Configuring Default Bridge Networks, IPv6, and Connection Limits in Docker

[legacy `--link` flag](../links.md). ### Configure the default bridge network To configure the default `bridge` network, you specify options in `daemon.json`. Here is an example `daemon.json` with several options specified. Only specify the settings you need to customize. ```json { "bip": "192.168.1.1/24", "fixed-cidr": "192.168.1.0/25", "mtu": 1500, "default-gateway": "192.168.1.254", "dns": ["10.20.1.2","10.20.1.3"] } ``` In this example: - The bridge's address is "192.168.1.1/24" (from `bip`). - The bridge network's subnet is "192.168.1.0/24" (from `bip`). - Container addresses will be allocated from "192.168.1.0/25" (from `fixed-cidr`). ### Use IPv6 with the default bridge network IPv6 can be enabled for the default bridge using the following options in `daemon.json`, or their command line equivalents. These three options only affect the default bridge, they are not used by user-defined networks. The addresses in below are examples from the IPv6 documentation range. - Option `ipv6` is required. - Option `bip6` is optional, it specifies the address of the default bridge, which will be used as the default gateway by containers. It also specifies the subnet for the bridge network. - Option `fixed-cidr-v6` is optional, it specifies the address range Docker may automatically allocate to containers. - The prefix should normally be `/64` or shorter. - For experimentation on a local network, it is better to use a Unique Local Address (ULA) prefix (matching `fd00::/8`) than a Link Local prefix (matching `fe80::/10`). - Option `default-gateway-v6` is optional. If unspecified, the default is the first address in the `fixed-cidr-v6` subnet. ```json { "ipv6": true, "bip6": "2001:db8::1111/64", "fixed-cidr-v6": "2001:db8::/64", "default-gateway-v6": "2001:db8:abcd::89" } ``` If no `bip6` is specified, `fixed-cidr-v6` defines the subnet for the bridge network. If no `bip6` or `fixed-cidr-v6` is specified, a ULA prefix will be chosen. Restart Docker for changes to take effect. ## Connection limit for bridge networks Due to limitations set by the Linux kernel, bridge networks become unstable and inter-container communications may break when 1000 containers or more connect to a single network. For more information about this limitation, see [moby/moby#44973](https://github.com/moby/moby/issues/44973#issuecomment-1543747718). ## Skip Bridge IP address configuration The bridge is normally assigned the network's `--gateway` address, which is used as the default route from the bridge network to other networks. The `com.docker.network.bridge.inhibit_ipv4` option lets you create a network without the IPv4 gateway address being assigned to the bridge. This is useful if you want to configure the gateway IP address for the bridge manually. For instance if you add a physical interface to your bridge, and need it to have the gateway address. With this configuration, north-south traffic (to and from the bridge network) won't work unless you've manually configured the gateway address on the bridge, or a device attached to it. This option can only be used with user-defined bridge networks. ## Next steps - Go through the [standalone networking tutorial](/manuals/engine/network/tutorials/standalone.md) - Learn about [networking from the container's point of view](../_index.md) - Learn about [overlay networks](./overlay.md) - Learn about [Macvlan networks](./macvlan.md)

This section covers configuring the default bridge network in Docker using `daemon.json`, including setting the bridge IP, subnet, MTU, gateway, and DNS. It also details enabling IPv6 for the default bridge with options like `ipv6`, `bip6`, `fixed-cidr-v6`, and `default-gateway-v6`. Additionally, it mentions the connection limit for bridge networks due to Linux kernel limitations and how to skip the bridge IP address configuration for manual gateway setup. Finally, it provides links to further networking tutorials and documentation.