Let's assume:

• I have little or no knowledge of the inner workings of the Ubuntu/Linux OS. All I know is from my experience of Windows, is that I have to have a firewall configured and running before I connect to the Internet, otherwise my system would be about as secure as going on holiday and leaving my house with all the doors and windows open.


• I have just migrated to Ubuntu desktop 18.04 LTS and have just logged in for the first time. I want to secure my system before I connect my pc to the Internet.

(NB: Note the emphasis on the word desktop, so any references to server will not be pertinent to the question and therefore irrelevant)

and after some research on this subject I understand this much:

a. Is ufw the default firewall "configuration tool" for Ubuntu? (note it says configuration tool and not the actual firewall) and ufw is installed, but it is not running and is not configured at all, so it has no default rules set out of the box.

b. Gufw is a UI to ufw, but it's not installed by default, or at least that is the case with Ubuntu Desktop 18.04 LTS.

c. iptables is the actual firewall which is built-in to the kernel as a module.

At this point know I can configure ufw as it's easy as abc, hence its name and to use it, as a starting point, you need to set deny (incoming), allow (outgoing) and start it, I also understand I could use Gufw to do this too. So I could just leave it there and do just that.

However, after all my research, I find many articles, questions and blogs on the subject with many views and opinions, many of them stating that you dont need a firewall, there are no open ports, but I am thinking, surely some ports must open when I connect to the internet? which means I am connecting my device to a network and opening up a two way traffic connection, but all the information I have read only serves to make this unclear and ambigous, so I digest all that information and try to make sense of it then reduce it down to a single statement and so a nutshell I summise:

Ubuntu desktop users don't need ufw since it's merely a configuration tool for iptables which is the actual firewall under the hood.

So say I take the above statement literally, then is the following statement true?:

iptables is the built in firewall for Ubuntu Desktop and is fully configured and up and running out of the box with default rules that are sufficiently secure for the average desktop user.

Because if the above is true, then what would be the point in ufw except to provide an uncomplicated interface to iptables, which by all accounts is complicated and furthermore the experts advise you to avoid configuring iptables directly since if you don't know exactly what you are doing, you could easily render your system insecure or unusable, if it is misconfigured?

Here is an nmap scan of my system along with my firewall config, showing the open ports on my system:

Please could someone provide a concise, relevant and non-opinion, fact based answer :)

The question changed considerably

New Answer

The TITLE Question

As a new Ubuntu desktop 18.04 LTS user, do I need to use ufw for a
firewall or is iptables sufficient?

Most home Ubuntu users don't need to or use ufw. Both ufw and iptables are installed by default and are configured to do nothing. Why there is no need, is explained in more detail below.

The Other Question 1:

So say I take the above statement literally, then is the following
statement true?:

iptables is the built in firewall for Ubuntu Desktop and is fully
configured and up and running out of the box with default rules that
are sufficiently secure for the average desktop user namely deny
(incoming), allow (outgoing).

The statement is false

The statement is actually two statements joined by and. So if just one part of the whole statement is false, then the whole statement is false. Let's break it down:

iptables is the built in firewall for Ubuntu Desktop

The above part is true.

Now let's look at the other part:

iptables is fully
configured and up and running out of the box with default rules that
are sufficiently secure for the average desktop user namely deny
(incoming), allow (outgoing).

The above part is false.

Default Ubuntu desktop installation has no ports open, and no servers running. Therefore, even though iptables come installed by default in desktop Ubuntu it is not configured to do anything. That is, the default firewall has not rules set.

Thus, iptable is configured to do nothing when you install Ubuntu.

The Other Question 2:

Explanations for nmap and gufw image (I think this is what you want)

Your nmap shows the only two open ports are open to 127.0.0.1. This is a special IP address that refers to the computer itself. That is, the computer itself can talk to itself using these two open ports.

The gufw screenshot shows that there is no firewall rules setup. However, since you installed gufw and clicked on it, ufw is also installed (gufw uses ufw) and ufw is active. The default ufw configuration you mentioned above, deny (incoming) and allow (outgoing) is working. However, these rules don't apply to the computer itself, that is 127.0.0.1. This is (not necessary but) sufficient for a home user.

Original Answer ==>

Average home users don't need a firewall

Default Ubuntu desktop installation has no ports open, and no servers running. Therefore if you don't run any server daemon, such as ssh server, you don't need any firewall. Thus, iptable is configured to do nothing when you install Ubuntu. See Do I need to activate the firewall? I only use Ubuntu for a home desktop use? for details.

If you run servers you need a firewall

If you are not an average home user, and want to do some advanced things, such as remotely access your desktop by ssh or run some other services, then you need a firewall. Your configuration of the firewall will depend on which server daemons you plan to run.

Even if you don't plan to run a server you may want a firewall with the default configuration of deny all incoming connections from all ports. This is to be doubly safe, in case, one day you want to install and run a server without realizing what you are doing. Without changing the default firewall configuration the server won't work as expected. You will scratch your head for hours before remembering that you activated the firewall. Then you may want to uninstall the server software, as it may not be worth the risk. Or you may want to configure the firewall to let the server work.

gufw is the easiest

gufw is a GUI interface for ufw, which in turn configures the iptables. Since you have been using Linux since 1990s, you may be comfortable with the command line or you may prefer the visual cues of a GUI. If you like a GUI, then use gufw. It is easy to understand and configure even for a novice.

ufw is easy

If you like the command line, ufw is easy enough.

iptables is not so easy

The reason we don't want anyone to fiddle directly with the iptables, and use ufw or gufw is because, it is very easy to mess up iptables and once you do, the system can break so badly that it may be unusable. The iptables-apply command has some built-in safeguards to protect the users from their mistakes.

Hope this helps

iptables is part of the TCP/IP networking stack. If you have *Nix you have IPTABLES. If you are on a IP network, firewall enabled or disabled, you are using iptables, regardless.

ufw is a *Nix application on top of (meaning using iptables). It is shell console based but is not so difficult to use. It can be turned on/off. You can't disable iptables as there have to be default routes for the Internet (0.0.0.0), local loopback (127.0.0.0), localhost (192.168.0.0) and auto-addressing (169.254.0.0). As you can see, iptables is baked into the networking stack. You can't avoid it even if you wanted to.

ufw can modify iptables entries in the matrix from the comfort of the shell console. It is possible to edit the iptables IP routes by hand but I won't recommend it as that is error-prone at best. Think of ufw as the tool for editing the IP route tables.

Comfortable as I may be with the shell console, I still recommend the simplicity of gufw which is the graphical "wrapper" for ufw which sits atop iptables.

I love its simplicity especially adding applications' firewall profiles such as media servers or bittorrent apps. Whatever makes my life easier earns my kudos.

So to answer your modified question, IPTABLES will not protect your network if left alone by itself. It is not designed to block, filter, disable or allow certain ports that traverses the IP route tables. Use ufw + gufw if you want to only allow/block certain ports or range of ports which in turn dynamically edit the ip route table.

I am providing this answer myself, since I was not convinced by people who are insisting you dont need a firewall, you have no open ports...
and I wont mark it accepted although I accept it myself, I'll leave it to the community to vote on whether this should be the answer.

All I would say to anyone using Ubuntu Desktop who comes across this question, if you are not sure about a firewall, because like me, you have seen for yourself are so many conflicting views on this subject, then my advice is just go ahead and use a firewall, I recommend ufw and if you want a UI then use Gufw, because when all is said and done, even if all it does is give you piece of mind, you can do no harm in using it.

I eventually turned to the official Ubuntu documentation for clarification and found the following article and after my experience trying to find answers, I would recommend you read this article because it makes a lot of sense and it answers my question and sub questions and I think I am going to be OK now ;)

https://help.ubuntu.com/community/DoINeedAFirewall

Here is an exerpt from the above article:

I have no open ports, so I don't need a firewall, right?

Well, not really. This is a common misconception. First, let us understand what an open port actually is. An open port is a port that has a service (like SSH) bound and listening to it. When the SSH client tries to communicate with the SSH server it will send a TCP SYN packet to the SSH port (22 by default), and the server will ACKnowledge it, thus creating a new connection. The misconception in how a firewall can help you begins here. Some users assume that since you are running no services, a connection can not be made. So you do not need a firewall. If these were the only things you needed to think about, this would be perfectly acceptable. However, this is only part of the picture. There are two additional factors that come into play there. One, if you do not utilize a firewall on the basis that you have no open ports, you are crippling your own security because if an application that you do have is exploited and code execution occurs a new socket can be created and bound to an arbitrary port. The other important factor here is that if you are not utilizing a firewall you also have no outbound traffic control whatsoever. In the wake of an exploited application, instead of a new socket being created and a port being bound, another alternative an attacker can utilize is to create a reverse connection back to a malicious machine. Without any firewall rules in place this connection will go through unhindered.