---
source: https://iinventedlight.com/library/notes/docker-bridge-networks.md
title: "Docker networking: the default bridge and bridge networks"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "Docker docs, Apache-2.0 (github.com/docker/docs; https://github.com/docker/docs/blob/main/LICENSE); Docker name and logo are trademarks of Docker Inc and are not licensed; prose restates or closely paraphrases cited source lines"
license_family: docker-docs-apache
rule_check: "needs rule check (family not in auto-publish rule; check.mjs auto-approves only usgov and arxiv-ccby)"
attribution: "Summary by iinventedlight (AI-assisted). Sources: Docker Docs, Networking overview, Docker docs, Apache-2.0 (github.com/docker/docs; https://github.com/docker/docs/blob/main/LICENSE); Docker name and logo are trademarks of Docker Inc and are not licensed; Docker Docs, Bridge network driver, Docker docs, Apache-2.0 (github.com/docker/docs; https://github.com/docker/docs/blob/main/LICENSE); Docker name and logo are trademarks of Docker Inc and are not licensed."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No code was run for this note; only the fetched documentation pages were read."
category: coding-references
topic_area: "code-ai-eng: Docker"
tags: ['docker', 'networking', 'bridge']
sources:
  - id: S1
    title: "Networking overview"
    publisher: Docker Docs
    url: https://docs.docker.com/engine/network/
    accessed: 2026-11-04
    license: "Docker docs, Apache-2.0 (github.com/docker/docs; https://github.com/docker/docs/blob/main/LICENSE); Docker name and logo are trademarks of Docker Inc and are not licensed"
  - id: S2
    title: "Bridge network driver"
    publisher: Docker Docs
    url: https://docs.docker.com/engine/network/drivers/bridge/
    accessed: 2026-11-04
    license: "Docker docs, Apache-2.0 (github.com/docker/docs; https://github.com/docker/docs/blob/main/LICENSE); Docker name and logo are trademarks of Docker Inc and are not licensed"
---
# Docker networking: the default bridge and bridge networks

**Answer:** When Docker Engine on Linux starts for the first time, it has a single built-in network called the "default bridge" network. When you run a container without the --network option, it is connected to the default bridge. (S1)

## What a container sees

- Containers have networking enabled by default, and they can make outgoing connections. (S1)
- A container has no information about what kind of network it's attached to, or whether its network peers are also Docker containers. (S1)
- A container only sees a network interface with an IP address, a gateway, a routing table, DNS services, and other networking details. (S1)
- With the default configuration, containers attached to the default bridge network have unrestricted network access to each other using container IP addresses. (S1)

## Bridge networks

- A Docker bridge network has an IPv4 subnet and, optionally, an IPv6 subnet. (S2)
- A bridge network uses a software bridge which lets containers connected to the same bridge network communicate, while providing isolation from containers that aren't connected to that bridge network. (S2)
- By default, containers connected to different bridge networks can only communicate with each other using published ports. (S2)
- Devices on the host's external networks only see the IP address of the Docker host. (S2)
- Bridge networks apply to containers running on the same Docker daemon host; across hosts, you can manage routing at the OS level or use an overlay network. (S2)

## Claims
- id: C1
  claim: Docker Engine on Linux starts with a default bridge network.
  source: S1
  evidence: "to run a container on the default bridge network"
- id: C2
  claim: Containers without --network join the default bridge.
  source: S1
  evidence: "When you run a container without the --network option"
- id: C3
  claim: A bridge network has an IPv4 subnet and optionally an IPv6 subnet.
  source: S2
  evidence: "A Docker bridge network has an IPv4 subnet and, optionally, an IPv6 subnet."
- id: C4
  claim: Bridge networks apply to one Docker daemon host.
  source: S2
  evidence: "Bridge networks apply to containers running on the same Docker daemon host."

## Sources
- [S1] Networking overview. Docker Docs. https://docs.docker.com/engine/network/ . License: Docker docs, Apache-2.0 (github.com/docker/docs; https://github.com/docker/docs/blob/main/LICENSE); Docker name and logo are trademarks of Docker Inc and are not licensed. Accessed 2026-11-04.
- [S2] Bridge network driver. Docker Docs. https://docs.docker.com/engine/network/drivers/bridge/ . License: Docker docs, Apache-2.0 (github.com/docker/docs; https://github.com/docker/docs/blob/main/LICENSE); Docker name and logo are trademarks of Docker Inc and are not licensed. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).