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Network Configuration: Customizing Your Networks

Default networks work. But sometimes you need more. Custom subnets. Specific IPs. DNS settings. That's network configuration.

🎯 The Big Picture​

Think of network configuration like customizing a house. The default house works. But you might want a bigger garage (larger subnet). A specific address (fixed IP). Better security (firewall rules). Custom features.

Network configuration gives you control. You decide how networks work.

Creating Networks with Configuration​

Basic network creation:

docker network create my-network

That's it. Works. But you can configure more.

Custom Subnet​

Set your own subnet:

docker network create --subnet=192.168.100.0/24 my-network

What it does:

  • Creates network with subnet 192.168.100.0/24
  • Containers get IPs from 192.168.100.2 to 192.168.100.254
  • Gateway is 192.168.100.1

Why use custom subnet?

  • Avoid conflicts with existing networks
  • Organize by application
  • Match your network architecture
  • Specific IP ranges

Think of it as: Choosing a specific neighborhood. Not random. You decide the address range.

Example:

# Create network with custom subnet
docker network create --subnet=10.0.1.0/24 app-network

# Containers get IPs like 10.0.1.2, 10.0.1.3, etc.
docker run -d --name web --network app-network nginx

Custom Gateway​

Set custom gateway:

docker network create \
  --subnet=192.168.100.0/24 \
  --gateway=192.168.100.1 \
  my-network

What it does:

  • Sets gateway IP to 192.168.100.1
  • Default is usually .1 in subnet
  • Can customize if needed

Why customize gateway?

  • Match existing network architecture
  • Specific routing requirements
  • Network integration

IP Address Ranges​

Set IP address range:

docker network create \
  --subnet=192.168.100.0/24 \
  --ip-range=192.168.100.0/28 \
  my-network

What it does:

  • Network subnet: 192.168.100.0/24 (256 addresses)
  • IP range for containers: 192.168.100.0/28 (16 addresses)
  • Limits container IPs to specific range

Why limit IP range?

  • Reserve IPs for other uses
  • Better organization
  • Network planning

Think of it as: Reserving some addresses. Not all addresses are for containers. Some are reserved.

DNS Configuration​

Configure DNS servers:

docker network create \
  --dns=8.8.8.8 \
  --dns=8.8.4.4 \
  my-network

What it does:

  • Sets DNS servers for containers
  • Default: Docker's built-in DNS
  • Can use external DNS (Google, Cloudflare, etc.)

Why customize DNS?

  • Use company DNS
  • Specific DNS requirements
  • DNS filtering
  • Performance optimization

Multiple DNS servers:

docker network create \
  --dns=8.8.8.8 \
  --dns=1.1.1.1 \
  --dns-search=example.com \
  my-network

--dns-search: Adds search domain. Containers can resolve web as web.example.com.

Driver Options​

Configure driver-specific options:

# Bridge driver options
docker network create \
  --driver bridge \
  -o com.docker.network.bridge.name=my-bridge \
  -o com.docker.network.bridge.enable_icc=true \
  my-network

Common options:

  • com.docker.network.bridge.name: Bridge name
  • com.docker.network.bridge.enable_icc: Inter-container communication
  • com.docker.network.bridge.enable_ip_masquerade: IP masquerading

Why configure driver options?

  • Advanced networking requirements
  • Integration with existing networks
  • Specific network behavior

Labels​

Add labels to networks:

docker network create \
  --label environment=production \
  --label app=web \
  my-network

What it does:

  • Adds metadata to network
  • Useful for organization
  • Can filter by labels

Why use labels?

  • Organization
  • Automation
  • Filtering
  • Documentation

Filter by labels:

docker network ls --filter "label=environment=production"

The House Customization Analogy​

Think of network configuration like customizing a house:

Custom subnet: Choosing a specific neighborhood

  • Not random
  • You decide the address range

Custom gateway: Setting the main entrance

  • Where traffic enters/exits
  • Routing point

IP range: Reserving some rooms

  • Not all addresses for containers
  • Some reserved

DNS configuration: Setting up phone directory

  • How to find addresses
  • Which directory to use

Driver options: Advanced features

  • Custom bridge settings
  • Advanced networking

Labels: Adding tags

  • Organization
  • Filtering

Once you see it this way, network configuration makes sense.

Real-World Example: Production Network Setup​

Let me show you a real production setup:

1. Create network for web application:

docker network create \
  --subnet=10.0.1.0/24 \
  --gateway=10.0.1.1 \
  --dns=8.8.8.8 \
  --label environment=production \
  --label app=web \
  web-network

2. Create network for database:

docker network create \
  --subnet=10.0.2.0/24 \
  --gateway=10.0.2.1 \
  --label environment=production \
  --label app=database \
  db-network

3. Run containers:

# Web on web-network
docker run -d --name web --network web-network nginx

# Database on db-network
docker run -d --name db --network db-network postgres

Why this setup?

  • Separate networks for isolation
  • Custom subnets for organization
  • Labels for management
  • Production-ready

Inspecting Network Configuration​

See network details:

# Inspect network
docker network inspect my-network

# Get specific information
docker network inspect -f '{{.IPAM.Config}}' my-network

Shows:

  • Subnet
  • Gateway
  • Containers
  • Configuration
  • Everything!

Updating Network Configuration​

Note: You can't modify network configuration after creation. You need to:

  1. Remove containers
  2. Remove network
  3. Create new network with new configuration
  4. Recreate containers

That's why planning is important.

My Take: Network Configuration Strategy​

Here's what I do:

Development:

  • Use default networks
  • Simple and works
  • No configuration needed

Production:

  • Custom subnets per application
  • Labels for organization
  • DNS configuration if needed
  • Plan before creating

The key: Start simple. Configure only when needed. Plan production networks carefully.

Memory Tip: The House Customization Analogy​

Network configuration = House customization

Subnet: Choose neighborhood Gateway: Set main entrance IP range: Reserve rooms DNS: Set phone directory Options: Advanced features Labels: Add tags

Once you see it this way, configuration makes sense.

Common Mistakes​

  1. Over-configuring: Defaults work for most cases
  2. Not planning subnets: IP conflicts
  3. Forgetting labels: Hard to organize later
  4. Wrong subnet size: Too small or too large
  5. Not documenting: Forget why you configured it

Hands-On Exercise: Configure a Network​

1. Create network with custom subnet:

docker network create \
  --subnet=192.168.200.0/24 \
  --gateway=192.168.200.1 \
  my-custom-network

2. Inspect it:

docker network inspect my-custom-network

3. Run container on it:

docker run -d --name test --network my-custom-network alpine sleep 3600

4. Check IP:

docker inspect -f '{{.NetworkSettings.Networks.my-custom-network.IPAddress}}' test
# Should be in 192.168.200.x range

5. Clean up:

docker stop test
docker rm test
docker network rm my-custom-network

Key Takeaways​

  1. Custom subnet - Choose your IP range
  2. Custom gateway - Set routing point
  3. IP ranges - Reserve addresses
  4. DNS configuration - Set DNS servers
  5. Labels - Organize networks
  6. Plan before creating - Can't modify after creation

What's Next?​

Now that you can configure networks, let's learn about service discovery. Next: Service Discovery.

Remember: Network configuration gives you control. But start simple. Configure only when you need to. Defaults work for most cases.