tanji / nm-separate-dns

Generate dnsmasq config files per connection to separate dns queries

Generate dnsmasq config files per connection to separate DNS queries

Automatically configure dnsmasq to separate DNS queries based on the domain name. This is helpful if you have a local private LAN with its own DNS server, and need to connect to a VPN which serves a different private domain.

Environment where this script can be used

The following network environment benefits from this script:

• local (home) LAN with its own recursive DNS server (example.net)
• remote VPN (work) with its own non-recursive DNS (example.com)

Sending a DNS query for example.com to the example.net DNS server will not return a useful address. Neither will sending an example.net request to the example.com DNS server get anything. The configuration in /etc/resolv.conf is limited, and it is not possible to specify a dedicated DNS server for a specific domain.

dnsmasq is a caching DNS server that has a very flexible configuration. Because many workstations have dnsmasq installed already (it is a dependency for libvirt), using dnsmasq for configuring a local DNS server should (mostly) not require additional dependencies.

Note: Before using this solution, test if the integrated dnsmasq feature of NetworkManager is sufficient for your environment. NetworkManager can maintain a dnsmasq configuration and (re)start the dnsmasq daemon too. All this requires, is a configuration option in /etc/NetworkManager/NetworkManager.conf:

[main]
dns=dnsmasq

Installation

1. Copy the 90-update-resolv.conf script to /etc/NetworkManager/dispatcher.d/ and make it executable.

2. Create the /etc/dnsmasq.d/localhost.conf with the following content

   no-resolv
   no-poll
   interface=lo
   no-dhcp-interface=lo
   bind-interfaces
   

3. Install and enable dnsmasq:

   # yum install dnsmasq
   # systemctl enable dnsmasq
   # systemctl start dnsmasq
   

4. Disable updating /etc/resolv.conf by NetworkManager. In /etc/NetworkManager/NetworkManager.conf make sure to have the following option:

   [main]
   dns=none
   

   After editing the NetworkManager.conf, you will need to restart NetworkManager:

   # systemctl restart NetworkManager
   

5. (Re)Connect your LAN, WiFi and VPN.

Known working NetworkManager VPN plugins

This script is regulary tested with at least these plugins:

• NetworkManager-openvpn
• NetworkManager-openswan

Previous versions and upstream repository

The script was initially posted for RHEL-6, but it seems that NetworkManager (mainly nmcli) is a moving target and requires to some changes for this script to keep working.

The latest version of this script is available in its github repository.