Skip to main content

Migrating from iptables to nftables

nftables has been enabled by default in latest Ubuntu and Debian, but not fully supported by Docker.

I've been hestitating about migrating from iptables to nftables, but managed to do it today.

Here are my thoughts.

Scripting nftables

The syntax of iptables and nftables are different, but not that different, both are more or less human readable. However, nftables is clearly more friendly for scripting.

I spent quite some time in a python script to generate a iptables rule set, and I was worried that I need lots of time migrating the script. Aftering studying the syntax of nftables, I realized that I could just write /etc/nftables.conf directly. 

In the conf file I can manage tables and chains in a structured way. I'm free to use indentations and new lines, and I no longer need to write "-I CHAIN" for every rule.

Besides, I can group similar rules (e.g. same rule for different tcp ports) easily, and I can define variables and reuse them. 

Eventually I was able to write a nice nftables rule set quickly with basic scripting syntax. It was not as powerful as my custom python script, but it is definitely easier to write. Further, I think it might be worth learning mapping in the future.

Tables & Chains in nftables

Unlike iptables, nftables is decentralized. Instead of pre-defined tables (e.g. filter) and chains (e.g. INPUT), nftables uses hooks and priorities. It sounds like event listeners in JavaScript.

One big difference is: a packet is dropped if it is dropped any matching rule, and a packet is accepted only if all relevant chains accept the packet. Again, this is similar to event listeners. On the other hand, in iptables, a packet is accepted if it is accepted by any rule. It sounds a bit confusing at the beginning, but I think nftables is more flexible, especially in my cases, see below.

Docker & nftables

Docker does not support nftables, but it add rules via iptables-nft. It was painful to managed iptables rules with Docker:
  • Docker creates its own DOCKER and DOCKER-USER chains, which may accept some rules.
  • If I need to control the traffic from/to containers, I need to make sure that the rules are defined before or in DOCKER-USER.
  • Docker may or may not be started at boot. And Docker adds DOCKER to INPUT, so I need to make sure that my rules are in effect in all cases.
Well all the mess is because: in iptables, a packet is accepted if it is accepted by any rule. That means I must insert my REJECT rules before DOCKER/DOCKER-UESR, which might accept the packet.

This is no longer an issue in nftables! I can simply define my own tables and reject some packets as I like.

Finally, I don't need to touch the tables created by Docker via iptables-nft, instead I can create my own nft tables.

Conclusions

I had lots of worries about nftables, about scripting and working with Docker. As it turned out, none was actually an issue thanks to the new design of nftables!

Comments

Popular posts from this blog

Determine Perspective Lines With Off-page Vanishing Point

In perspective drawing, a vanishing point represents a group of parallel lines, in other words, a direction. For any point on the paper, if we want a line towards the same direction (in the 3d space), we simply draw a line through it and the vanishing point. But sometimes the vanishing point is too far away, such that it is outside the paper/canvas. In this example, we have a point P and two perspective lines L1 and L2. The vanishing point VP is naturally the intersection of L1 and L2. The task is to draw a line through P and VP, without having VP on the paper. I am aware of a few traditional solutions: 1. Use extra pieces of paper such that we can extend L1 and L2 until we see VP. 2. Draw everything in a smaller scale, such that we can see both P and VP on the paper. Draw the line and scale everything back. 3. Draw a perspective grid using the Brewer Method. #1 and #2 might be quite practical. #3 may not guarantee a solution, unless we can measure distances/p...

Installing Linux on Surface Pro 1g

Windows 10 will soon reach its end of life, and my 1-gen Surface Pro is not supported by Windows 11. I (finally) decided to install Linux to it. Fortunately, it's a not-so-easy nice adventure: The device has only one USB port, so I have to bring back my 10+-year old USB hub. My live USB drive cannot boot directly, I have to disable Secure Boot first, by holding Volume Up during boot. I think years ago I learned that booting on USB might not work through a USB hub, but fortunatelly it worked well with my setup. This is done by holding Volume Down during boot. Wifi adapter was detected in the live Linux environment, but not functional. And I don't have a USB-Ethernet adapter. Luckily, nowadays we have USB-tethering from Android phones, which works out-of-the-box. Originally I planned to following this guide to set up root on ZFS, however, the system froze when building the ZFS kernel module. Then I decided to just use EXT4, yet I still learned a lot from the guide about disk par...

Fix Google Security Code

Google Security Code (http://g.co/sc) is one type of 2-step verification. This is particularly useful when security keys and passkeys are not available. I have been using it in my LXC containers, until today I found out that it stopped working. It just kept saying "The code is invalid". It is easy to rule out some factors: The code works on other browsers on my laptop. The code works on other devices that are directly connected to the router. So it appears that Google also checks IP addresses besides the security code. Recently I have IPv6 enabled, so most devices that are directly connected to the router have both IPv4 and IPv6 addresses. But  I only enabled IPv4 for my LXC containers. So I guess when a code is generated by device A and used by device B, Google should be able to check that device A and device B are closely located. But in my case, IPv6 address appears on device A but not on device B, which may look suspicious. To fix the problem, I just needed to disable IPv...