aether

aether

the clear sky; the upper regions of air beyond the clouds

Table of Contents

• aether
  • Quickstart
  • How It Works
  • Config
  • Example usage
  • Libraries that made this project possible

aether is a DNS server written in golang. It has support for adding your own domain resolvers, as well as serving custom zonefiles, e.g. with for a TLD of .example.

• aether has a small footprint, can be served on any port as well as specifying any DNS resolver in case it doesn't have the record cached.
• aether has a dockerfile in case you would like to try it out, the image size is around 8MB.
• Use cases for this would be to forward DNS traffic if you're behind a VPN so they don't leak.
• Hiding some services by using the aether to serve the domains you need instead of publishing them at your domain registar you can secure specific services.
• Since you can supply your own zonefiles you can create an adblock service simply by feeding the data to the server.
• Almost everything is logged to the standard output (everything except the DNS queries themselves) as that would expand the log size by quite a large amount.

Quickstart

If you want to skip ahead and test what this can do you can either build the app:

git clone https://gitlab.com/shagon/aether.git && cd aether
go get -v && go build

Additionally docker containers are also provided. You can find them here or just run it as:

$ docker run -it --rm -p 53:53/udp registry.gitlab.com/shagon/aether:master

How It Works

1. All DNS records are served from the application cache, if you enter a custom zonefile those will have presedence over forwarding the query to another DNS server (supplied as -forward-server).
2. If zonefiles are supplied aether checks for the etag response header in case the record updates so it can renew the data. If there is no etag header currently the cache key will be empty however most webservers already send this header.
3. If started as a service the logging is useful in case you have any errors as well as to manage the server.
4. By default if started without any parameters it will act as a DNS forwarder.

Config

aether supports multiple command line arguments.

• -forward-server: the DNS server that aether will contact in case the result is not located in its cache (default "1.1.1.1:53"), note: if supplying the forward-server include the port, e.g. 8.8.8.8:53
• -interface: the interface to listen to (default "0.0.0.0")
• -port: the port to use (default "53"), if running on linux anything below 1024 are restricted and as such require root permissions; you can serve the DNS on non standard ports with this, e.g. on port 5300
• -refresh: default refresh time for the zonefiles, the zonefiles themselves are specified with the -zone parameter (default 60 seconds), to specify a higher or lower TTL for the files provided simply enter the time in seconds, example: -refresh 5 would check for changes every 5 seconds; an example of specifying an hour would be to pass the whole number as -refresh 3600 or rely on arithmetics, e.g. in bash: -refresh $((60*60)) is the same as -refresh 3600
• -zone value RFC1035 (bind9 format) zonefiles to use, an example zonefile would either be complete:

; example.demo domain name
$TTL 3600
$ORIGIN example.demo.

@    IN A 1.2.3.4
ns   IN A 1.1.1.1
mail IN A 4.3.2.1

@     IN MX 20 cname.example.demo.
@     IN NS ns
@     IN TXT "example txt record"
@     IN SOA ns support 1 10800 3600 604800 3600
cname IN CNAME example.demo.

This would return the following when checked:

$ dig +noall +answer A example.demo @localhost
example.demo.		3600	IN	A	1.2.3.4

$ dig +noall +answer A ns.example.demo @localhost
ns.example.demo.	3600	IN	A	1.1.1.1

$ dig +noall +answer A mail.example.demo @localhost
mail.example.demo.	3600	IN	A	4.3.2.1

$ dig +noall +answer MX example.demo @localhost
example.demo.		3600	IN	MX	20 cname.example.demo.

$ dig +noall +answer NS example.demo @localhost
example.demo.		3600	IN	NS	ns.example.demo.

$ dig +noall +answer TXT example.demo @localhost
example.demo.		3600	IN	TXT	"example txt record"

$ dig +noall +answer SOA example.demo @localhost
example.demo.		3600	IN	SOA	ns.example.demo. support.example.demo. 1 10800 3600 604800 3600

$ dig +noall +answer CNAME cname.example.demo @localhost
cname.example.demo.	3600	IN	CNAME	example.demo.

However you can also supply the zones as:

$TTL 3600
example.com.        IN A 1.2.3.4
random.domain.name. IN A 2.2.2.2

Please note the dot at the end of the record, example.com., since we did not specify an $ORIGIN we need to add the trailing dot at the end.

This would return the following:

$ dig +noall +answer example.com @localhost
example.com.  3600	IN	A	1.2.3.4

$ dig +noall +answer random.domain.name @localhost
random.domain.name.  3600	IN	A	2.2.2.2

Example usage

• Start the program with one specific zonefile

aether -zone https://domain.com/file.zone

• Start the program with multiple zonefiles

aether -zone https://domain.com/file.zone -zone https://example.com/zonefile

• Set the TTL / refresh time of the zonefiles to 2 hours

aether -refresh 7200 -zone https://domain.com/zonefile 

• Change the default port and interface

aether -interface 127.0.0.1 -port 5678

• Change the defaults

aether -interface 127.0.0.1 -port 5353 -refresh 3600 -forward-server 8.8.8.8:53 -zone https://domain.com/zonefile

Libraries that made this project possible

• go.uber.org/zap - logger
• github.com/miekg/dns - main dns library

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