dnsc

Submit query against a list of DNS servers and display summary of results

Table of Contents

• Project home
• Overview
• Features
  • Current
  • Planned
• Changelog
• Requirements
  • Building source code
  • Running
• Installation
  • From source
  • Using release binaries
• Configuration
  • Precedence
  • Query types supported
  • Service Location (SRV) Protocol "shortcuts"
  • Command-line arguments
  • Configuration file
• Examples
  • Our config file
  • Flags only, no config file
  • Use config file for DNS servers list and query types
  • Specify DNS servers list via flags
  • Query nameserver record (NS)
  • Query pointer record (PTR) using IP Address
  • Query server record (SRV)
  • Query server record (SRV) using SRV protocol keyword (aka, "shortcut")
  • Force exit on first DNS error
  • Use single-line summary output format
• Inspiration
• References

Project home

See our GitHub repo for the latest code, to file an issue or submit improvements for review and potential inclusion into the project.

Overview

Run a DNS query concurrently against all servers in a list and provide summary of results. This is most useful after moving servers between subnets when an IP Address change is expected, but where the change may not have propagated between all DNS servers. The summary output is useful for spotting systems lagging behind the others.

Command-line flags are supported for all options, though for some settings (e.g., DNS servers), specifying values via configuration file is easier for repeat use.

Features

Current

• A mix of command-line flags and configuration file options may be used for all options

• Query just one server or as many as are provided

  • Note: A configuration file is recommended for providing multiple DNS servers

• Multiple query types supported

• Multiple Service Location (SRV) Protocol "shortcuts" supported

• User configurable logging levels

• User configurable logging format

• User configurable results summary output format

• User configurable query timeout

Planned

See our GitHub repo for planned future work.

Changelog

See the CHANGELOG.md file for the changes associated with each release of this application. Changes that have been merged to master, but not yet an official release may also be noted in the file under the Unreleased section. A helpful link to the Git commit history since the last official release is also provided for further review.

Requirements

The following is a loose guideline. Other combinations of Go and operating systems for building and running tools from this repo may work, but have not been tested.

Building source code

• Go
  • see this project's go.mod file for preferred version
  • this project tests against officially supported Go releases
    • the most recent stable release (aka, "stable")
    • the prior, but still supported release (aka, "oldstable")
• GCC
  • if building with custom options (as the provided Makefile does)
• make
  • if using the provided Makefile

Running

• Windows 10
• Ubuntu Linux 18.04+
• Red Hat Enterprise Linux 7+

Installation

From source

1. Download Go
2. Install Go
3. Clone the repo
   1. cd /tmp
   2. git clone https://github.com/atc0005/dnsc
   3. cd dnsc
4. Install dependencies (optional)
   • for Ubuntu Linux
     • sudo apt-get install make gcc
   • for CentOS Linux
     1. sudo yum install make gcc
5. Build
   • for current operating system
     • go build -mod=vendor ./cmd/dnsc/
       • forces build to use bundled dependencies in top-level vendor folder
   • for all supported platforms (where make is installed)
     • make all
   • for Windows
     • make windows
   • for Linux
     • make linux
6. Copy the applicable binary to whatever systems needs to run it
   • if using Makefile: look in /tmp/dnsc/release_assets/dnsc/
   • if using go build: look in /tmp/dnsc/

NOTE: Depending on which Makefile recipe you use the generated binary may be compressed and have an xz extension. If so, you should decompress the binary first before deploying it (e.g., xz -d dnsc-linux-amd64.xz).

Using release binaries

1. Download the latest release binaries
2. Decompress binaries
   • e.g., xz -d dnsc-linux-amd64.xz
3. Deploy
   • Place dnsc in a location of your choice
     • e.g., /usr/local/bin/

NOTE:

DEB and RPM packages are provided as an alternative to manually deploying binaries.

Configuration

Precedence

The priority order is:

1. Command line flags (highest priority)
2. Configuration file
3. Default settings (lowest priority)

The intent of this behavior is to provide a feathered layering of configuration settings; if a configuration file provides nearly all settings that you want, specify just the settings that you wish to override via command-line flags and use the configuration file for the other settings.

Query types supported

These are the record types currently supported:

• CNAME
• A
• AAAA
• MX
• NS
• PTR
• SRV

Other types will be added as I encounter a need for them, or as requested.

Service Location (SRV) Protocol "shortcuts"

These are the keywords currently supported along with an example of the query string used for a user-provided query string of example.com. Others will be added as I encounter a need for them, or as requested.

These "shortcuts" are entirely optional. For example, you may still specify the srv query type and provide the _ldap._tcp.dc._msdcs.example.com query string manually to get the same effect.

User-specified query string	Keyword	Query string submitted to servers
example.com	msdcs	_ldap._tcp.dc._msdcs.example.com
example.com	kerberos	_kerberos._tcp.example.com
example.com	xmppsrv	_xmpp-server._tcp.example.com
example.com	xmppclient	_xmpp-client._tcp.example.com
example.com	sip	_sip._tcp.example.com

Command-line arguments

• Flags marked as required must be set via CLI flag or within a TOML-formatted configuration file.
• Flags not marked as required are for settings where a useful default is already defined.

Flag	Required	Default	Repeat	Possible	Description
h, help	No	false	No	h, help	Show Help text along with the list of supported flags.
ds, dns-server	Yes	empty string	Yes	one valid IP Address per flag invocation	DNS server to submit query against. This flag may be repeated for each additional DNS server to query.
cf, config-file	Yes	empty string	No	valid file name characters	Full path to TOML-formatted configuration file. See config.example.toml for a starter template.
v, version	No	false	No	v, version	Whether to display application version and then immediately exit application.
def, dns-errors-fatal	No	false	No	def, dns-errors-fatal	Whether DNS-related errors should force this application to immediately exit.
ot, omit-timestamp	No	false	No	ot, omit-timestamp	Whether the date & time for when the output is generated is omitted from the results output.
q, query	Yes	empty string	No	any valid FQDN string	Fully-qualified system to lookup from all provided DNS servers.
sp, srv-protocol	No	empty list	Yes	supported keywords	Service Location (SRV) protocols associated with a given domain name as the query string. For example, msdcs can be specified as the SRV record protocol along with example.com as the query string to search DNS for _ldap._tcp.dc._msdcs.example.com. This flag may be repeated for each additional SRV protocol that you wish to request records for.
ll, log-level	No	info	No	fatal, error, warn, info, debug	Log message priority filter. Log messages with a lower level are ignored.
lf, log-format	No	text	No	cli, json, logfmt, text, discard	Use the specified apex/log package "handler" to output log messages in that handler's format.
ro, results-output	No	multi-line	No	multi-line, single-line	Specifies whether the results summary output is composed of a single comma-separated line of records for a query, or whether the records are returned one per line.
t, type	No	A	Yes	supported types	DNS query type to use when submitting a DNS query to each provided server. This flag may be repeated for each additional DNS record type you wish to request.
to, timeout	No	10	No	any positive whole number	Maximum number of seconds allowed for a DNS query to take before timing out.

Configuration file

Configuration file settings have the lowest priority and are overridden by settings specified in other configuration sources, except for default values. See the Command-line Arguments table for more information, including the available values for the listed configuration settings.

Flag Name	Config file Setting Name	Notes
dns-server	dns_servers	Multi-line array
query	query	While supported, having a fixed query in the config file is not a normal use case.
dns-errors-fatal	dns_errors_fatal	Opt-in setting. Useful to leave as-is for most use cases.
log-level	log_level
log-format	log_format
results-output	results_output
omit-timestamp	omit_timestamp
type	dns_request_types	Multi-line array
srv-protocol	dns_srv_protocols	Multi-line array
timeout	timeout

The config.example.toml file is intended as a starting point for your own config.toml configuration file and attempts to illustrate working values for the available command-line flags.

Once reviewed and potentially adjusted, your copy of the config.toml file can be placed in one of the following locations to be automatically detected and used by this application:

• alongside the dnsc (or dnsc.exe) binary (as config.toml)
• at $HOME/.config/dnsc/config.toml on a UNIX-like system (e.g., Linux distro, Mac)
• at C:\Users\YOUR_USERNAME\AppData\dnsc\config.toml on a Windows system

Feel free to place the file wherever you like and refer to it using the -cf (short flag name) or -config-file (full-length flag name). See the Examples and Command-line arguments sections for usage details.

Examples

Our config file

These examples assume that the referenced config.example.toml file has the following contents:

dns_servers = [

    # https://developers.google.com/speed/public-dns
    "8.8.8.8",
    "8.8.4.4",

    # https://www.opendns.com/setupguide/
    "208.67.222.222",
    "208.67.220.220",

    # https://blog.cloudflare.com/announcing-1111/
    "1.1.1.1",
]

dns_query_types = [
    "A",
    "AAAA",
    "MX",
    "NS",
    "CNAME",
]

results_output = "multi-line"

See the Configuration file section for additional information, including supported locations for this file.

Flags only, no config file

Here the dnsc application attempted to load a config file using the locations mentioned in the Configuration file section, but one was not found:

$ dnsc -ds 8.8.8.8 -ds 8.8.4.4 -ds 208.67.220.220 -ds 208.67.222.222 -q www.yahoo.com
  INFO[0000] User-specified config file not provided
  INFO[0000] Trying to load config file "/mnt/t/github/dnsc/config.toml"
  WARN[0000] Config file "/mnt/t/github/dnsc/config.toml" not found or unable to load
  INFO[0000] Trying to load config file "/home/ubuntu/.config/dnsc/config.toml"
  WARN[0000] Config file "/home/ubuntu/.config/dnsc/config.toml" not found or unable to load
  WARN[0000] Failed to load config files, relying only on provided flag settings


Server            RTT     Query            Query Type    Answer                          Answer Type    TTL
---               ---     ---              ---           ---                             ---            ---
208.67.220.220    20ms    www.yahoo.com    A             new-fp-shed.wg1.b.yahoo.com.    CNAME          21
208.67.220.220    20ms    www.yahoo.com    A             74.6.143.25                     A              33
208.67.220.220    20ms    www.yahoo.com    A             74.6.143.26                     A              33
208.67.220.220    20ms    www.yahoo.com    A             74.6.231.20                     A              33
208.67.220.220    20ms    www.yahoo.com    A             74.6.231.21                     A              33
208.67.222.222    20ms    www.yahoo.com    A             new-fp-shed.wg1.b.yahoo.com.    CNAME          54
208.67.222.222    20ms    www.yahoo.com    A             74.6.143.25                     A              29
208.67.222.222    20ms    www.yahoo.com    A             74.6.143.26                     A              29
208.67.222.222    20ms    www.yahoo.com    A             74.6.231.20                     A              29
208.67.222.222    20ms    www.yahoo.com    A             74.6.231.21                     A              29
8.8.4.4           7ms     www.yahoo.com    A             new-fp-shed.wg1.b.yahoo.com.    CNAME          36
8.8.4.4           7ms     www.yahoo.com    A             74.6.143.25                     A              45
8.8.4.4           7ms     www.yahoo.com    A             74.6.143.26                     A              45
8.8.4.4           7ms     www.yahoo.com    A             74.6.231.20                     A              45
8.8.4.4           7ms     www.yahoo.com    A             74.6.231.21                     A              45
8.8.8.8           8ms     www.yahoo.com    A             new-fp-shed.wg1.b.yahoo.com.    CNAME          25
8.8.8.8           8ms     www.yahoo.com    A             74.6.143.25                     A              22
8.8.8.8           8ms     www.yahoo.com    A             74.6.143.26                     A              22
8.8.8.8           8ms     www.yahoo.com    A             74.6.231.20                     A              22
8.8.8.8           8ms     www.yahoo.com    A             74.6.231.21                     A              22

Since we did not specify a record query type, only A records were requested in the query to each DNS server. Since we have recursion enabled and the dnsc application does not exclude them, the initial CNAME record found by each query is also listed in the Answers section above for each DNS server that had it.

Use config file for DNS servers list and query types

As can be seen below, this example produces quite a bit of output.

$ dnsc --config-file ./config.example.toml -q www.yahoo.com
  INFO[0000] User-specified config file provided, will attempt to load it
  INFO[0000] Trying to load config file "./config.example.toml"
  INFO[0000] Config file successfully loaded config_file=./config.example.toml


Server            RTT     Query            Type     Answers                         TTL
---               ---     ---              ---      ---                             ---
1.1.1.1           7ms     www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    8
1.1.1.1           7ms     www.yahoo.com    A        74.6.143.25                     8
1.1.1.1           7ms     www.yahoo.com    A        74.6.143.26                     8
1.1.1.1           7ms     www.yahoo.com    A        74.6.231.20                     8
1.1.1.1           7ms     www.yahoo.com    A        74.6.231.21                     8
1.1.1.1           51ms    www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    60
1.1.1.1           7ms     www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    12
1.1.1.1           7ms     www.yahoo.com    AAAA     2001:4998:124:1507::f000        12
1.1.1.1           7ms     www.yahoo.com    AAAA     2001:4998:124:1507::f001        12
1.1.1.1           7ms     www.yahoo.com    AAAA     2001:4998:44:3507::8000         12
1.1.1.1           7ms     www.yahoo.com    AAAA     2001:4998:44:3507::8001         12
1.1.1.1           73ms    www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    60
208.67.220.220    21ms    www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    19
208.67.220.220    21ms    www.yahoo.com    AAAA     2001:4998:44:3507::8001         16
208.67.220.220    21ms    www.yahoo.com    AAAA     2001:4998:124:1507::f000        16
208.67.220.220    21ms    www.yahoo.com    AAAA     2001:4998:124:1507::f001        16
208.67.220.220    21ms    www.yahoo.com    AAAA     2001:4998:44:3507::8000         16
208.67.220.220    23ms    www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    42
208.67.220.220    22ms    www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    20
208.67.220.220    22ms    www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    19
208.67.220.220    22ms    www.yahoo.com    A        74.6.143.25                     58
208.67.220.220    22ms    www.yahoo.com    A        74.6.143.26                     58
208.67.220.220    22ms    www.yahoo.com    A        74.6.231.20                     58
208.67.220.220    22ms    www.yahoo.com    A        74.6.231.21                     58
208.67.222.222    22ms    www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    25
208.67.222.222    22ms    www.yahoo.com    A        74.6.143.25                     50
208.67.222.222    22ms    www.yahoo.com    A        74.6.143.26                     50
208.67.222.222    22ms    www.yahoo.com    A        74.6.231.20                     50
208.67.222.222    22ms    www.yahoo.com    A        74.6.231.21                     50
208.67.222.222    21ms    www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    19
208.67.222.222    21ms    www.yahoo.com    AAAA     2001:4998:44:3507::8001         16
208.67.222.222    21ms    www.yahoo.com    AAAA     2001:4998:124:1507::f000        16
208.67.222.222    21ms    www.yahoo.com    AAAA     2001:4998:124:1507::f001        16
208.67.222.222    21ms    www.yahoo.com    AAAA     2001:4998:44:3507::8000         16
208.67.222.222    21ms    www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    20
208.67.222.222    23ms    www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    19
8.8.4.4           7ms     www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    34
8.8.4.4           8ms     www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    52
8.8.4.4           8ms     www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    34
8.8.4.4           8ms     www.yahoo.com    AAAA     2001:4998:44:3507::8001         1
8.8.4.4           8ms     www.yahoo.com    AAAA     2001:4998:124:1507::f000        1
8.8.4.4           8ms     www.yahoo.com    AAAA     2001:4998:44:3507::8000         1
8.8.4.4           8ms     www.yahoo.com    AAAA     2001:4998:124:1507::f001        1
8.8.4.4           7ms     www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    33
8.8.4.4           7ms     www.yahoo.com    A        74.6.143.25                     3
8.8.4.4           7ms     www.yahoo.com    A        74.6.143.26                     3
8.8.4.4           7ms     www.yahoo.com    A        74.6.231.20                     3
8.8.4.4           7ms     www.yahoo.com    A        74.6.231.21                     3
8.8.8.8           7ms     www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    34
8.8.8.8           7ms     www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    27
8.8.8.8           7ms     www.yahoo.com    AAAA     2001:4998:124:1507::f000        9
8.8.8.8           7ms     www.yahoo.com    AAAA     2001:4998:124:1507::f001        9
8.8.8.8           7ms     www.yahoo.com    AAAA     2001:4998:44:3507::8000         9
8.8.8.8           7ms     www.yahoo.com    AAAA     2001:4998:44:3507::8001         9
8.8.8.8           7ms     www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    52
8.8.8.8           7ms     www.yahoo.com    A        74.6.143.25                     1
8.8.8.8           7ms     www.yahoo.com    A        74.6.143.26                     1
8.8.8.8           7ms     www.yahoo.com    A        74.6.231.20                     1
8.8.8.8           7ms     www.yahoo.com    A        74.6.231.21                     1
8.8.8.8           7ms     www.yahoo.com    CNAME    new-fp-shed.wg1.b.yahoo.com.    52

Specify DNS servers list via flags

You can also specify the DNS servers via CLI flags, though it is a bit more verbose:

$ dnsc -ds 8.8.8.8 -ds 8.8.4.4 -ds 208.67.220.220 -ds 208.67.222.222 -q www.yahoo.com
  INFO[0000] User-specified config file not provided
  INFO[0000] Trying to load config file "/mnt/t/github/dnsc/config.toml"
  WARN[0000] Config file "/mnt/t/github/dnsc/config.toml" not found or unable to load
  INFO[0000] Trying to load config file "/home/ubuntu/.config/dnsc/config.toml"
  WARN[0000] Config file "/home/ubuntu/.config/dnsc/config.toml" not found or unable to load
  WARN[0000] Failed to load config files, relying only on provided flag settings


Server            RTT     Query            Query Type    Answer                          Answer Type    TTL
---               ---     ---              ---           ---                             ---            ---
208.67.220.220    20ms    www.yahoo.com    A             new-fp-shed.wg1.b.yahoo.com.    CNAME          43
208.67.220.220    20ms    www.yahoo.com    A             74.6.143.25                     A              48
208.67.220.220    20ms    www.yahoo.com    A             74.6.143.26                     A              48
208.67.220.220    20ms    www.yahoo.com    A             74.6.231.20                     A              48
208.67.220.220    20ms    www.yahoo.com    A             74.6.231.21                     A              48
208.67.222.222    20ms    www.yahoo.com    A             new-fp-shed.wg1.b.yahoo.com.    CNAME          54
208.67.222.222    20ms    www.yahoo.com    A             74.6.143.24                     A              42
208.67.222.222    20ms    www.yahoo.com    A             74.6.231.19                     A              42
8.8.4.4           7ms     www.yahoo.com    A             new-fp-shed.wg1.b.yahoo.com.    CNAME          44
8.8.4.4           7ms     www.yahoo.com    A             74.6.143.25                     A              44
8.8.4.4           7ms     www.yahoo.com    A             74.6.143.26                     A              44
8.8.4.4           7ms     www.yahoo.com    A             74.6.231.20                     A              44
8.8.4.4           7ms     www.yahoo.com    A             74.6.231.21                     A              44
8.8.8.8           7ms     www.yahoo.com    A             new-fp-shed.wg1.b.yahoo.com.    CNAME          44
8.8.8.8           7ms     www.yahoo.com    A             74.6.143.25                     A              44
8.8.8.8           7ms     www.yahoo.com    A             74.6.143.26                     A              44
8.8.8.8           7ms     www.yahoo.com    A             74.6.231.20                     A              44
8.8.8.8           7ms     www.yahoo.com    A             74.6.231.21                     A              44

No errors here since www.yahoo.com had records for all of the requested query types.

Query nameserver record (NS)

Here we query the Google Public DNS server 8.8.8.8 for the nameserver (NS) records for the google.com domain.

$ dnsc --ds 8.8.8.8 -q google.com -t ns


Server     RTT     Query         Type    Answer             Answer Type    TTL
---        ---     ---           ---     ---                ---            ---
8.8.8.8    77ms    google.com    NS      ns3.google.com.    NS             21600
8.8.8.8    77ms    google.com    NS      ns2.google.com.    NS             21600
8.8.8.8    77ms    google.com    NS      ns4.google.com.    NS             21600
8.8.8.8    77ms    google.com    NS      ns1.google.com.    NS             21600

Query Performed: 2022-06-01T06:30:32-05:00

Query pointer record (PTR) using IP Address

Not shown is the initial query for www.yahoo.com which resolved to multiple A records. I picked one of the IP Addresses from the list and used it in the example below.

$ dnsc --ds 8.8.8.8 --q 74.6.143.25 -t ptr
  INFO[0000] User-specified config file not provided
  INFO[0000] Trying to load config file "/mnt/t/github/dnsc/config.toml"
  WARN[0000] Config file "/mnt/t/github/dnsc/config.toml" not found or unable to load
  INFO[0000] Trying to load config file "/home/ubuntu/.config/dnsc/config.toml"
  WARN[0000] Config file "/home/ubuntu/.config/dnsc/config.toml" not found or unable to load
  WARN[0000] Failed to load config files, relying only on provided flag settings


Server     RTT    Query          Query Type    Answer                                             Answer Type    TTL
---        ---    ---            ---           ---                                                ---            ---
8.8.8.8    7ms    74.6.143.25    PTR           media-router-fp73.prod.media.vip.bf1.yahoo.com.    PTR            186

Query server record (SRV)

In this example, we query for available XMPP servers for conversations.im.

$ dnsc --ds 8.8.8.8 --q "_xmpp-client._tcp.conversations.im" -t srv
  INFO[0000] User-specified config file not provided
  INFO[0000] Trying to load config file "/mnt/t/github/dnsc/config.toml"
  WARN[0000] Config file "/mnt/t/github/dnsc/config.toml" not found or unable to load
  INFO[0000] Trying to load config file "/home/ubuntu/.config/dnsc/config.toml"
  WARN[0000] Config file "/home/ubuntu/.config/dnsc/config.toml" not found or unable to load
  WARN[0000] Failed to load config files, relying only on provided flag settings


Server     RTT    Query                                 Query Type    Answer                     Answer Type    TTL
---        ---    ---                                   ---           ---                        ---            ---
8.8.8.8    7ms    _xmpp-client._tcp.conversations.im    SRV           xmpp.conversations.im.     SRV            2533
8.8.8.8    7ms    _xmpp-client._tcp.conversations.im    SRV           xmpps.conversations.im.    SRV            2533

Query server record (SRV) using SRV protocol keyword (aka, "shortcut")

In this example, we query for available XMPP servers for conversations.im using a SRV protocol keyword or "shortcut". This makes the query a little less verbose to type. You may optionally omit -t srv from this example and you will receive the same result; if specifying a SRV protocol keyword, this application assumes that you wish to submit a SRV record query.

$ dnsc --ds 8.8.8.8 --q "conversations.im" -sp "xmppclient" -t srv
  INFO[0000] User-specified config file not provided
  INFO[0000] Trying to load config file "/mnt/t/github/dnsc/config.toml"
  WARN[0000] Config file "/mnt/t/github/dnsc/config.toml" not found or unable to load
  INFO[0000] Trying to load config file "/home/ubuntu/.config/dnsc/config.toml"
  WARN[0000] Config file "/home/ubuntu/.config/dnsc/config.toml" not found or unable to load
  WARN[0000] Failed to load config files, relying only on provided flag settings


Server     RTT    Query                                 Query Type    Answer                     Answer Type    TTL
---        ---    ---                                   ---           ---                        ---            ---
8.8.8.8    8ms    _xmpp-client._tcp.conversations.im    SRV           xmpps.conversations.im.    SRV            2837
8.8.8.8    8ms    _xmpp-client._tcp.conversations.im    SRV           xmpp.conversations.im.     SRV            2837

As with other record/query types, you may also mix several together. Here we specify the SRV protocol as before, but leave out the explicit -t srv (relying on implicit inclusion) and also specify that we wish to query for available A records.

$ dnsc --ds 8.8.8.8 --q "conversations.im" -sp "xmppclient" -t a
  INFO[0000] User-specified config file not provided
  INFO[0000] Trying to load config file "/mnt/t/github/dnsc/config.toml"
  WARN[0000] Config file "/mnt/t/github/dnsc/config.toml" not found or unable to load
  INFO[0000] Trying to load config file "/home/ubuntu/.config/dnsc/config.toml"
  WARN[0000] Config file "/home/ubuntu/.config/dnsc/config.toml" not found or unable to load
  WARN[0000] Failed to load config files, relying only on provided flag settings


Server     RTT      Query                                 Query Type    Answer                     Answer Type    TTL
---        ---      ---                                   ---           ---                        ---            ---
8.8.8.8    27ms     _xmpp-client._tcp.conversations.im    SRV           xmpp.conversations.im.     SRV            3599
8.8.8.8    27ms     _xmpp-client._tcp.conversations.im    SRV           xmpps.conversations.im.    SRV            3599
8.8.8.8    231ms    conversations.im                      A             78.47.177.120              A              3599

Force exit on first DNS error

As of v0.3.0, this application ignores query errors by default in order to allow the results to be processed from all servers. This can be useful if you have one DNS server from the group unreachable or providing invalid results. If however you wish to restore the previous behavior you can specify either the dns-errors-fatal or def flags, or set dns_errors_fatal = true in the config.toml config file. The example below assumes that you've set dns_errors_fatal = true in the config.toml config file.

Example:

$ dnsc -config-file ./config.example.toml -q www.penzoil.com
  INFO[0000] User-specified config file provided, will attempt to load it
  INFO[0000] Trying to load config file "./config.example.toml"
  INFO[0000] Config file successfully loaded config_file=./config.example.toml


Server     RTT     Query              Type    Answers                       TTL
---        ---     ---                ---     ---                           ---
8.8.4.4    33ms    www.penzoil.com    A       65.52.64.201 (A)              899
8.8.4.4    8ms     www.penzoil.com    AAAA    no records found for query

Here the process bailed when the first AAAA request failed. This is due to the dns_errors_fatal = true config file setting noted earlier.

Use single-line summary output format

This is the previous default output format. This format reads well when the result set is small, but may be harder to read when many records are returned for a query type (e.g., large pool of front-end web servers).

$ dnsc --ds 8.8.8.8 --q "conversations.im" -sp "xmppclient" -t a --ro single-line
  INFO[0000] User-specified config file not provided
  INFO[0000] Trying to load config file "/mnt/t/github/dnsc/config.toml"
  WARN[0000] Config file "/mnt/t/github/dnsc/config.toml" not found or unable to load
  INFO[0000] Trying to load config file "/home/ubuntu/.config/dnsc/config.toml"
  WARN[0000] Config file "/home/ubuntu/.config/dnsc/config.toml" not found or unable to load
  WARN[0000] Failed to load config files, relying only on provided flag settings


Server     RTT      Query                                 Type    Answers                                                        TTL
---        ---      ---                                   ---     ---                                                            ---
8.8.8.8    8ms      _xmpp-client._tcp.conversations.im    SRV     xmpps.conversations.im. (SRV), xmpp.conversations.im. (SRV)    1545, 1545
8.8.8.8    944ms    conversations.im                      A       78.47.177.120 (A)                                              3599

Here is an example where this format does not read quite as well:

$ dnsc --ds 8.8.8.8 -q www.yahoo.com -t a -t aaaa --ro single-line
  INFO[0000] User-specified config file not provided
  INFO[0000] Trying to load config file "/mnt/t/github/dnsc/config.toml"
  WARN[0000] Config file "/mnt/t/github/dnsc/config.toml" not found or unable to load
  INFO[0000] Trying to load config file "/home/ubuntu/.config/dnsc/config.toml"
  WARN[0000] Config file "/home/ubuntu/.config/dnsc/config.toml" not found or unable to load
  WARN[0000] Failed to load config files, relying only on provided flag settings


Server     RTT    Query            Type    Answers                                                                                                                                                                   TTL
---        ---    ---              ---     ---                                                                                                                                                                       ---
8.8.8.8    8ms    www.yahoo.com    AAAA    new-fp-shed.wg1.b.yahoo.com. (CNAME), 2001:4998:44:3507::8000 (AAAA), 2001:4998:44:3507::8001 (AAAA), 2001:4998:124:1507::f001 (AAAA), 2001:4998:124:1507::f000 (AAAA)    5, 5, 5, 5, 5
8.8.8.8    7ms    www.yahoo.com    A       new-fp-shed.wg1.b.yahoo.com. (CNAME), 74.6.143.25 (A), 74.6.143.26 (A), 74.6.231.20 (A), 74.6.231.21 (A)                                                                  39, 40, 40, 40, 40

Inspiration

This project was inspired by a small script that I used for many years to quickly spot outliers with DNS servers after moving virtual servers between subnets. The shell script is usable, but crude. It is provided as-is and can be found here:

dns_query.sh

This project also owes its existence to the miekg/dns package and the Black Hat Go authors whose example code got me started. See the References section for links to both resources. Many thanks to the authors of both!

References

• Golang basics

  • https://golang.org/pkg/sort/#Slice
  • https://golang.org/pkg/flag/#example_
  • https://stackoverflow.com/questions/24886015/how-to-convert-uint32-to-string
  • https://www.geeksforgeeks.org/nested-structure-in-golang/

• TOML config file-related

  • https://github.com/toml-lang/toml#user-content-array
  • https://github.com/pelletier/go-toml

• DNS library

  • https://github.com/miekg/dns
  • https://miek.nl/2014/august/16/go-dns-package/
  • https://nostarch.com/blackhatgo
    • https://github.com/blackhat-go/bhg/blob/master/ch-5/get_all_a/main.go

• Free DNS servers for testing purposes

  • https://developers.google.com/speed/public-dns
  • https://www.opendns.com/setupguide/
  • https://blog.cloudflare.com/announcing-1111/

• Definitions

  • https://www.cloudflare.com/learning/cdn/glossary/round-trip-time-rtt/