Installing nftables on Debian 7.5

[Last Update: 8/11/2014 – Clean up some bits around the options to select.]

This article discusses installation of nftables, the new Linux firewall software, on a Debian 7.5 system.  Nftables is under very active development and therefore the installation steps may change by the time you view this article.  Specifically, the various prerequisites needed in order to build nftables will likely no longer be needed as the software matures, and more importantly, as packages for it become available.

Note: This article begins with a base of Debian 7.5.0 netinst with the SSH Server and Standard System Utilities installed.

There are two primary components involved in an nftables system:  The first component is the Linux kernel, which provides the underlying nftables core modules.  The second component is the administration program called nft.

Compiling a kernel

The Linux kernel that comes with Debian 7.5.0 is based on version

Before you can compile a kernel, you need to get a kernel.  As of this writing, the latest stable kernel is 3.15.  Retrieving that from the Linux server with the wget command looks like this:

wget https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.15.tar.xz

Then unpack the kernel source:

tar -xvf linux-3.15.tar.xz

You’ll now have a pristine kernel ready to be built.

Several packages are essential and some are helpful for compiling a kernel on Debian.  The package named kernel-package provides useful utilities for creating a Debian packaged kernel.  Kernel-package has several prerequisites but those are all installed when you select kernel-package for installation on the system.

The method shown in this article uses the ‘menuconfig’ option to build the kernel.  Other methods such as simply the text-based config option are also available.  The menuconfig option requires the ncurses-devel package.  On Debian, this is found as part of the libncurses5-dev package and can be installed with this command (run as root):

apt-get install libncurses5-dev kernel-package

Note:  You may need to update the package list by running apt-get update prior to the packages becoming available for installation.

From within the linux-3.15 (or whatever version) directory, run:

make menuconfig

The options necessary within the kernel for nftables are found in the Networking support hierarchy.

Drill-down to the Networking support -> Networking options -> Network packet filtering framework (Netfilter).

Inside of the IP: Netfilter Configuration select IPv4 NAT.  Back up at the Network packet filtering framework menu, select IPv6 Netfilter Configuration and enable IPv6 NAT along with its sub-options of MASQUERADE target support and NPT target support.

Back at the Network packet filtering framework level, enter the Core Netfilter Configuration menu and enable Netfilter nf_tables support.  Doing so opens up several additional options.

Netfilter nf_tables mixed IPv4/IPv6 tables support
Netfilter nf_tables IPv6 exthdr module
Netfilter nf_tables meta module
Netfilter nf_tables conntrack module
Netfilter nf_tables rbtree set module
Netfilter nf_tables hash set module
Netfilter nf_tables counter module
Netfilter nf_tables log module
Netfilter nf_tables limit module
Netfilter nf_tables nat module
Netfilter nf_tables queue module
Netfilter nf_tables reject support
Netfilter x_tables over nf_tables module

Back in the Network packet filtering framework (Netfilter) level, select IP: Netfilter Configuration and find the IPv4 nf_tables support section and enable IPv4 nf_tables route chain support, IPv4 nf_tables nat chain support, and ARP nf_tables support.  Back at the Network packet filtering framework (Netfilter) level, select IPv6: Netfilter Configuration again and enable IPv6 nf_tables route chain support, and IPv6 nf_tables nat chain support.

Note: For the purposes of this article, all of the options will be selected as modules.

Finally, within the Network packet filtering framework (Netfilter) section, enable the Ethernet Bridge nf_tables support feature if you need this functionality.

Once your kernel configuration is complete, you can clean the source tree with the command:

 make-kpkg clean

Now it’s time to compile the kernel.  Depending on the speed of your system it make take several minutes to several hours.  If you have multiple processors, you can likely speed up the process by having make-kpkg use them.  This is accomplished by setting the CONCURRENCY_LEVEL environment variable.  For instance, on a system with two processors, the variable is set as such:

export CONCURRENCY_LEVEL=2
export INSTALL_MOD_STRIP=1

Alternately, specify all of it on the command line:

CONCURRENCY_LEVEL=2 INSTALL_MOD_STRIP=1 make-kpkg --initrd --revision=1 kernel_image

Note: On a dual processor quad core system the compile took about 30 minutes.

Once the kernel has been compiled, installation is accomplished (as root) with the command:

 dpkg -i linux-image-<your_version_here>.deb

Rebooting the server brings up the shiny new kernel but the server isn’t quite ready to run nf_tables yet.  Prior to compiling the nft administration program, you can verify that the nf_tables module can load.  First, see if the module is already loaded:

 lsmod | grep nf_tables

If there’s output then the module has already been loaded.  If not, then you can load the module with modprobe, as such:

 modprobe nf_tables

Rerunning the lsmod command (lsmod | grep nf_tables) should give output now, similar to this:

 nf_tables              37955  0
nfnetlink              12989  1 nf_tables

 Compiling the nft Administration Program

The nft administration program enables control over the firewall, in much the same way that the iptables command controlled an iptables-based firewall.  The nft program depends on the libmnl and libnftnl libraries.  With the large amount of active development underway on nf_tables and related libraries, this tutorial shows how to get the latest copy using Git rather than attempting to install from a package or another method.

 apt-get install autoconf2.13 libtool pkg-config flex bison libgmp-dev libreadline6-dev dblatex

Note that dblatex is only needed if you want PDF documentation, which I sometimes do.  You can save some space and security footprint by not adding dblatex to the previous apt-get command line.

The three repositories can be cloned into your current directory with the commands:

git clone git://git.netfilter.org/libmnl
git clone git://git.netfilter.org/libnftnl
git clone git://git.netfilter.org/nftables

Once a copy has been downloaded, the next step is to compile the software.  Both libnml and libnftnl are prerequisites for compiling nftables so those will be compiled first with the commands (all run as superuser/root):

 cd libmnl
./autogen.sh
./configure
make
make install

Now cd backwards a directory and into the libnftnl directory and compile it:

 cd ../libnftnl
./autogen.sh
./configure
make
make install

Finally, compile nftables:

 cd ../nftables
./autogen.sh
./configure
make
make install

With the nftables administration program compiled and installed you can now run nft commands!  Depending on your installation, you may need to reboot and/or run ldconfig.  I did both; a reboot didn’t fix it so running ldconfig as root was the next logical step.  Actually, that might have been the first logical step before rebooting, but that’s how it goes sometimes.

In any event, running the following command should do nothing (and that’s what we want right now):

 nft list tables

If the command returns nothing at all, then nft is working fine.  You can create a table with the command:

 nft add table filter

Now create a chain with the command:

nft add chain filter input { type filter hook input priority 0 \; }

Note that the space and backslash before the semi-colon are necessary when entering the command from the command line.

You can now run nft list tables and it will show:

 table filter

Running the following command shows the contents of the table:

 nft list table filter -a

The output will be:

 table ip filter {
chain input {
type filter hook input priority 0;
}
}

That’s it!  You now have nftables running. There are several good tutorials out there that deal with creating an nftables firewall once you’re at this point and I’m also updating my Linux Firewalls book to include coverage of nftables!  It’ll be out in the fall of 2014.