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Maintain local domains for your private network

#linux #vpn #dns #devops
Maintain local domains for your private network
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I have always wanted to access private servers (accessed only through VPN or SSH tunnels) through domains without going through the hassle of locally modifying hosts files in the client side (me and my colleagues) or the SSH config files, so here's my attempt to solve this problem.

I used a t3a.nano AWS EC2 instance to demonstrate the idea with Ubuntu 20.04 on it, with OpenVPN as my VPN server and dnsmasq as a DNS server.

I used dnsmasq instead of something like BIND because it's much easier to setup and maintain.

OpenVPN

This was made only for demonstration purpose, so to quickly setting up an OpenVPN server without pain I used angristan/openvpn-install script to do so.

curl -O https://raw.githubusercontent.com/angristan/openvpn-install/master/openvpn-install.sh

chmod +x openvpn-install.sh

CLIENT=<name of your choice> PORT_CHOICE=2 PORT=443 PROTOCOL_CHOICE=2 AUTO_INSTALL=y ./openvpn-install.sh
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This will generate an OpenVPN profile with the name you chose in your home directory.

systemd-resolvd

In order for the DNS server we will use we have to disable systemd-resolvd from listening to port 53:

# /etc/systemd/resolved.conf

[Resolve]
DNSStubListener=no
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dnsmasq 

apt install dnsmasq
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Set localhost addresses as the only nameservers in /etc/resolv.conf to route all the DNS queries to our DNS server

# /etc/resolv.conf

nameserver ::1
nameserver 127.0.0.1
options trust-ad
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Now for the dnsmasq configuration:

# /etc/dnsmasq.conf

no-resolv
local=/lan/
listen-address=::1,127.0.0.1,10.0.1.136
expand-hosts
domain=lan
cache-size=1000
server=8.8.8.8
server=8.8.4.4
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dnsmasq configuration explained:

no-resolv: don't read /etc/resolv.conf

listen-address: The addresses we want to listen for a connection from. 10.0.1.136 is the private IP of the EC2 instance dnsmasq is installed in.

domain and local: our custom domain .lan

expand-hosts: To read hostnames from /etc/hosts and resolve it as hostname.lan

cache-size: cache 1000 DNS query. Default is 150.

server: if dnsmasq can't resolve the query call an external server

To add a new host or domain to the network simply add it in the hosts file:

# /etc/hosts

...
10.0.1.136 messi
10.0.1.136 salah
...
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Test our setup

Now to test if our configuration works I run dig from my client machine, which is connected to my private network through VPN, with the domains messi.lan and salah.lan

messi.lan

# dig messi.lan
; <<>> DiG 9.16.8-Ubuntu <<>> messi.lan
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 56241
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;messi.lan.         IN  A

;; ANSWER SECTION:
messi.lan.      0   IN  A   10.0.1.136

;; Query time: 448 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; MSG SIZE  rcvd: 54
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salah.lan

# dig salah.lan
; <<>> DiG 9.16.8-Ubuntu <<>> salah.lan
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 43569
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 65494
;; QUESTION SECTION:
;salah.lan.         IN  A

;; ANSWER SECTION:
salah.lan.      0   IN  A   10.0.1.136
;; Query time: 384 msec
;; SERVER: 127.0.0.53#53(127.0.0.53)
;; MSG SIZE  rcvd: 54
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Both returned our server IP address in the answer section. It works perfectly.

You can even use any web server (e.g: nginx) to test out setup by specifying different server names and request it from our client machine.

Notes

  • You might need to configure your OpenVPN client to use your DNS server address.

Alt Text

To Do

  • Configure OpenVPN to route only internal traffic through the VPN
  • Cache the DNS queries locally to improve performance.
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