moby--moby/docs/userguide/networking/work-with-networks.md

<!--[metadata]>
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title = "Work with network commands"
description = "How to work with docker networks"
keywords = ["commands, Usage, network, docker, cluster"]
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parent = "smn_networking"
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<![end-metadata]-->

# Work with network commands

This article provides examples of the network subcommands you can use to interact with Docker networks and the containers in them. The commands are available through the Docker Engine CLI.  These commands are:

* `docker network create`
* `docker network connect`
* `docker network ls`
* `docker network rm`
* `docker network disconnect`
* `docker network inspect`

While not required, it is a good idea to read [Understanding Docker
network](dockernetworks.md) before trying the examples in this section. The
examples for the rely on a `bridge` network so that you can try them
immediately.  If you would prefer to experiment with an `overlay` network see
the [Getting started with multi-host networks](get-started-overlay.md) instead.

## Create networks

Docker Engine creates a `bridge` network automatically when you install Engine.
This network corresponds to the `docker0` bridge that Engine has traditionally
relied on. In addition to this network, you can create your own `bridge` or `overlay` network.  

A `bridge` network resides on a single host running an instance of Docker Engine.  An `overlay` network can span multiple hosts running their own engines. If you run `docker network create` and supply only a network name, it creates a bridge network for you.

```bash
$ docker network create simple-network
69568e6336d8c96bbf57869030919f7c69524f71183b44d80948bd3927c87f6a
$ docker network inspect simple-network
[
    {
        "Name": "simple-network",
        "Id": "69568e6336d8c96bbf57869030919f7c69524f71183b44d80948bd3927c87f6a",
        "Scope": "local",
        "Driver": "bridge",
        "IPAM": {
            "Driver": "default",
            "Config": [
                {
                    "Subnet": "172.22.0.0/16",
                    "Gateway": "172.22.0.1/16"
                }
            ]
        },
        "Containers": {},
        "Options": {}
    }
]
```

Unlike `bridge` networks, `overlay` networks require some pre-existing conditions
before you can create one. These conditions are:

* Access to a key-value store. Engine supports Consul Etcd, and ZooKeeper (Distributed store) key-value stores.
* A cluster of hosts with connectivity to the key-value store.
* A properly configured Engine `daemon` on each host in the swarm.

The `docker daemon` options that support the `overlay` network are:

* `--cluster-store`
* `--cluster-store-opt`
* `--cluster-advertise`

It is also a good idea, though not required, that you install Docker Swarm
to manage the cluster. Swarm provides sophisticated discovery and server
management that can assist your implementation.

When you create a network, Engine creates a non-overlapping subnetwork for the
network by default. You can override this default and specify a subnetwork
directly using the the `--subnet` option. On a `bridge` network you can only
specify a single subnet. An `overlay` network supports multiple subnets.

> **Note** : It is highly recommended to use the `--subnet` option while creating
> a network. If the `--subnet` is not specified, the docker daemon automatically
> chooses and assigns a subnet for the network and it could overlap with another subnet
> in your infrastructure that is not managed by docker. Such overlaps can cause
> connectivity issues or failures when containers are connected to that network.

In addition to the `--subnetwork` option, you also specify the `--gateway` `--ip-range` and `--aux-address` options.

```bash
$ docker network create -d overlay
  --subnet=192.168.0.0/16 --subnet=192.170.0.0/16
  --gateway=192.168.0.100 --gateway=192.170.0.100
  --ip-range=192.168.1.0/24
  --aux-address a=192.168.1.5 --aux-address b=192.168.1.6
  --aux-address a=192.170.1.5 --aux-address b=192.170.1.6
  my-multihost-network
```

Be sure that your subnetworks do not overlap. If they do, the network create fails and Engine returns an error.

When creating a custom network, the default network driver (i.e. `bridge`) has additional options that can be passed.
The following are those options and the equivalent docker daemon flags used for docker0 bridge:

| Option                                           | Equivalent  | Description                                           |
|--------------------------------------------------|-------------|-------------------------------------------------------|
| `com.docker.network.bridge.name`                 | -           | bridge name to be used when creating the Linux bridge |
| `com.docker.network.bridge.enable_ip_masquerade` | `--ip-masq` | Enable IP masquerading                                |
| `com.docker.network.bridge.enable_icc`           | `--icc`     | Enable or Disable Inter Container Connectivity        |
| `com.docker.network.bridge.host_binding_ipv4`    | `--ip`      | Default IP when binding container ports               |
| `com.docker.network.mtu`                         | `--mtu`     | Set the containers network MTU                        |
| `com.docker.network.enable_ipv6`                 | `--ipv6`    | Enable IPv6 networking                                |

For example, now let's use `-o` or `--opt` options to specify an IP address binding when publishing ports:

```bash
$ docker network create -o "com.docker.network.bridge.host_binding_ipv4"="172.23.0.1" my-network
b1a086897963e6a2e7fc6868962e55e746bee8ad0c97b54a5831054b5f62672a
$ docker network inspect my-network
[
    {
        "Name": "my-network",
        "Id": "b1a086897963e6a2e7fc6868962e55e746bee8ad0c97b54a5831054b5f62672a",
        "Scope": "local",
        "Driver": "bridge",
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.23.0.0/16",
                    "Gateway": "172.23.0.1/16"
                }
            ]
        },
        "Containers": {},
        "Options": {
            "com.docker.network.bridge.host_binding_ipv4": "172.23.0.1"
        }
    }
]
$ docker run -d -P --name redis --net my-network redis
bafb0c808c53104b2c90346f284bda33a69beadcab4fc83ab8f2c5a4410cd129
$ docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                        NAMES
bafb0c808c53        redis               "/entrypoint.sh redis"   4 seconds ago       Up 3 seconds        172.23.0.1:32770->6379/tcp   redis
```

## Connect containers

You can connect containers dynamically to one or more networks. These networks
can be backed the same or different network drivers. Once connected, the
containers can communicate using another container's IP address or name.

For `overlay` networks or custom plugins that support multi-host
connectivity, containers connected to the same multi-host network but launched
from different hosts can also communicate in this way.

Create two containers for this example:

```bash
$ docker run -itd --name=container1 busybox
18c062ef45ac0c026ee48a83afa39d25635ee5f02b58de4abc8f467bcaa28731

$ docker run -itd --name=container2 busybox
498eaaaf328e1018042c04b2de04036fc04719a6e39a097a4f4866043a2c2152
```

Then create an isolated, `bridge` network to test with.

```bash
$ docker network create -d bridge --subnet 172.25.0.0/16 isolated_nw
06a62f1c73c4e3107c0f555b7a5f163309827bfbbf999840166065a8f35455a8
```

Connect `container2` to the network and then `inspect` the network to verify the connection:

```
$ docker network connect isolated_nw container2
$ docker network inspect isolated_nw
[
    {
        "Name": "isolated_nw",
        "Id": "06a62f1c73c4e3107c0f555b7a5f163309827bfbbf999840166065a8f35455a8",
        "Scope": "local",
        "Driver": "bridge",
        "IPAM": {
            "Driver": "default",
            "Config": [
                {
                    "Subnet": "172.21.0.0/16",
                    "Gateway": "172.21.0.1/16"
                }
            ]
        },
        "Containers": {
            "90e1f3ec71caf82ae776a827e0712a68a110a3f175954e5bd4222fd142ac9428": {
                "Name": "container2",
                "EndpointID": "11cedac1810e864d6b1589d92da12af66203879ab89f4ccd8c8fdaa9b1c48b1d",
                "MacAddress": "02:42:ac:19:00:02",
                "IPv4Address": "172.25.0.2/16",
                "IPv6Address": ""
            }
        },
        "Options": {}
    }
]
```

You can see that the Engine automatically assigns an IP address to `container2`.
Given we specified a `--subnet` when creating the network, Engine picked
an address from that same subnet. Now, start a third container and connect it to
the network on launch using the `docker run` command's `--net` option:

```bash
$ docker run --net=isolated_nw --ip=172.25.3.3 -itd --name=container3 busybox
467a7863c3f0277ef8e661b38427737f28099b61fa55622d6c30fb288d88c551
```

As you can see you were able to specify the ip address for your container.
As long as the network to which the container is connecting was created with
a user specified subnet, you will be able to select the IPv4 and/or IPv6 address(es)
for your container when executing `docker run` and `docker network connect` commands.
The selected IP address is part of the container networking configuration and will be
preserved across container reload. The feature is only available on user defined networks,
because they guarantee their subnets configuration does not change across daemon reload.

Now, inspect the network resources used by `container3`.

```bash
$ docker inspect --format='{{json .NetworkSettings.Networks}}'  container3
{"isolated_nw":{"IPAMConfig":{"IPv4Address":"172.25.3.3"},"NetworkID":"1196a4c5af43a21ae38ef34515b6af19236a3fc48122cf585e3f3054d509679b",
"EndpointID":"dffc7ec2915af58cc827d995e6ebdc897342be0420123277103c40ae35579103","Gateway":"172.25.0.1","IPAddress":"172.25.3.3","IPPrefixLen":16,"IPv6Gateway":"","GlobalIPv6Address":"","GlobalIPv6PrefixLen":0,"MacAddress":"02:42:ac:19:03:03"}}
```
Repeat this command for `container2`. If you have Python installed, you can pretty print the output.

```bash
$ docker inspect --format='{{json .NetworkSettings.Networks}}'  container2 | python -m json.tool
{
    "bridge": {
        "NetworkID":"7ea29fc1412292a2d7bba362f9253545fecdfa8ce9a6e37dd10ba8bee7129812",
        "EndpointID": "0099f9efb5a3727f6a554f176b1e96fca34cae773da68b3b6a26d046c12cb365",
        "Gateway": "172.17.0.1",
        "GlobalIPv6Address": "",
        "GlobalIPv6PrefixLen": 0,
        "IPAMConfig": null,
        "IPAddress": "172.17.0.3",
        "IPPrefixLen": 16,
        "IPv6Gateway": "",
        "MacAddress": "02:42:ac:11:00:03"
    },
    "isolated_nw": {
        "NetworkID":"1196a4c5af43a21ae38ef34515b6af19236a3fc48122cf585e3f3054d509679b",
        "EndpointID": "11cedac1810e864d6b1589d92da12af66203879ab89f4ccd8c8fdaa9b1c48b1d",
        "Gateway": "172.25.0.1",
        "GlobalIPv6Address": "",
        "GlobalIPv6PrefixLen": 0,
        "IPAMConfig": null,
        "IPAddress": "172.25.0.2",
        "IPPrefixLen": 16,
        "IPv6Gateway": "",
        "MacAddress": "02:42:ac:19:00:02"
    }
}
```

You should find `container2` belongs to two networks.  The `bridge` network
which it joined by default when you launched it and the `isolated_nw` which you
later connected it to.

![](images/working.png)

In the case of `container3`, you connected it through `docker run` to the
`isolated_nw` so that container is not connected to `bridge`.

Use the `docker attach` command to connect to the running `container2` and
examine its networking stack:

```bash
$ docker attach container2
```

If you look a the container's network stack you should see two Ethernet interfaces, one for the default bridge network and one for the `isolated_nw` network.

```bash
/ # ifconfig
eth0      Link encap:Ethernet  HWaddr 02:42:AC:11:00:03  
          inet addr:172.17.0.3  Bcast:0.0.0.0  Mask:255.255.0.0
          inet6 addr: fe80::42:acff:fe11:3/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:9001  Metric:1
          RX packets:8 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:648 (648.0 B)  TX bytes:648 (648.0 B)

eth1      Link encap:Ethernet  HWaddr 02:42:AC:15:00:02  
          inet addr:172.25.0.2  Bcast:0.0.0.0  Mask:255.255.0.0
          inet6 addr: fe80::42:acff:fe19:2/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:8 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:648 (648.0 B)  TX bytes:648 (648.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

On the `isolated_nw` which was user defined, the Docker embedded DNS server enables name resolution for other containers in the network.  Inside of `container2` it is possible to ping `container3` by name.

```bash
/ # ping -w 4 container3
PING container3 (172.25.3.3): 56 data bytes
64 bytes from 172.25.3.3: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.25.3.3: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.25.3.3: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.25.3.3: seq=3 ttl=64 time=0.097 ms

--- container3 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms
```

This isn't the case for the default `bridge` network. Both `container2` and  `container1` are connected to the default bridge network. Docker does not support automatic service discovery on this network. For this reason, pinging  `container1` by name fails as you would expect based on the `/etc/hosts` file:

```bash
/ # ping -w 4 container1
ping: bad address 'container1'
```

A ping using the `container1` IP address does succeed though:

```bash
/ # ping -w 4 172.17.0.2
PING 172.17.0.2 (172.17.0.2): 56 data bytes
64 bytes from 172.17.0.2: seq=0 ttl=64 time=0.095 ms
64 bytes from 172.17.0.2: seq=1 ttl=64 time=0.075 ms
64 bytes from 172.17.0.2: seq=2 ttl=64 time=0.072 ms
64 bytes from 172.17.0.2: seq=3 ttl=64 time=0.101 ms

--- 172.17.0.2 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.072/0.085/0.101 ms
```

If you wanted you could connect `container1` to `container2` with the `docker
run --link` command and that would enable the two containers to interact by name
as well as IP.

Detach from a `container2` and leave it running using `CTRL-p CTRL-q`.

In this example, `container2` is attached to both networks and so can talk to
`container1` and `container3`. But `container3` and `container1` are not in the
same network and cannot communicate. Test, this now by attaching to
`container3` and attempting to ping `container1` by IP address.

```bash
$ docker attach container3
/ # ping 172.17.0.2
PING 172.17.0.2 (172.17.0.2): 56 data bytes
^C
--- 172.17.0.2 ping statistics ---
10 packets transmitted, 0 packets received, 100% packet loss

```

You can connect both running and non-running containers to a network. However,
`docker network inspect` only displays information on running containers.

### Linking containers in user-defined networks

In the above example, container_2 was able to resolve container_3's name automatically
in the user defined network `isolated_nw`, but the name resolution did not succeed
automatically in the default `bridge` network. This is expected in order to maintain
backward compatibility with [legacy link](default_network/dockerlinks.md).

The `legacy link` provided 4 major functionalities to the default `bridge` network.

* name resolution
* name alias for the linked container using `--link=CONTAINER-NAME:ALIAS`
* secured container connectivity (in isolation via `--icc=false`)
* environment variable injection

Comparing the above 4 functionalities with the non-default user-defined networks such as
`isolated_nw` in this example, without any additional config, `docker network` provides

* automatic name resolution using DNS
* automatic secured isolated environment for the containers in a network
* ability to dynamically attach and detach to multiple networks
* supports the `--link` option to provide name alias for the linked container

Continuing with the above example, create another container `container_4` in `isolated_nw`
with `--link` to provide additional name resolution using alias for other containers in
the same network.

```bash
$ docker run --net=isolated_nw -itd --name=container4 --link container5:c5 busybox
01b5df970834b77a9eadbaff39051f237957bd35c4c56f11193e0594cfd5117c
```

With the help of `--link` container4 will be able to reach container5 using the
aliased name `c5` as well.

Please note that while creating container4, we linked to a container named `container5`
which is not created yet. That is one of the differences in behavior between the
`legacy link` in default `bridge` network and the new `link` functionality in user defined
networks. The `legacy link` is static in nature and it hard-binds the container with the
alias and it doesnt tolerate linked container restarts. While the new `link` functionality
in user defined networks are dynamic in nature and supports linked container restarts
including tolerating ip-address changes on the linked container.

Now let us launch another container named `container5` linking container4 to c4.

```bash
$ docker run --net=isolated_nw -itd --name=container5 --link container4:c4 busybox
72eccf2208336f31e9e33ba327734125af00d1e1d2657878e2ee8154fbb23c7a
```

As expected, container4 will be able to reach container5 by both its container name and
its alias c5 and container5 will be able to reach container4 by its container name and
its alias c4.

```bash
$ docker attach container4
/ # ping -w 4 c5
PING c5 (172.25.0.5): 56 data bytes
64 bytes from 172.25.0.5: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.25.0.5: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.25.0.5: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.25.0.5: seq=3 ttl=64 time=0.097 ms

--- c5 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms

/ # ping -w 4 container5
PING container5 (172.25.0.5): 56 data bytes
64 bytes from 172.25.0.5: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.25.0.5: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.25.0.5: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.25.0.5: seq=3 ttl=64 time=0.097 ms

--- container5 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms
```

```bash
$ docker attach container5
/ # ping -w 4 c4
PING c4 (172.25.0.4): 56 data bytes
64 bytes from 172.25.0.4: seq=0 ttl=64 time=0.065 ms
64 bytes from 172.25.0.4: seq=1 ttl=64 time=0.070 ms
64 bytes from 172.25.0.4: seq=2 ttl=64 time=0.067 ms
64 bytes from 172.25.0.4: seq=3 ttl=64 time=0.082 ms

--- c4 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.065/0.070/0.082 ms

/ # ping -w 4 container4
PING container4 (172.25.0.4): 56 data bytes
64 bytes from 172.25.0.4: seq=0 ttl=64 time=0.065 ms
64 bytes from 172.25.0.4: seq=1 ttl=64 time=0.070 ms
64 bytes from 172.25.0.4: seq=2 ttl=64 time=0.067 ms
64 bytes from 172.25.0.4: seq=3 ttl=64 time=0.082 ms

--- container4 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.065/0.070/0.082 ms
```

Similar to the legacy link functionality the new link alias is localized to a container
and the aliased name has no meaning outside of the container using the `--link`.

Also, it is important to note that if a container belongs to multiple networks, the
linked alias is scoped within a given network. Hence the containers can be linked to
different aliases in different networks.

Extending the example, let us create another network named `local_alias`

```bash
$ docker network create -d bridge --subnet 172.26.0.0/24 local_alias
76b7dc932e037589e6553f59f76008e5b76fa069638cd39776b890607f567aaa
```

let us connect container4 and container5 to the new network `local_alias`

```
$ docker network connect --link container5:foo local_alias container4
$ docker network connect --link container4:bar local_alias container5
```

```bash
$ docker attach container4

/ # ping -w 4 foo
PING foo (172.26.0.3): 56 data bytes
64 bytes from 172.26.0.3: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.26.0.3: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.26.0.3: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.26.0.3: seq=3 ttl=64 time=0.097 ms

--- foo ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms

/ # ping -w 4 c5
PING c5 (172.25.0.5): 56 data bytes
64 bytes from 172.25.0.5: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.25.0.5: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.25.0.5: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.25.0.5: seq=3 ttl=64 time=0.097 ms

--- c5 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms
```

Note that the ping succeeds for both the aliases but on different networks.
Let us conclude this section by disconnecting container5 from the `isolated_nw`
and observe the results

```
$ docker network disconnect isolated_nw container5

$ docker attach container4

/ # ping -w 4 c5
ping: bad address 'c5'

/ # ping -w 4 foo
PING foo (172.26.0.3): 56 data bytes
64 bytes from 172.26.0.3: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.26.0.3: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.26.0.3: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.26.0.3: seq=3 ttl=64 time=0.097 ms

--- foo ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms

```

In conclusion, the new link functionality in user defined networks provides all the
benefits of legacy links while avoiding most of the well-known issues with `legacy links`.

One notable missing functionality compared to `legacy links` is the injection of
environment variables. Though very useful, environment variable injection is static
in nature and must be injected when the container is started. One cannot inject
environment variables into a running container without significant effort and hence
it is not compatible with `docker network` which provides a dynamic way to connect/
disconnect containers to/from a network.

### Network-scoped alias

While `links` provide private name resolution that is localized within a container,
the network-scoped alias provides a way for a container to be discovered by an
alternate name by any other container within the scope of a particular network.
Unlike the `link` alias, which is defined by the consumer of a service, the
network-scoped alias is defined by the container that is offering the service
to the network.

Continuing with the above example, create another container in `isolated_nw` with a
network alias.

```bash
$ docker run --net=isolated_nw -itd --name=container6 --net-alias app busybox
8ebe6767c1e0361f27433090060b33200aac054a68476c3be87ef4005eb1df17
```

```bash
$ docker attach container4
/ # ping -w 4 app
PING app (172.25.0.6): 56 data bytes
64 bytes from 172.25.0.6: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.25.0.6: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=3 ttl=64 time=0.097 ms

--- app ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms

/ # ping -w 4 container6
PING container5 (172.25.0.6): 56 data bytes
64 bytes from 172.25.0.6: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.25.0.6: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=3 ttl=64 time=0.097 ms

--- container6 ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms
```

Now let us connect `container6` to the `local_alias` network with a different network-scoped
alias.

```
$ docker network connect --alias scoped-app local_alias container6
```

`container6` in this example now is aliased as `app` in network `isolated_nw` and
as `scoped-app` in network `local_alias`.

Let's try to reach these aliases from `container4` (which is connected to both these networks)
and `container5` (which is connected only to `isolated_nw`).

```bash
$ docker attach container4

/ # ping -w 4 scoped-app
PING foo (172.26.0.5): 56 data bytes
64 bytes from 172.26.0.5: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.26.0.5: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.26.0.5: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.26.0.5: seq=3 ttl=64 time=0.097 ms

--- foo ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms

$ docker attach container5

/ # ping -w 4 scoped-app
ping: bad address 'scoped-app'

```

As you can see, the alias is scoped to the network it is defined on and hence only
those containers that are connected to that network can access the alias.

In addition to the above features, multiple containers can share the same network-scoped
alias within the same network. For example, let's launch `container7` in `isolated_nw` with
the same alias as `container6`

```bash
$ docker run --net=isolated_nw -itd --name=container7 --net-alias app busybox
3138c678c123b8799f4c7cc6a0cecc595acbdfa8bf81f621834103cd4f504554
```

When multiple containers share the same alias, name resolution to that alias will happen
to one of the containers (typically the first container that is aliased). When the container
that backs the alias goes down or disconnected from the network, the next container that
backs the alias will be resolved.

Let us ping the alias `app` from `container4` and bring down `container6` to verify that
`container7` is resolving the `app` alias.

```bash
$ docker attach container4
/ # ping -w 4 app
PING app (172.25.0.6): 56 data bytes
64 bytes from 172.25.0.6: seq=0 ttl=64 time=0.070 ms
64 bytes from 172.25.0.6: seq=1 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=2 ttl=64 time=0.080 ms
64 bytes from 172.25.0.6: seq=3 ttl=64 time=0.097 ms

--- app ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.070/0.081/0.097 ms

$ docker stop container6

$ docker attach container4
/ # ping -w 4 app
PING app (172.25.0.7): 56 data bytes
64 bytes from 172.25.0.7: seq=0 ttl=64 time=0.095 ms
64 bytes from 172.25.0.7: seq=1 ttl=64 time=0.075 ms
64 bytes from 172.25.0.7: seq=2 ttl=64 time=0.072 ms
64 bytes from 172.25.0.7: seq=3 ttl=64 time=0.101 ms

--- app ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 0.072/0.085/0.101 ms

```

## Disconnecting containers

You can disconnect a container from a network using the `docker network
disconnect` command.

```
$ docker network disconnect isolated_nw container2

docker inspect --format='{{json .NetworkSettings.Networks}}'  container2 | python -m json.tool
{
    "bridge": {
        "NetworkID":"7ea29fc1412292a2d7bba362f9253545fecdfa8ce9a6e37dd10ba8bee7129812",
        "EndpointID": "9e4575f7f61c0f9d69317b7a4b92eefc133347836dd83ef65deffa16b9985dc0",
        "Gateway": "172.17.0.1",
        "GlobalIPv6Address": "",
        "GlobalIPv6PrefixLen": 0,
        "IPAddress": "172.17.0.3",
        "IPPrefixLen": 16,
        "IPv6Gateway": "",
        "MacAddress": "02:42:ac:11:00:03"
    }
}


$ docker network inspect isolated_nw
[
    {
        "Name": "isolated_nw",
        "Id": "06a62f1c73c4e3107c0f555b7a5f163309827bfbbf999840166065a8f35455a8",
        "Scope": "local",
        "Driver": "bridge",
        "IPAM": {
            "Driver": "default",
            "Config": [
                {
                    "Subnet": "172.21.0.0/16",
                    "Gateway": "172.21.0.1/16"
                }
            ]
        },
        "Containers": {
            "467a7863c3f0277ef8e661b38427737f28099b61fa55622d6c30fb288d88c551": {
                "Name": "container3",
                "EndpointID": "dffc7ec2915af58cc827d995e6ebdc897342be0420123277103c40ae35579103",
                "MacAddress": "02:42:ac:19:03:03",
                "IPv4Address": "172.25.3.3/16",
                "IPv6Address": ""
            }
        },
        "Options": {}
    }
]
```

Once a container is disconnected from a network, it cannot communicate with
other containers connected to that network. In this example, `container2` can no longer  talk to `container3` on the `isolated_nw` network.

```
$ docker attach container2

/ # ifconfig
eth0      Link encap:Ethernet  HWaddr 02:42:AC:11:00:03  
          inet addr:172.17.0.3  Bcast:0.0.0.0  Mask:255.255.0.0
          inet6 addr: fe80::42:acff:fe11:3/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:9001  Metric:1
          RX packets:8 errors:0 dropped:0 overruns:0 frame:0
          TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:648 (648.0 B)  TX bytes:648 (648.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

/ # ping container3
PING container3 (172.25.3.3): 56 data bytes
^C
--- container3 ping statistics ---
2 packets transmitted, 0 packets received, 100% packet loss
```

The `container2` still has full connectivity to the bridge network

```bash
/ # ping container1
PING container1 (172.17.0.2): 56 data bytes
64 bytes from 172.17.0.2: seq=0 ttl=64 time=0.119 ms
64 bytes from 172.17.0.2: seq=1 ttl=64 time=0.174 ms
^C
--- container1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.119/0.146/0.174 ms
/ #
```

There are certain scenarios such as ungraceful docker daemon restarts in multi-host network,
where the daemon is unable to cleanup stale connectivity endpoints. Such stale endpoints
may cause an error `container already connected to network` when a new container is
connected to that network with the same name as the stale endpoint. In order to cleanup
these stale endpoints, first remove the container and force disconnect 
(`docker network disconnect -f`)  the endpoint from the network. Once the endpoint is 
cleaned up, the container can be connected to the network.

```
$ docker run -d --name redis_db --net multihost redis
ERROR: Cannot start container bc0b19c089978f7845633027aa3435624ca3d12dd4f4f764b61eac4c0610f32e: container already connected to network multihost

$ docker rm -f redis_db
$ docker network disconnect -f multihost redis_db

$ docker run -d --name redis_db --net multihost redis
7d986da974aeea5e9f7aca7e510bdb216d58682faa83a9040c2f2adc0544795a
```

## Remove a network

When all the containers in a network are stopped or disconnected, you can remove a network.

```bash
$ docker network disconnect isolated_nw container3
```

```bash
docker network inspect isolated_nw
[
    {
        "Name": "isolated_nw",
        "Id": "06a62f1c73c4e3107c0f555b7a5f163309827bfbbf999840166065a8f35455a8",
        "Scope": "local",
        "Driver": "bridge",
        "IPAM": {
            "Driver": "default",
            "Config": [
                {
                    "Subnet": "172.21.0.0/16",
                    "Gateway": "172.21.0.1/16"
                }
            ]
        },
        "Containers": {},
        "Options": {}
    }
]

$ docker network rm isolated_nw
```

List all your networks to verify the `isolated_nw` was removed:

```
$ docker network ls
NETWORK ID          NAME                DRIVER
72314fa53006        host                host                
f7ab26d71dbd        bridge              bridge              
0f32e83e61ac        none                null  
```

## Related information

* [network create](../../reference/commandline/network_create.md)
* [network inspect](../../reference/commandline/network_inspect.md)
* [network connect](../../reference/commandline/network_connect.md)
* [network disconnect](../../reference/commandline/network_disconnect.md)
* [network ls](../../reference/commandline/network_ls.md)
* [network rm](../../reference/commandline/network_rm.md)