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SLIRP4NETNS(1) User Commands SLIRP4NETNS(1)

NAME

slirp4netns - User-mode networking for unprivileged network namespaces

SYNOPSIS

slirp4netns [OPTION]... PID TAPNAME

DESCRIPTION

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

Unlike veth(4), slirp4netns does not require the root privileges on the host.

Default configuration:

  • Gateway: 10.0.2.2, fd00::2
  • DNS: 10.0.2.3, fd00::3
  • Host: 10.0.2.2, 10.0.2.3, fd00::2, fd00::3

OPTIONS

-c, --configure bring up the interface. IP will be set to 10.0.2.100. IPv6 will be set to a random address.

-e, --exit-fd=FD specify the FD for terminating slirp4netns.

-r, --ready-fd=FD specify the FD to write to when the network is configured.

-m, --mtu=MTU specify MTU (default=1500, max=65521).

-6, --enable-ipv6 enable IPv6 (experimental).

-h, --help show help and exit

-v, --version show version and exit

EXAMPLE

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 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

Bind-mounting /etc/resolv.conf is only needed when /etc/resolv.conf on the host refers to loopback addresses (127.0.0.X, typically because of dnsmasq(8) or systemd-resolved.service(8)) that cannot be accessed from the namespace.

If your /etc/resolv.conf on the host is managed by networkmanager(8) or systemd-resolved.service(8), you might need to mount a new filesystem on /etc instead, so as to prevent the new /etc/resolv.conf from being unmounted unexpectedly when /etc/resolv.conf on the host is regenerated.

unshared$ mkdir /tmp/a /tmp/b
unshared$ mount --rbind /etc /tmp/a
unshared$ mount --rbind /tmp/b /etc
unshared$ mkdir /etc/.ro
unshared$ mount --move /tmp/a /etc/.ro
unshared$ cd /etc
unshared$ for f in .ro/*; do ln -s $f $(basename $f); done
unshared$ rm resolv.conf
unshared$ echo "nameserver 10.0.2.3" > /tmp/resolv.conf
unshared$ curl https://example.com

ROUTING PING PACKETS

To route ping packets, you need to set up net.ipv4.ping_group_range properly as the root.

e.g.

$ sudo sh -c "echo 0   2147483647  > /proc/sys/net/ipv4/ping_group_range"

SEE ALSO

network_namespaces(7), user_namespaces(7), veth(4)

AVAILABILITY

The slirp4netns command is available from https://github.com/rootless-containers/slirp4netns under GNU GENERAL PUBLIC LICENSE Version 2.
July 2018 Rootless Containers