---
name: "interfaces-bridge"
section: "5"
platform: "linux"
package: "ifupdown-ng"
version: "0.12.1-7"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/interfaces-bridge"
---

# interfaces-bridge(5)

Bridge extensions for the interfaces(5) file format

## NAME

**interfaces-bridge** - Bridge extensions for the [interfaces(5)](/interfaces/5.md) file format

## DESCRIPTION

Linux has support for Ethernet bridging interfaces which act like an Ethernet switch within the Linux Kernel. The following options allow to set up Ethernet bridges and adding configured interfaces to bridges.

See [**ip-link**(8)](/ip-link/8.md) for more details about the options listed below.

## BRIDGE-RELATED OPTIONS

**bridge-ports** *list of interfaces*

A space separated list of interfaces which should be configured as member interfaces of this bridge. This option must be set for the bridge to be configured.

**bridge-hw** *MAC address*

Denotes the *MAC address* the bridge should use.

**bridge-ageing** *seconds*

Denotes the time in seconds after which a MAC address will be removed from the Forwarding DataBase (FDB) after not having seen a frame with this source address.

**bridge-vlan-aware** *bool*

Denotes wether or not the bridge should be aware of 802.1q VLANs. *bool* can be given as *yes*/*no* or *0*/*1*.  The defaul is *no*. See related options for configuring vlan-aware bridges, below.

## SPANNING TREE RELATED BRIDGE OPTIONS

**bridge-stp** *state*

Activates or deactivates IEEE 802.1d Spanning Tree Protocol (STP) support of the bridge. Valid values are *on*/*off*.

**bridge-bridgeprio** *priority*

Sets the bridge's priority to *priority*. The priority value is a number between 0 and 65535. Lower priority values are better. The bridge with the lowest priority will be elected *root* *bridge*.

**bridge-fd** *seconds*

Denotes the bridge forward delay in seconds. Valid values are between 2 and 30.

**bridge-hello** *seconds*

Denotes the bridge hello time in seconds. Valid values are between 1 and 10.

**bridge-maxage** *seconds*

Denotes the seconds until another bridge is considerd dead after reception of its last STP hello message. Valid values are between 6 and 40.

## OPTIONS FOR VLAN-AWARE-BRIDGES

The following options only have an effect on vlan-aware bridges and their ports.

All settings can be applied on the bridge interface itself and all member port iface stanzas.  If applied on the bridge interface they take effect for the bridge interface itself and might be inherited to *bridge-ports* depending on the compatibility settings configured in [**ifupdown-ng.conf**(5)](/ifupdown-ng.conf/5.md).

Configuring VLAN options on the bridge interface might be required for setting up a VLAN interface to one of the VLANs carried within the bridge. See the EXAMPLES section for an example for this scenario.

See [**ifupdown-ng.conf**(5)](/ifupdown-ng.conf/5.md) for more information about compatiblity settings mentioned below.

**bridge-access** *vlan ID*

Configure the given *vlan ID* for untagged ingress and egress on this interface.  The common description for this kind of configuration is called "access port".

**bridge-pvid** *vlan ID*

Denotes the *vlan ID* to considered a PVID at ingress. Any untagged frames received on this interface will be assigned to this *vlan ID*.  The default PVID is *1*.

If compatibility to ifupdown2 bridge port inheritance is active a *bridge-pvid* set on the bridge will be inherited to any interface configured in *bridge-ports* without a *bridge-pvid* set.

**bridge-vids** *list of vlan IDs*

Denotes the space separated list of VLANs to be allowed tagged ingress/egress on this interface.

If compatibility to ifupdown2 bridge port inheritance is active a *bridge-vids* set on the bridge will be inherited to any interface configured in *bridge-ports* without *bridge-vids* set.

**bridge-allow-untagged** *bool*

Denotes wether or not the bridge should allow untagged frames on ingress as well as egress. If set to *no* untagged frames will be droppped on ingress and none will be sent. *bool* can be given as *yes*/*no* or *0*/*1*.  The defaul is *yes*.

## EXAMPLES

A simple layer 2 only bridge:

```
auto br0
iface br0
	bridge-ports eth0 veth-vm1 tap0
	bridge-fd 0
	bridge-stp off
```

A bridge with layer 3 configuration:

```
auto br0
iface br0
	bridge-ports eth0 veth-vm1 tap0
	bridge-fd 0
	bridge-stp off
	#
	address 192.0.2.42/24
	address 2001:db8::42/64
```

A layer 2 only vlan-aware bridge:

```
auto bond0
iface bond0
	bond-members eth0 eth1
	bridge-vids 23 42 84 1337
auto br0
iface br0
	bridge-ports bond0
```

A vlan-aware bridge with a VLAN interface on top:

```
auto eth0
iface eth0
	bridge-vids 23 42 84 1337
auto br0
iface br0
	bridge-ports eth0
	bridge-vlan-aware yes
	bridge-vids 42
auto vlan42
iface vlan42
	vlan-raw-device br0
	#
	address 192.0.2.42/24
	address 2001:db8::42/64
```

## SEE ALSO

[**interfaces**(5)](/interfaces/5.md) [**ifupdown-ng.conf**(5)](/ifupdown-ng.conf/5.md) [**ip-link**(8)](/ip-link/8.md) [**bridge**(8)](/bridge/8.md)

## AUTHORS

Maximilian Wilhelm \<max@sdn.clinic\>