig www.oolec.com ns

此外，如果你是一个系统管理员，部署好了一台dns服务器之后想对它进行解析测试，就必须要显式指定待测试的dns服务器地址了，例如

dig @202.106.0.20 www.oolec.com a

默认情况下dig将采用udp协议进行查询，如果要采用tcp方式，可以加上 +tcp参数

dig www.oolec.com a +tcp

另外一个重要的功能是+trace参数，使用这个参数之后将显示从根域逐级查询的过程

dig www.oolec.com a +trace

比如，对本站域名www.linuxers.cn A记录的trace查询可以看到根域.，顶级域.cn，以及linuxers.cn的域名权威服务器的地址及其各自的返回结果，这样对于追踪dns解析中的问题有很大的帮助。

[email protected]:~$ dig www.linuxers.cn a +trace
 
; <<>> DiG 9.5.1-P3 <<>> www.linuxers.cn a +trace
;; global options:  printcmd
.                       215857  IN      NS      E.ROOT-SERVERS.NET.
.                       215857  IN      NS      B.ROOT-SERVERS.NET.
.                       215857  IN      NS      J.ROOT-SERVERS.NET.
.                       215857  IN      NS      K.ROOT-SERVERS.NET.
.                       215857  IN      NS      L.ROOT-SERVERS.NET.
.                       215857  IN      NS      F.ROOT-SERVERS.NET.
.                       215857  IN      NS      G.ROOT-SERVERS.NET.
.                       215857  IN      NS      I.ROOT-SERVERS.NET.
.                       215857  IN      NS      M.ROOT-SERVERS.NET.
.                       215857  IN      NS      A.ROOT-SERVERS.NET.
.                       215857  IN      NS      C.ROOT-SERVERS.NET.
.                       215857  IN      NS      H.ROOT-SERVERS.NET.
.                       215857  IN      NS      D.ROOT-SERVERS.NET.
;; Received 228 bytes from 192.168.127.2#53(192.168.127.2) in 12 ms
 
cn.                     172800  IN      NS      a.dns.cn.
cn.                     172800  IN      NS      b.dns.cn.
cn.                     172800  IN      NS      c.dns.cn.
cn.                     172800  IN      NS      d.dns.cn.
cn.                     172800  IN      NS      e.dns.cn.
cn.                     172800  IN      NS      ns.cernet.net.
;; Received 298 bytes from 199.7.83.42#53(L.ROOT-SERVERS.NET) in 496 ms
 
linuxers.cn.            21600   IN      NS      ns1.dnspood.net.
linuxers.cn.            21600   IN      NS      ns2.dnspood.net.
;; Received 80 bytes from 202.112.0.44#53(ns.cernet.net) in 12 ms
 
www.linuxers.cn.        600     IN      A       218.240.42.72
;; Received 49 bytes from 222.186.26.115#53(ns2.dnspood.net) in 1132 ms

今天刚好是百度出问题时候。

关于dig的更进一步的使用方式请参考这里

dig (1) - BIND9

(Updated: Jun 30, 2000)

NAME

dig - DNS lookup utility

SYNOPSIS

dig [@server] [-b address] [-c class] [-f filename] [-k filename] [-m] [-p port#] [-q name] [-t type] [-x addr] [-y [hmac:]name:key] [-4] [-6] [name] [type] [class] [queryopt...]
dig [-h]
dig [global-queryopt...] [query...]

DESCRIPTION

dig (domain information groper) is a flexible tool for interrogating DNS name servers. It performs DNS lookups and displays the answers that are returned from the name server(s) that were queried. Most DNS administrators use dig

to troubleshoot DNS problems because of its flexibility, ease of use and clarity of output. Other lookup tools tend to have less functionality than dig.

Although digis normally used with command-line arguments, it also has a batch mode of operation for reading lookup requests from a file. A brief summary of its command-line arguments and options is printed when the -h option is given. Unlike earlier versions, the BIND 9 implementation of dig allows multiple lookups to be issued from the command line.

Unless it is told to query a specific name server, dig will try each of the servers listed in /etc/resolv.conf.

When no command line arguments or options are given, dig will perform an NS query for "." (the root).

It is possible to set per-user defaults for dig via ${HOME}/.digrc. This file is read and any options in it are applied before the command line arguments.

The IN and CH class names overlap with the IN and CH top level domains names. Either use the -t and -c options to specify the type and class, use the -q the specify the domain name, or use "IN." and "CH." when looking up these top level domains.

SIMPLE USAGE

A typical invocation of dig looks like:

 dig @server name type

where:

server

: is the name or IP address of the name server to query. This can be an IPv4 address in dotted-decimal notation or an IPv6 address in colon-delimited notation. When the supplied server argument is a hostname, dig resolves that name before querying that name server. If no server argument is provided, dig consults /etc/resolv.conf and queries the name servers listed there. The reply from the name server that responds is displayed.

name

: is the name of the resource record that is to be looked up.

type

: indicates what type of query is required --- ANY, A, MX, SIG, etc. type can be any valid query type. If no type argument is supplied, dig will perform a lookup for an A record.

OPTIONS

The -b option sets the source IP address of the query to address. This must be a valid address on one of the host‘s network interfaces or "0.0.0.0" or "::". An optional port may be specified by appending "#"

The default query class (IN for internet) is overridden by the -c option. class is any valid class, such as HS for Hesiod records or CH for Chaosnet records.

The -f option makes dig operate in batch mode by reading a list of lookup requests to process from the file filename. The file contains a number of queries, one per line. Each entry in the file should be organized in the same way they would be presented as queries to dig using the command-line interface.

The -m option enables memory usage debugging.

If a non-standard port number is to be queried, the -p option is used. port# is the port number that digwill send its queries instead of the standard DNS port number 53. This option would be used to test a name server that has been configured to listen for queries on a non-standard port number.

The -4 option forces dig to only use IPv4 query transport. The -6 option forces dig to only use IPv6 query transport.

The -t option sets the query type to type. It can be any valid query type which is supported in BIND 9. The default query type is "A", unless the -xoption is supplied to indicate a reverse lookup. A zone transfer can be requested by specifying a type of AXFR. When an incremental zone transfer (IXFR) is required, typeis set to ixfr=N. The incremental zone transfer will contain the changes made to the zone since the serial number in the zone‘s SOA record was N.

The -q option sets the query name to name. This useful do distinguish the name from other arguments.

Reverse lookups --- mapping addresses to names --- are simplified by the -x option. addris an IPv4 address in dotted-decimal notation, or a colon-delimited IPv6 address. When this option is used, there is no need to provide the name, class and type arguments. digautomatically performs a lookup for a name like 11.12.13.10.in-addr.arpa and sets the query type and class to PTR and IN respectively. By default, IPv6 addresses are looked up using nibble format under the IP6.ARPA domain. To use the older RFC1886 method using the IP6.INT domain specify the -i option. Bit string labels (RFC2874) are now experimental and are not attempted.

To sign the DNS queries sent by dig and their responses using transaction signatures (TSIG), specify a TSIG key file using the -k option. You can also specify the TSIG key itself on the command line using the -y option; hmac is the type of the TSIG, default HMAC-MD5, name is the name of the TSIG key and key is the actual key. The key is a base-64 encoded string, typically generated by dnssec-keygen(8). Caution should be taken when using the -y option on multi-user systems as the key can be visible in the output from ps(1) or in the shell‘s history file. When using TSIG authentication with dig, the name server that is queried needs to know the key and algorithm that is being used. In BIND, this is done by providing appropriate key and server statements in named.conf.

QUERY OPTIONS

digprovides a number of query options which affect the way in which lookups are made and the results displayed. Some of these set or reset flag bits in the query header, some determine which sections of the answer get printed, and others determine the timeout and retry strategies.

Each query option is identified by a keyword preceded by a plus sign (+). Some keywords set or reset an option. These may be preceded by the string no to negate the meaning of that keyword. Other keywords assign values to options like the timeout interval. They have the form +keyword=value. The query options are:

+[no]tcp

: Use [do not use] TCP when querying name servers. The default behavior is to use UDP unless an AXFR or IXFR query is requested, in which case a TCP connection is used.

+[no]vc

: Use [do not use] TCP when querying name servers. This alternate syntax to +[no]tcp is provided for backwards compatibility. The "vc" stands for "virtual circuit".

+[no]ignore

: Ignore truncation in UDP responses instead of retrying with TCP. By default, TCP retries are performed.

+domain=somename

: Set the search list to contain the single domain somename, as if specified in a domain directive in /etc/resolv.conf, and enable search list processing as if the +search option were given.

+[no]search

: Use [do not use] the search list defined by the searchlist or domain directive in resolv.conf (if any). The search list is not used by default.

+[no]showsearch

: Perform [do not perform] a search showing intermediate results.

+[no]defname

: Deprecated, treated as a synonym for +[no]search

+[no]aaonly

: Sets the "aa" flag in the query.

+[no]aaflag

: A synonym for +[no]aaonly.

+[no]adflag

: Set [do not set] the AD (authentic data) bit in the query. The AD bit currently has a standard meaning only in responses, not in queries, but the ability to set the bit in the query is provided for completeness.

+[no]cdflag

: Set [do not set] the CD (checking disabled) bit in the query. This requests the server to not perform DNSSEC validation of responses.

+[no]cl

: Display [do not display] the CLASS when printing the record.

+[no]ttlid

: Display [do not display] the TTL when printing the record.

+[no]recurse

: Toggle the setting of the RD (recursion desired) bit in the query. This bit is set by default, which means dig normally sends recursive queries. Recursion is automatically disabled when the +nssearchor +trace query options are used.

+[no]nssearch

: When this option is set, digattempts to find the authoritative name servers for the zone containing the name being looked up and display the SOA record that each name server has for the zone.

+[no]trace

: Toggle tracing of the delegation path from the root name servers for the name being looked up. Tracing is disabled by default. When tracing is enabled, digmakes iterative queries to resolve the name being looked up. It will follow referrals from the root servers, showing the answer from each server that was used to resolve the lookup.

+[no]cmd

: Toggles the printing of the initial comment in the output identifying the version of dig and the query options that have been applied. This comment is printed by default.

+[no]short

: Provide a terse answer. The default is to print the answer in a verbose form.

+[no]identify

: Show [or do not show] the IP address and port number that supplied the answer when the +shortoption is enabled. If short form answers are requested, the default is not to show the source address and port number of the server that provided the answer.

+[no]comments

: Toggle the display of comment lines in the output. The default is to print comments.

+[no]stats

: This query option toggles the printing of statistics: when the query was made, the size of the reply and so on. The default behavior is to print the query statistics.

+[no]qr

: Print [do not print] the query as it is sent. By default, the query is not printed.

+[no]question

: Print [do not print] the question section of a query when an answer is returned. The default is to print the question section as a comment.

+[no]answer

: Display [do not display] the answer section of a reply. The default is to display it.

+[no]authority

: Display [do not display] the authority section of a reply. The default is to display it.

+[no]additional

: Display [do not display] the additional section of a reply. The default is to display it.

+[no]all

: Set or clear all display flags.

+time=T

: Sets the timeout for a query to T seconds. The default timeout is 5 seconds. An attempt to set T to less than 1 will result in a query timeout of 1 second being applied.

+tries=T

: Sets the number of times to try UDP queries to server to T instead of the default, 3. If T is less than or equal to zero, the number of tries is silently rounded up to 1.

+retry=T

: Sets the number of times to retry UDP queries to server to T instead of the default, 2. Unlike +tries, this does not include the initial query.

+ndots=D

: Set the number of dots that have to appear in name to D for it to be considered absolute. The default value is that defined using the ndots statement in /etc/resolv.conf, or 1 if no ndots statement is present. Names with fewer dots are interpreted as relative names and will be searched for in the domains listed in the search or domain directive in /etc/resolv.conf.

+bufsize=B

: Set the UDP message buffer size advertised using EDNS0 to Bbytes. The maximum and minimum sizes of this buffer are 65535 and 0 respectively. Values outside this range are rounded up or down appropriately. Values other than zero will cause a EDNS query to be sent.

+edns=#

: Specify the EDNS version to query with. Valid values are 0 to 255. Setting the EDNS version will cause a EDNS query to be sent. +noedns clears the remembered EDNS version.

+[no]multiline

: Print records like the SOA records in a verbose multi-line format with human-readable comments. The default is to print each record on a single line, to facilitate machine parsing of the dig output.

+[no]fail

: Do not try the next server if you receive a SERVFAIL. The default is to not try the next server which is the reverse of normal stub resolver behavior.

+[no]besteffort

: Attempt to display the contents of messages which are malformed. The default is to not display malformed answers.

+[no]dnssec

: Requests DNSSEC records be sent by setting the DNSSEC OK bit (DO) in the OPT record in the additional section of the query.

+[no]sigchase

: Chase DNSSEC signature chains. Requires dig be compiled with -DDIG_SIGCHASE.

+trusted-key=####

Specifies a file containing trusted keys to be used with +sigchase. Each DNSKEY record must be on its own line.

If not specified dig will look for /etc/trusted-key.key then trusted-key.key in the current directory.

Requires dig be compiled with -DDIG_SIGCHASE.

+[no]topdown

: When chasing DNSSEC signature chains perform a top-down validation. Requires dig be compiled with -DDIG_SIGCHASE.

+[no]nsid

: Include an EDNS name server ID request when sending a query.

MULTIPLE QUERIES

The BIND 9 implementation of dig supports specifying multiple queries on the command line (in addition to supporting the -f batch file option). Each of those queries can be supplied with its own set of flags, options and query options.

In this case, each queryargument represent an individual query in the command-line syntax described above. Each consists of any of the standard options and flags, the name to be looked up, an optional query type and class and any query options that should be applied to that query.

A global set of query options, which should be applied to all queries, can also be supplied. These global query options must precede the first tuple of name, class, type, options, flags, and query options supplied on the command line. Any global query options (except the +[no]cmd option) can be overridden by a query-specific set of query options. For example:

dig +qr www.isc.org any -x 127.0.0.1 isc.org ns +noqr

shows how dig could be used from the command line to make three lookups: an ANY query for www.isc.org, a reverse lookup of 127.0.0.1 and a query for the NS records of isc.org. A global query option of +qr is applied, so that dig shows the initial query it made for each lookup. The final query has a local query option of +noqr which means that dig will not print the initial query when it looks up the NS records for isc.org.

IDN SUPPORT

If dig has been built with IDN (internationalized domain name) support, it can accept and display non-ASCII domain names. digappropriately converts character encoding of domain name before sending a request to DNS server or displaying a reply from the server. If you‘d like to turn off the IDN support for some reason, defines the IDN_DISABLE environment variable. The IDN support is disabled if the variable is set when dig runs.