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!

Labels:

Comments

Post a Comment

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...
2 comments
Read More »

[转] UTF-8 and Unicode FAQ for Unix/Linux

这几天,这个东西把我搞得很头疼 而且这篇文章好像太大了,blogger自己的发布系统不能发 只好用mail了 //原文 http://www.cl.cam.ac.uk/~mgk25/unicode.html UTF-8 and Unicode FAQ for Unix/Linux by Markus Kuhn This text is a very comprehensive one-stop information resource on how you can use Unicode/UTF-8 on POSIX systems (Linux, Unix). You will find here both introductory information for every user, as well as detailed references for the experienced developer. Unicode has started to replace ASCII, ISO 8859 and EUC at all levels. It enables users to handle not only practically any script and language used on this planet, it also supports a comprehensive set of mathematical and technical symbols to simplify scientific information exchange. With the UTF-8 encoding, Unicode can be used in a convenient and backwards compatible way in environments that were designed entirely around ASCII, like Unix. UTF-8 is the way in which Unicode is used under Unix, Linux, and similar systems. It is now time to make sure that you are well familiar ...
Post a Comment
Read More »

Moving Items Along Bezier Curves with CSS Animation (Part 2: Time Warp)

This is a follow-up of my earlier article.  I realized that there is another way of achieving the same effect. This article has lots of nice examples and explanations, the basic idea is to make very simple @keyframe rules, usually just a linear movement, then use timing function to distort the time, such that the motion path becomes the desired curve. I'd like to call it the "time warp" hack. Demo See the Pen Interactive cubic Bezier curve + CSS animation by Lu Wang ( @coolwanglu ) on CodePen . How does it work? Recall that a cubic Bezier curve is defined by this formula : \[B(t) = (1-t)^3P_0+3(1-t)^2tP_1+3(1-t)t^2P_2+t^3P_3,\ 0 \le t \le 1.\] In the 2D case, \(B(t)\) has two coordinates, \(x(t)\) and \(y(t)\). Define \(x_i\) to the be x coordinate of \(P_i\), then we have: \[x(t) = (1-t)^3x_0+3(1-t)^2tx_1+3(1-t)t^2x_2+t^3x_3,\ 0 \le t \le 1.\] So, for our animated element, we want to make sure that the x coordiante (i.e. the "left" CSS property) is \(...
3 comments
Read More »