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Short summary, RouterOS implementation of an IEEE 802.1BR standard, description of a Controller Bridge and Port Extender, description of a cascade, control (and upstream), extended ports (image), table of supported devices and features.

Controller Bridge (CB) and Port Extender (PE) is an IEEE 802.1BR standard implementation in RouterOS for CRS3xx series switches. It allows virtually extending the CB ports with a PE device and manage these extended interfaces from a single controlling device. Such configuration provides a simplified network topology, increased port density and manageability. A Controller Bridge and Port Extender topology can be seen below.

The Controller Bridge establishes communication with the Port Extender through a cascade port. Similarly, the Port Extender will communicate with the Controller Bridge only through an upstream port. On a PE device, there can be multiple control ports configured, but only one port (closest to the CB) will act as an upstream port. Cascade and upstream ports are used to transmit and receive control and network traffic. Extended ports are interfaces that are controlled by the CB device and they are typically connected to the end hosts. Extended ports only transmit and receive network traffic.

See supported features for each switch model below.

ModelController BridgePort Extender
netPower 15FR (CRS318-1Fi-15Fr-2S)-+
netPower 16P (CRS318-16P-2S+)-+
CRS326-24G-2S+ (RM/IN)-+

Quick setup

In this example, we will create a Controlling Bridge (e.g. a CRS317-1G-16S+ switch) that will connect to a single Port Extender (e.g. a CRS326-24G-2S+ switch) through an SFP+1 interface.

First, configure a bridge with enabled VLAN filtering on a CB device:

/interface bridge
add name=bridge1 vlan-filtering=yes

On the same device, configure a port that is connected to the PE device and will act as cascade port:

/interface bridge port-controller
set bridge=bridge1 cascade-ports=sfp-sfpplus1 switch=switch1

Last, on a PE device, simply configure a control port, which will be selected as an upstream port:

/interface bridge port-extender
set control-ports=sfp-sfpplus1 switch=switch1

Once PE and CB devices are connected, all interfaces (excluding control ports) that are on the same switch group will be extended and can be further configured on a CB device.

In order to exclude some port from being extended (e.g. for out-of-band management purposes), additionally, configure excluded-ports property.

Packet flow and forwarding

ETAG usage, packet flooding (broadcast, multicast, unicast), unicast forwarding, learning.

Controller Bridge settings

List of available configuration properties, monitoring options. Neighbor discovery changes (how PE and CB discover each other using LLDP TLVs, on PE control-ports discovery is automatically enabled and disabled on extended ports (they get controlled by the CB settings), on CB cascade ports discovery is automatically enabled), automatic bridge port configuration, how to apply and remove (device remove, port remove, other settings where an extended interface is configured will stay and should be removed manually) the configuration for extender ports (PE can even be disconnected and still apply configuration on CB), extended port naming, ECP protocol for control information between PE and CB.

Port Extender settings

Similar as CB


Known limitation (e.g. only single CB possible, ingress-filtering on extended ports) and recommendations (e.g use control/cascade ports only for communication between CB and PE, do not use these ports for bridging or routing)


Some most basic and commonly used examples

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