The first thing everyone should do before connecting to the Internet is to set up a proper firewall. Since Debian 10 (Buster), the iptables framework is replaced by the nftables framework.

To make it easier to get started, here is a short guide on how to get your firewall up and running in no time.

Step 1: install some tooling

I mentioned that Debian uses the nftable framework by default, but it is not enabled!

To enable the default firewall, you have to do the following:

$ sudo apt install nftables

# You should start nftables at system start, so you should enable it.
$ sudo systemctl enable nftables.service

Step 2: Configuration

So, we have a firewall, we’re done!

The default configuration file is in /etc/nftables.conf, so we dive into the configuration.

Here is a basic configuration file for a web server with everything you need to get started.

#!/usr/sbin/nft -f

flush ruleset

table inet filter {
  chain input {
    type filter hook input priority 0;

      # accept any localhost traffic
      iif lo accept

      # accept trafic originated from us
      ct state established,related accept

      # drop invalid packets
      ct state invalid counter drop

      # accept http, https
      tcp dport { 80,443 } accept

      # ssh for ip range
      ip saddr tcp dport 22 accept
      ip saddr tcp dport 22 accept
      tcp dport 22 drop

      # mosh for ip range
      ip saddr udp dport 60000-60005 accept
      ip saddr udp dport 60000-60005 accept
      udp dport 60000-60005 drop

      # accept icmp
      ip protocol icmp accept

      # accept icmpv6
      ip6 nexthdr icmpv6 accept

      #  meta nfproto ipv6
      icmpv6 type { nd-neighbor-advert, nd-neighbor-solicit, nd-router-advert} ip6 hoplimit 1 accept
      icmpv6 type { nd-neighbor-advert, nd-neighbor-solicit, nd-router-advert} ip6 hoplimit 255 counter accept

      # count and reject everithing else
      counter reject with icmpx type admin-prohibited

  chain forward {
    type filter hook forward priority 0;
  chain output {
    type filter hook output priority 0;

The configuration should be relatively self-explanatory. I prefer to configure an IP range that is allowed to connect via ssh (mosh). If you have a dynamic IP, you have to find another solution to reduce the attack surface on your server.

Step 3: Starting the firewall

If you check the status of your firewall with sudo service nftables status, you will see that it is not yet running.
So let’s reload the configuration by running sudo nft -f /etc/nftables.conf and check if the configuration is correctly loaded by running sudo nft list table inet filter -n -a.

If there are no errors, we start the firewall by running sudo service nftables start!

If you want to secure your ssh connection even more you can continue with Securing ssh connections with ed25519 keys