Submit query against a list of DNS servers and display summary of results
- Project home
- Overview
- Features
- Changelog
- Requirements
- Installation
- Configuration
- 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
See our GitHub repo for the latest code, to file an issue or submit improvements for review and potential inclusion into the project.
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.
-
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
See our GitHub repo for planned future work.
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.
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.
- Go
- see this project's
go.modfile 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")
- see this project's
- GCC
- if building with custom options (as the provided
Makefiledoes)
- if building with custom options (as the provided
make- if using the provided
Makefile
- if using the provided
- Windows 10
- Ubuntu Linux 18.04+
- Red Hat Enterprise Linux 7+
- Download Go
- Install Go
- Clone the repo
cd /tmpgit clone https://github.com/atc0005/dnsccd dnsc
- Install dependencies (optional)
- for Ubuntu Linux
sudo apt-get install make gcc
- for CentOS Linux
sudo yum install make gcc
- for Ubuntu Linux
- Build
- for current operating system
go build -mod=vendor ./cmd/dnsc/- forces build to use bundled dependencies in top-level
vendorfolder
- forces build to use bundled dependencies in top-level
- for all supported platforms (where
makeis installed)make all
- for Windows
make windows
- for Linux
make linux
- for current operating system
- 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/
- if using
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).
- Download the latest release binaries
- Decompress binaries
- e.g.,
xz -d dnsc-linux-amd64.xz
- e.g.,
- Deploy
- Place
dnscin a location of your choice- e.g.,
/usr/local/bin/
- e.g.,
- Place
NOTE:
DEB and RPM packages are provided as an alternative to manually deploying binaries.
The priority order is:
- Command line flags (highest priority)
- Configuration file
- 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.
These are the record types currently supported:
CNAMEAAAAAMXNSPTRSRV
Other types will be added as I encounter a need for them, or as requested.
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 |
- Flags marked as
requiredmust 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 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(ordnsc.exe) binary (asconfig.toml) - at
$HOME/.config/dnsc/config.tomlon a UNIX-like system (e.g., Linux distro, Mac) - at
C:\Users\YOUR_USERNAME\AppData\dnsc\config.tomlon 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.
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.
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 22Since 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.
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. 52You 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 44No errors here since www.yahoo.com had records for all of the requested
query types.
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: 2022-06-01T06:30:32-05:00Not 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 186In 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 2533In 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 2837As 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 3599As 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 queryHere the process bailed when the first AAAA request failed. This is due to
the dns_errors_fatal = true config file setting noted earlier.
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) 3599Here 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, 40This 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:
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!
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Golang basics
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TOML config file-related
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DNS library
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Free DNS servers for testing purposes
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Definitions