DNS Hardening on Manjaro: Ignore DHCP

A rabbit hole but who is to blame?

Introduction

This article aims to show how easy it is to configure DNS on a Manjaro host so that you do not rely on the configuration the DHCP server provides. Having a proper DNS configuration is not something you do just to brag, but it comes with serious security, privacy and performance considerations.

To help you understand: by blindly following your DHCP provider’s suggestions when it comes to DNS, you risk:

  • security: If they have a misconfigured or insecure DNS server, DNS poisoning can occur at that level. You might think you’ve visited your bank’s website, but in actuality, you are just visiting a malicious clone.
  • privacy: If a provider wants to track your internet activity, it is trivial to do so: they can see all websites that you visit (without the need for extensive infrastructure - for plain MitM attacks).
  • performance: Inadequate DNS servers have the potential to slow all your requests down.

Make sure to avoid copying the exact same configuration if you (or your company) has a dedicated DNS server; otherwise, you might lose access to certain endpoints and severely impact your workflow.

Only read if you have absolutely no idea what DNS is

If you’re reading this, then in all probability your network (at least your home one) looks like this:

20260320_131349_screenshot.png
Figure 1: Gloriously sketched home network

We have a device that we are quick to call a router but in actuality, it is much more than that. It also functions as a:

  • Wireless Access Point - Providing wireless access to our devices
  • Ethernet (/ Layer 2) Switch - Providing LAN functionality
  • Network Attached Storage (NAS) - Strangely, I’ve seen a lot of people attach a hard drive directly to the router when this functionality is supported
  • and so much more, but crucially it also
  • WORKS AS A DHCP SERVER1

DHCP

This simplified model of the network focuses on IPv4. IPv6 introduced different ways of handling many of the underlying parts.

Now, what is a DHCP server you might ask… To understand that I’ll (grossly) explain in a paragraph all of computer networking (-_-): I’m sure that you’ve seen or heard many times that computers have IP addresses. If you’ve ever thought about it, I’m pretty sure that you reached the following conclusion: they can’t be born with them2 since an address must always be able to reach you, no matter where you are (which network you are connected to). And that is right! I’ll keep simplifying, but you can think of your over-the-internet communications according to the following pattern:

  1. You somehow (that’s DNS) find the IP of the server/computer you want to talk to.
  2. You create the message with that Destination IP and your address as Source IP. Not knowing where to send it, you pass it to your router.
  3. Your router does its magic and forwards it to a path that will ultimately reach Destination IP and waits for its answer (the server will send their reply to your Source IP).
  4. Your Source IP obviously needs to somehow be linked to your router (otherwise, how would the network know where to forward it to reach you?).

A lot of interesting stuff might happen when it comes to generating your IP, but let us ignore them. We’ve proven that it is necessary, and that it is related to your router in one way or another. When it comes to home networks, your IP is leased by the DHCP server inside your router: when you connect, you ask for it, and you receive one for a given time. That’s it… almost.

There are many significant technologies that are hidden in this simplistic model (such as NAT), but these are not needed in this context.

You see, DHCP servers are usually kinda nice and want to help you out. So, instead of just handing out addresses, they also give you some extra information such as those for:

  • The router
  • The DNS servers

DNS

We took a long way to get here! DNS stands for Domain Name System and it is effectively a protocol for us to go from a Name to an Address. 

 -> nslookup google.com
Server:		127.0.0.53
Address:	127.0.0.53#53

Non-authoritative answer:
Name:	google.com
Address: 192.178.24.46
Name:	google.com
Address: 2a00:1450:4017:812::200e

The default DNS stack on Manjaro

By default, Manjaro lets NetworkManager handle practically everything around networking, which includes DHCP and DNS configuration. Thus, systemd-resolved might be installed but is disabled: we trust that the DHCP server promotes the name servers we want. Have a look at /etc/resolv.conf (for you non-believers): 

# Use this to verify that systemd-resolved is in fact disabled
systemctl status systemd-resolved

# My hallucinated /etc/resolv.conf
# This often is not an actual file, but a link to somewhere else in the system.
search home.arpa
nameserver 192.168.1.1
nameserver 8.8.8.8

It works (but we’ll break it).

The Goal

The rest of this article covers how we’ll:

  • force NetworkManager to ignore DNS servers advertised by the network and instead rely on systemd-resolved
  • enable systemd-resolved
  • configure systemd-resolved (and add a couple of security features)

Before moving on, make sure that you understand what you’re doing. If in doubt, read some more.

NetworkManager let go of DNS pleeeeeeease

Simply enough, you’ll see that NetworkManager, following the standard convention, can be configured through: /etc/NetworkManager/conf.d/<files>

All we need, thus, is to edit (or create) dns.conf in that directory: 

# /etc/NetworkManager/conf.d/dns.conf
[main]
# This tells NM to avoid passing information to systemd-resolved
dns=none
systemd-resolved=false

In this process we effectively redirect the /etc/resolv.conf file to the stub created by systemd-resolved. The system then knows to look to systemd-resolved, but without proper configuration, it receives information from NetworkManager.

Configure systemd-resolved

In the same way, either through man 5 resolved.conf or by visiting /etc/systemd/resolved.conf, we’ll see that a standard configuration (minimal) is suggested: 

[Resolve]
# Some examples of DNS servers which may be used for DNS= and FallbackDNS=:
# Cloudflare: 1.1.1.1#cloudflare-dns.com 1.0.0.1#cloudflare-dns.com 2606:4700:4700::1111#cloudflare-dns.com 2606:4700:4700::1001#cloudflare-dns.com
# Google:     8.8.8.8#dns.google 8.8.4.4#dns.google 2001:4860:4860::8888#dns.google 2001:4860:4860::8844#dns.google
# Quad9:      9.9.9.9#dns.quad9.net 149.112.112.112#dns.quad9.net 2620:fe::fe#dns.quad9.net 2620:fe::9#dns.quad9.net
#
# Using DNS= configures global DNS servers and does not suppress link-specific
# configuration. Parallel requests will be sent to per-link DNS servers
# configured automatically by systemd-networkd.service(8), NetworkManager(8), or
# similar management services, or configured manually via resolvectl(1). See
# resolved.conf(5) and systemd-resolved(8) for more details.

Not only does it give us properly formatted entries to use for DNS, but it also explains neatly that if misconfigured, other services such as NetworkManager may affect our active DNS configuration.

Visiting the suggested manpage explains the syntax in each of the Cloudflare, Google and Quad9 lines: 

# From man 5 resolved.conf
    DNS=
        A space-separated list of IPv4 and IPv6 addresses to use as system DNS servers. Each address can optionally take a port number
        separated with ":", a network interface name or index separated with "%", and a Server Name Indication (SNI) separated with "#".
        When IPv6 address is specified with a port number, then the address must be in the square brackets. That is, the acceptable full
        formats are "111.222.333.444:9953%ifname#example.com" for IPv4 and "[1111:2222::3333]:9953%ifname#example.com" for IPv6. DNS
        requests are sent to one of the listed DNS servers in parallel to suitable per-link DNS servers acquired from systemd-
        networkd.service(8) or set at runtime by external applications. For compatibility reasons, if this setting is not specified, the
        DNS servers listed in /etc/resolv.conf are used instead, if that file exists and any servers are configured in it. This setting
        defaults to the empty list.

At this point, one could just copy any of these as the DNS= and a different one as the FallbackDNS= and skip over to the part where we enable systemd-resolved. However, this article will not stop at that: 

[Resolve]
DNS=1.1.1.1#cloudflare-dns.com 1.0.0.1#cloudflare-dns.com 2606:4700:4700::1111#cloudflare-dns.com 2606:4700:4700::1001#cloudflare-dns.com
FallbackDNS=9.9.9.9#dns.quad9.net 2620:fe::9#dns.quad9.net 1.1.1.1#cloudflare-dns.com 2606:4700:4700::1111#cloudflare-dns.com 8.8.8.8#dns.google 2001:4860:4860::8888#dns.google

Hardening

Why bother? Adding a couple of minutes to this configuration can make your browsing more secure and private by enabling the following features:

  • DNS over TLS: This encrypts your DNS Queries through TLS so that it is difficult for others to eavesdrop on your requests. In an ideal world, this setting would mean that only your DNS Server knows what you asked for: Privacy.
  • DNSSEC handles security by providing integrity: its mechanisms make it difficult for anyone to give false information or tamper with the responses: the response must come from the legitimate owners of that domain.

These are both easily added to one’s configuration: 

[Resolve]
DNS=1.1.1.1#cloudflare-dns.com 1.0.0.1#cloudflare-dns.com 2606:4700:4700::1111#cloudflare-dns.com 2606:4700:4700::1001#cloudflare-dns.com
FallbackDNS=9.9.9.9#dns.quad9.net 2620:fe::9#dns.quad9.net 1.1.1.1#cloudflare-dns.com 2606:4700:4700::1111#cloudflare-dns.com 8.8.8.8#dns.google 2001:4860:4860::8888#dns.google
DNSSEC=yes
DNSOverTLS=allow-downgrade
ReadEtcHosts=yes
Cache=yes

In this snippet I have DNSOverTLS=allow-downgrade, since it is notoriously easy for DoT to fail. However, if you do not mind your connection breaking down, use DNSOverTLS=yes instead.

Enabling systemd-resolved

If you’ve followed so far, all you need to do is:

  • enable the service
  • make NetworkManager reload its configuration so that it does not handle DNS
sudo systemctl enable --now systemd-resolved
sudo systemctl restart NetworkManager

Verifying the installation

This article would not be complete if it did not include the following tests to verify that we did in fact configure the system properly: 

# These tests are within resolvectl
resolvectl status # look for DNSOverTLS, DNSSEC

resolvectl statistics

You can also verify DNSSEC against this domain (it should fail): 

resolvectl query sigfail.verteiltesysteme.net

Finally, you can have a look at NetworkManager DNS-related settings using: 

nmcli connection show $yourconnection | grep dns

A couple of notes on resolvectl status

  • If you see that resolv.conf mode: foreign, it usually means that somehow that file is not a link to the usual systemd-resolved stub. You might want to use:
    • sudo ln -sf /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
    • Fixing that will show resolv.conf mode: stub

  • If you see proper Global options, but your interface is still using the DHCP provided configuration: According to this, the NetworkManager configuration should suffice. For me, it required restarting: after restarting, this resulted in me seeing an empty configuration for my interface, thus falling back on my Global options. 

    Link 2 (enp2s0)
    Current Scopes: LLMNR/IPv4 LLMNR/IPv6 mDNS/IPv4 mDNS/IPv6
        Protocols: -DefaultRoute +LLMNR +mDNS +DNSOverTLS
                    DNSSEC=yes/supported
    Default Route: no

You might see too many breadcrumbs in ArchWiki and in multiple random posts, pointing to the modification of /etc/systemd/networkd.conf (or sub-configuration files) to have UseDNS=false. Just make sure that systemd-networkd is enabled first (not by default) because otherwise, all actions will be futile.

Resources / Further reading:

Footnotes:

1

Could even work as a DNS server, but I’m willing to let that go :P

2

Although, crucially, MAC addresses pretty much work that way, but still an oversimplification.

Originally created on 2026-03-20 Fri 12:39

Made with Emacs and Org.
© 2026 Lamprinos Chatziioannou. Content may be shared with attribution.