Packet filtering and firewalls
On Linux, Docker manipulates
iptables rules to provide network isolation.
While this is an implementation detail and you should not modify the rules
Docker inserts into your
iptables policies, it does have some implications
on what you need to do if you want to have your own policies in addition to
those managed by Docker.
If you're running Docker on a host that is exposed to the Internet, you will probably want to have iptables policies in place that prevent unauthorized access to containers or other services running on your host. This page describes how to achieve that, and what caveats you need to be aware of.
Docker installs two custom
iptables chains named
and it ensures that incoming packets are always checked by these two chains
first. These chains are part of the
All of Docker's
iptables rules are added to the
DOCKER chain. Do not
manipulate this chain manually. If you need to add rules which load before
Docker's rules, add them to the
DOCKER-USER chain. These rules are applied
before any rules Docker creates automatically.
Other rules added to the
FORWARD chain, either manually, or by another
iptables-based firewall, are evaluated after the
This means that if you publish a port through Docker,
this port gets published no matter what rules your firewall has configured.
If you want rules to apply even when a port gets published through Docker,
you must add these rules to the
When packets arrive to the
DOCKER-USER chain, they have already passed through
a Destination Network Address Translation (DNAT) filter. That means that the
iptables flags you use can only match internal IP addresses and ports of
If you want to match traffic based on the original IP and port in the network
request, you must use the
conntrack iptables extension.
$ sudo iptables -I DOCKER-USER -p tcp -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
$ sudo iptables -I DOCKER-USER -p tcp -m conntrack --ctorigsrc 22.214.171.124 --ctorigdstport 80 -j ACCEPT
conntrackextension may result in degraded performance.
By default, all external source IPs are allowed to connect to the Docker host.
To allow only a specific IP or network to access the containers, insert a
negated rule at the top of the
DOCKER-USER filter chain. For example, the
following rule restricts external access from all IP addresses except
$ iptables -I DOCKER-USER -i ext_if ! -s 192.168.1.1 -j DROP
You will need to change
ext_if to correspond with your
host's actual external interface. You could instead allow connections from a
source subnet. The following rule only allows access from the subnet
$ iptables -I DOCKER-USER -i ext_if ! -s 192.168.1.0/24 -j DROP
Finally, you can specify a range of IP addresses to accept using
(Remember to also add
-m iprange when using
$ iptables -I DOCKER-USER -m iprange -i ext_if ! --src-range 192.168.1.1-192.168.1.3 -j DROP
You can combine
--dst-range to control both
the source and destination. For instance, if the Docker daemon listens on both
10.1.2.3, you can make rules specific to
10.1.2.3 and leave
iptables is complicated and more complicated rules are out of scope for this
topic. See the
for a lot more information.
Docker also sets the policy for the
FORWARD chain to
DROP. If your Docker
host also acts as a router, this will result in that router not forwarding
any traffic anymore. If you want your system to continue functioning as a
router, you can add explicit
ACCEPT rules to the
DOCKER-USER chain to
$ iptables -I DOCKER-USER -i src_if -o dst_if -j ACCEPT
It is possible to set the
iptables key to
false in the Docker engine's configuration file at
/etc/docker/daemon.json, but this option is not appropriate for most users. It is not possible to completely prevent Docker from creating
iptables rules, and creating them after-the-fact is extremely involved and beyond the scope of these instructions. Setting
false will more than likely break container networking for the Docker engine.
For system integrators who wish to build the Docker runtime into other applications, explore the
By default, the Docker daemon binds published container ports to the
address. When you publish a container's ports as follows:
docker run -p 8080:80 nginx
This publishes port 8080 to all network interfaces on the host, potentially making them available to the outside world. Unless you've disabled IPv6 at the kernel level, the port gets published on both IPv4 and IPv6.
You can change the default binding address for published container ports so that
they're only accessible to the Docker host by default. To do that, you can
configure the daemon to use the loopback address (
To do so, configure the
"ip" key in the
daemon.json configuration file:
This changes the default binding address to
127.0.0.1 for published container
ports on the default bridge network.
Restart the daemon for this change to take effect.
Alternatively, you can use the
dockerd --ip flag when starting the daemon.
Changing the default bind address doesn't have any effect on Swarm services. Swarm services are always exposed on the
To configure this setting for user-defined bridge networks, use
driver option when you create the network.
$ docker network create mybridge \
If you are running Docker with
on your system with
--iptables enabled, Docker automatically creates a
docker and inserts all the network interfaces it creates (for example,
docker0) into the
docker zone to allow seamless networking.
Uncomplicated Firewall (ufw) is a frontend that ships with Debian and Ubuntu, and it lets you manage firewall rules. Docker and ufw use iptables in ways that make them incompatible with each other.
When you publish a container's ports using Docker, traffic to and from that
container gets diverted before it goes through the ufw firewall settings.
Docker routes container traffic in the
nat table, which means that packets
are diverted before it reaches the
OUTPUT chains that ufw uses.
Packets are routed before the firewall rules can be applied,
effectively ignoring your firewall configuration.