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, flexibility, increased port density and ease manageability. An example of 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, control ports must be configured and only one port (closest to the CB) will act as an upstream port, other control ports can act as a backup for upstream port or even cascade port for switches connected in series (e.g. Port Extender 2 and 3 in the image above). 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.
|Model||Controller Bridge||Port Extender|
|netPower 15FR (CRS318-1Fi-15Fr-2S)||-||+|
|netPower 16P (CRS318-16P-2S+)||-||+|
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:
On the same device, configure a port that is connected to the PE device and will act as cascade port:
Last, on a PE device, simply configure a control port, which will be selected as an upstream port:
Once PE and CB devices are connected, all interfaces that are on the same switch group (except for control ports) will be extended and can be further configured on a CB device. An automatic bridge port configuration will be applied on the CB device which adds all extended ports in a single bridge, this configuration can be modified afterward.
In order to exclude some port from being extended (e.g. for out-of-band management purposes), additionally, configure
Make sure not to include the cascade-ports and control-ports in any routing or bridging configurations. These ports are recommended only for a CB and PE usage.
ETAG usage, packet flooding (broadcast, multicast, unicast), unicast forwarding, learning.
/interface bridge port-controller
|bridge (name; Default: none)||The bridge interface where ports will be extended.|
|cascade-ports (interfaces; Default: none)||Interfaces that will act as cascade ports.|
|switch (name; Default: none)||The switch that will act as the controller and ensure the control and network traffic.|
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.
/interface bridge port-extender
|control-ports (interfaces; Default: none)||Interfaces that will either connect to the CB (an upstream port) or connect other PE devices in series (a cascade port).|
|excluded-ports (interfaces; Default: none)||Interfaces that will not be extended.|
|switch (name; Default: none)||The switch that will act as the extender and ensure the control and network traffic.|
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