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Configuration of a bridge in connection with eth interfaces

Last adaptation to the version: 11.8.7


Previous versions: 11.7

A bridge (network bridge) connects two physical networks to a common one.
The interfaces connected in this way have an IP and the IP addresses of the connected devices are in the same subnet

The firewall must not be administered via the interface that is to be added to a bridge! The connection to the admin interface is lost as soon as the IP address is removed from the interface currently used to access the UTM.
If all available internal interfaces are to be added to a bridge (e.g. eth1 and eth2 for a Black Dwarf), external access to the firewall must be via eth0.

Port forwarding from an internal network via an external IP address is not possible via a bridge. This could be remedied by setting up a forward zone in the UTM name server, provided that the UTM is set up as the name server for the internal clients. In this case, the external URL called by Internal refers directly to the internal target server. Instructions for setting up the forward zone can be found under Forward-Zone in the Nameserver Wiki.

Prepare administration access

  • Identify an interface on the firewall that should not be bridged.
  • In the menu → Network →Network Configuration IP Addresses note down or assign existing IP address of this interface (e.g. or
  • Find a free IP address from the corresponding network.
  • Add this IP address or the entire associated network (e.g. or in the menu → Network →Server Settings tab Administration Add IP / Network and authorize it for administration
  • Establish access on the selected interface via this IP address or this network (e.g.: or

Prepare interfaces

Removing ip address

First, remove all IP addresses from the interfaces to be used for the bridge.
→ Network →Network Configuration in the corresponding interface → Tab IP Addresses.
Remove IP addresses. In the example » by clicking on
Under no circumstances may the IP address be removed which is used for the current access !

In the second step, all zones are removed from the interfaces to be used for the bridge. → Network →Network Configuration in the corresponding interface → Tab Zones. Remove the zones by clicking on . In the example »dmz1 »firewall-dmz1 »dmz1_v6 »interface-dmz1_v6}
Then Save
Under no circumstances may the zone be removed which is used for the current access !

Anschließend Speichern

Initial position Interfaces
Initial position Interfaces
Prepared interfaces
Prepared interfaces

Create a Bridge

In the example, the interfaces eth2 and eth3 are to be combined to a DMZ.
Start the wizard in the menu → Network →Network Configuration → Tab Network interfaces → Button Bridge

Caption Value Function

Step 1

Step 1
Name bridge0 Name of the bridge interface UTM v11.8.7 Netzwerk Schnittstellen Bridge-1-en.png
IP address: Example-IP address of the bridge interface
Activate STP: Off In addition, the Spanning Tree Protocol can be activated.

Step 2

Step 2
interfaces: »eth2 »eth3 Interfaces that are to be combined. Available interfaces can be selected in the click box. UTM v11.8.7 Netzwerk Schnittstellen Bridge-2-en.png

Step 3

Step 3
zones: »dmz1 »firewall-dmz1 »dmz1_v6 »firewall-dmz1_v6 Zones that are to be linked with the bridge interface.
In our example dmz1 and firewall-dmz1.
UTM v11.8.7 Netzwerk Schnittstellen Bridge-3.png
Add new zone: Off dmz2 If activated Ein, a new zone can be added to the bridge alternatively or additionally.
Generate Rules Off Port filter rules are automatically created for the new zone.
These rules first allow any network traffic (any rules) and must be replaced unconditionally by customized rules!

Configured bridge

Finish with Finish

Configured bridge

Customize network objects

UTM v11.8.7 Firewall Portfilter Netzwerkobjekte Bridge-en.png

AAfter setting up the interface, the network objects whose zones have been assigned to the bridge must be adapted. The bridge must be entered there as the interface.

Menu → Firewall →Port Filter → Tab Network objects → Button for each network object belonging to the bridge.

Change Interface to bridge0

This step can be skipped for automatically created zones:
  • Two new network objects are created for each of these zones:
  • The network objects are each linked to a zone:
    • zone-interface with the zone firewall-zone and
    • zone-network with the zone zone
  • The network objects are assigned to the interface bridge-name.

Orphaned network objects whose zones are no longer assigned to an independent interface should be removed.

Set up port filter rule

A port filter rule is required to allow network traffic between the interfaces belonging to the bridge.
A new network object is created for this purpose.
Name any UTM v11.8.7 Firewall Portfilter Netzwerkobjekte Bridge2-en.png
Type: Network (address)
Address: Any network traffic should be possible.
Zone: dmz1 Zone linked to the bridge.

Port filter rule for the bridge

Finally, only the port filter rule with the network object just created has to be created.
At this point a any-rule may actually be used so that the interfaces can communicate completely with each other.

╭╴ Action ╶╮ Accept
╭╴ Source ╶╮ all-dmz
╭╴ Destination ╶╮ all-dmz
╭╴ Service ╶╮ any
╭╴[–] Nat╶╮ ╭╴ Type ╶╮ None

Network traffic to other networks (internal or external) should then be restricted by rules that work with the network objects that are mapped to the bridge zone.

Example rule to release only ftp services from the DMZ
╭╴ Action ╶╮ Accept
╭╴ Source ╶╮ dmz1-network
╭╴ Destination ╶╮ Internet
╭╴ Service ╶╮ ftp
╭╴[–] Nat╶╮ ╭╴ Type ╶╮ Hidenat

The bridge setup is completed with Add and close Update rules.