1. First Principles: What Is Docker Networking?

Docker networking is the system that allows:

• Container ↔ Container communication
• Container ↔ Host communication
• External ↔ Container communication
• Network isolation between groups of containers

Under the hood, Docker uses:

• Linux network namespaces
• Virtual ethernet interfaces (Veth pairs)
• Linux bridges
• iptables rules

Every container gets its own network namespace (isolated network stack).

2. What Happens When You Run Docker Compose

When you run:

docker compose up

Docker Compose automatically:

1. Creates a bridge network:

   <project_name>_default
   

2. Connects all services to it.