slirp4netns: User-mode networking for unprivileged network namespaces

slirp4netns provides user-mode networking ("slirp") for unprivileged network namespaces.

Latest stable release: v0.2.X

Motivation

Starting with Linux 3.8, unprivileged users can create network_namespaces(7) along with user_namespaces(7). However, unprivileged network namespaces had not been very useful, because creating veth(4) pairs across the host and network namespaces still requires the root privileges. (i.e. No internet connection)

slirp4netns allows connecting a network namespace to the Internet in a completely unprivileged way, by connecting a TAP device in a network namespace to the usermode TCP/IP stack ("slirp").

Projects using slirp4netns

• Usernetes (via RootlessKit)

• Podman

• Buildah

• ctnr (via slirp-cni-plugin)

• RootlessKit

• become-root

• slirp-cni-plugin

Quick start

Install from source

$ ./autogen.sh
$ ./configure --prefix=/usr
$ make
$ sudo make install

• To build slirp4netns as a static binary, please run ./configure with LDFLAGS=-static.
• If you set --prefix to $HOME, you don't need to run make install with sudo.

Install from binary

RHEL 8 & Fedora (28 or later):

$ sudo dnf install slirp4netns

Arch Linux:

If you're running Arch Linux you can install slirp4netns (or slirp4netns-git) from AUR. When you're using an AUR helper (yay, for example) simply use:

yay -S slirp4netns

Otherwise make sure you have base-devel installed and build a package manually:

cd $(mktemp -d)
curl -Lo PKGBUILD "https://aur.archlinux.org/cgit/aur.git/plain/PKGBUILD?h=slirp4netns"
makepkg
sudo pacman -U slirp4netns-*.pkg.tar.*

openSUSE Tumbleweed

$ sudo zypper install slirp4netns

openSUSE Leap 15.0

$ sudo zypper addrepo --refresh http://download.opensuse.org/repositories/devel:/kubic/openSUSE_Leap_15.0/devel:kubic.repo
$ sudo zypper install slirp4netns

SUSE Linux Enterprise 15

$ sudo zypper addrepo --refresh http://download.opensuse.org/repositories/devel:/kubic/SLE_15/devel:kubic.repo
$ sudo zypper install slirp4netns

Debian GNU/Linux Sid

$ sudo apt install slirp4netns

Usage

Terminal 1: Create user/network/mount namespaces

$ unshare --user --map-root-user --net --mount
unshared$ echo $$ > /tmp/pid

Terminal 2: Start slirp4netns

$ slirp4netns --configure --mtu=65520 $(cat /tmp/pid) tap0
starting slirp, MTU=65520
...

Terminal 1: Make sure the tap0 is configured and connected to the Internet

unshared$ ip a
1: lo: <LOOPBACK> mtu 65536 qdisc noop state DOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
3: tap0: <BROADCAST,UP,LOWER_UP> mtu 65520 qdisc fq_codel state UNKNOWN group default qlen 1000
    link/ether c2:28:0c:0e:29:06 brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.100/24 brd 10.0.2.255 scope global tap0
       valid_lft forever preferred_lft forever
    inet6 fe80::c028:cff:fe0e:2906/64 scope link 
       valid_lft forever preferred_lft forever
unshared$ echo "nameserver 10.0.2.3" > /tmp/resolv.conf
unshared$ mount --bind /tmp/resolv.conf /etc/resolv.conf
unshared$ curl https://example.com

See slirp4netns.1.md for further information.

Benchmarks

iperf3 (netns -> host)

Aug 28, 2018, on RootlessKit Travis: rootless-containers/rootlesskit#16

Implementation	MTU=1500	MTU=4000	MTU=16384	MTU=65520
vde_plug	763 Mbps	Unsupported	Unsupported	Unsupported
VPNKit	514 Mbps	526 Mbps	540 Mbps	Unsupported
slirp4netns	1.07 Gbps	2.78 Gbps	4.55 Gbps	9.21 Gbps

slirp4netns is faster than vde_plug and VPNKit because slirp4netns is optimized to avoid copying packets across the namespaces.

The latest revision of slirp4netns is regularly benchmarked (make benchmark) on Travis: https://travis-ci.org/rootless-containers/slirp4netns

Acknowledgement

• The files under qemu directory were forked from QEMU.
• The files under rd235_libslirp directory were forked from rd235/libslirp.
• The files under parson directory were copied from kgabis/parson without any modification.