Imagine a small neighborhood where houses (containers) are connected by private roads (bridge network). The residents can visit each other easily, but outsiders need a special gate (port mapping) to enter. This is how Docker’s bridge network works - it connects containers internally while controlling access from the outside world.

Bridge Netwrork Foundations

1. What is a Bridge Network?

• A bridge network is Docker’s default networking mode.
• It creates a private internal network on the host machine.
• Containers attached to the bridge network can communicate with each other using IP addresses or container names.
• External access requires explicit port mapping.

2. Characteristics of Bridge Networks

• Isolation: Containers in the bridge network are isolated from the host and other networks.
• Name Resolution: Containers can resolve each other by name using Docker’s built‑in DNS.
• Port Mapping: Required to expose container services externally.
• Flexibility: Multiple containers can join the same bridge network and communicate seamlessly.

3. Default vs Custom Bridge Networks

• Default Bridge Network:
  • Automatically created by Docker (bridge).
  • Containers can connect but must use IP addresses.
• Custom Bridge Network:
  • Created by users for better control.
  • Provides automatic name resolution (containers can use names instead of IPs).

4. Bridge Network Workflow

1. User runs a container.
2. Docker attaches it to the default bridge network.
3. Containers can talk internally but need port mapping for external communication.
4. Custom bridge networks allow easier service discovery.

Things to Remember

• Bridge is the default network mode for containers.
• Port mapping is essential for external access.
• Custom bridge networks improve usability with name‑based communication.

Hands‑On Lab

Step 1: Run a Container in the Default Bridge Network

docker run -d --name web1 nginx

Step 2: Inspect the Network

docker network inspect bridge

• Shows connected containers and IP addresses.

Step 3: Create a Custom Bridge Network

docker network create mybridge

Step 4: Run Containers in the Custom Network

docker run -d --network=mybridge --name web nginx
docker run -d --network=mybridge --name db redis

Step 5: Test Communication

docker exec -it web ping db

• web can resolve db by name.

Step 6: Expose Ports for External Access

docker run -d --network=mybridge -p 8080:80 --name webapp nginx

• Access Nginx at http://localhost:8080.

Practice Exercise

1. Create a custom bridge network called appnet.
2. Run three containers (frontend, backend, database) in appnet.
3. Test communication between them using container names.
4. Expose the frontend container on port 8081 and access it in your browser.

Visual Learning Model

Host Machine
   ↓
Bridge Network
   ├── Container A (frontend) → Port 8081
   ├── Container B (backend)  → Internal only
   └── Container C (database) → Internal only

The Hackers Notebook

Bridge networks are Docker’s default networking mode, enabling containers to communicate internally while requiring port mapping for external access. Custom bridge networks enhance usability by allowing name‑based communication, making them ideal for multi‑container applications.