> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Demo Docker Network
> This lesson explores Docker networking fundamentals including default networks, custom bridge networks, DNS resolution, and connecting or disconnecting containers from networks.
In this lesson, we’ll explore Docker networking fundamentals: default networks, custom bridge networks, DNS resolution, and how to connect or disconnect containers from networks. By the end, you’ll understand how Docker manages container networking and how to customize it for your applications.
## Listing Default Networks
Docker comes with three built-in networks:
| Network | Driver | Scope | Description |
| ------- | ------ | ----- | -------------------------------------------- |
| bridge | bridge | local | Default network for newly created containers |
| host | host | local | Container shares the host’s network stack |
| none | null | local | No networking; containers are isolated |
To see these networks:
```bash theme={null}
docker network ls
```
Example output:
```bash theme={null}
$ docker network ls
NETWORK ID NAME DRIVER SCOPE
cf10938f5edf bridge bridge local
d4f46412e7e9 host host local
b5b0ab8c1665 none null local
```
## Inspecting the Bridge Network
To view details such as subnet configuration and gateway:
```bash theme={null}
docker network inspect bridge
```
Key fields:
```json theme={null}
[
{
"Name": "bridge",
"Driver": "bridge",
"IPAM": {
"Config": [
{
"Subnet": "172.17.0.0/16",
"Gateway": "172.17.0.1"
}
]
},
"Options": {
"com.docker.network.bridge.default_bridge": "true",
"com.docker.network.bridge.enable_icc": "true",
"com.docker.network.bridge.enable_ip_masquerade": "true",
"com.docker.network.bridge.host_binding_ipv4": "0.0.0.0"
}
}
]
```
The IPAM (IP Address Management) section shows how Docker assigns subnets and gateways.
## Running Containers on the Default Bridge
When you start a container without specifying a network, it’s attached to `bridge`:
```bash theme={null}
docker run -itd --name first centos:7
```
Inspect its network settings:
```bash theme={null}
docker inspect first --format '{{json .NetworkSettings}}' | jq
```
```json theme={null}
{
"Gateway": "172.17.0.1",
"IPAddress": "172.17.0.2",
"IPPrefixLen": 16,
"MacAddress": "02:42:ac:11:00:02",
"Networks": {
"bridge": {
"IPAddress": "172.17.0.2",
"Gateway": "172.17.0.1",
"MacAddress": "02:42:ac:11:00:02"
}
}
}
```
Create a second container:
```bash theme={null}
docker run -itd --name second centos:7
```
On the default bridge, embedded DNS is **not** enabled. Attempting to ping by container name fails:
```bash theme={null}
docker exec first ping -c 2 second
# ping: second: Name or service not known
```
## Creating a User-Defined Bridge Network
User-defined bridge networks include built-in DNS and automatic name resolution. Create one with a custom subnet:
```bash theme={null}
docker network create \
--driver bridge \
--subnet 192.168.10.0/24 \
kodekloudnet
```
Verify its presence:
```bash theme={null}
docker network ls
```
```bash theme={null}
$ docker network ls
NETWORK ID NAME DRIVER SCOPE
cf10938f5edf bridge bridge local
d4f46412e7e9 host host local
f22c791ef1ad kodekloudnet bridge local
b5b0ab8c1665 none null local
```
## Running Containers on the Custom Network
Launch two containers on `kodekloudnet`:
```bash theme={null}
docker run -itd --name customfirst --net kodekloudnet centos:7
docker run -itd --name customsecond --net kodekloudnet centos:7
```
They now receive IPs within `192.168.10.0/24`, and DNS-based name resolution works:
```bash theme={null}
docker exec customfirst ping -c 4 customsecond
```
```bash theme={null}
PING customsecond (192.168.10.3): 56 data bytes
64 bytes from customsecond.kodekloudnet (192.168.10.3): icmp_seq=1 ttl=64 time=0.07 ms
...
```
## Connecting an Existing Container to a Network
By default, containers attach only to the default bridge. To connect `first` to `kodekloudnet`:
```bash theme={null}
docker network connect kodekloudnet first
```
Verify both network endpoints:
```bash theme={null}
docker inspect first \
--format '{{json .NetworkSettings.Networks}}' | jq
```
```json theme={null}
{
"bridge": {
"IPAddress": "172.17.0.2"
},
"kodekloudnet": {
"IPAddress": "192.168.10.4"
}
}
```
Now ping `first` from `customfirst`:
```bash theme={null}
docker exec customfirst ping -c 2 first
```
## Disconnecting a Container from a Network
To detach a container:
```bash theme={null}
docker network disconnect kodekloudnet first
```
After disconnecting, `customfirst` will no longer reach `first` on that network.
## Removing Networks
Docker prevents removing networks with active endpoints. To delete `kodekloudnet`:
1. Stop and remove containers:
```bash theme={null}
docker container stop $(docker ps -q)
docker container rm $(docker ps -aq)
```
2. Remove the network:
```bash theme={null}
docker network rm kodekloudnet
```
You can also prune all unused user-defined networks:
```bash theme={null}
docker network prune
```
`docker network prune` removes only user-defined networks without active containers. Default networks (`bridge`, `host`, `none`) are not affected.
***
## Links and References
* [Docker Networking Overview](https://docs.docker.com/network/)
* [Docker Network Commands](https://docs.docker.com/engine/reference/commandline/network/)
* [Kubernetes Networking](https://kubernetes.io/docs/concepts/services-networking/)