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Summary


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.

ModelController BridgePort Extender
netPower 15FR (CRS318-1Fi-15Fr-2S)-+
netPower 16P (CRS318-16P-2S+)-+
CRS326-24G-2S+ (RM/IN)-+
CRS328-24P-4S+-+
CRS328-4C-20S-4S+-+
CRS305-1G-4S+-+
CRS309-1G-8S+++
CRS317-1G-16S+++
CRS312-4C+8XG++
CRS326-24S+2Q+++
CRS354-48G-4S+2Q+++
CRS354-48P-4S+2Q+++

Limitations

Although controller allows to configure port extender interfaces, some bridging and switching features cannot be used or will not work properly. Below are the most common controller and extender limitations. The list might change with an upcoming RouterOS releases.

FeatureSupport
Bonding for cascade and upstream ports +
Bridge VLAN filtering+
Bonding for extended ports-
Dot1x authenticator (server)-
Ingress and egress rate-
Mirroring-
Port isolation-
Storm control-
Switch rules (ACL)-

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 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 excluded-ports property.


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.

Discovery and control protocols


Before frame forwarding on extended ports is possible, Controlling Bridge and Port Extender must discover each other and exchange with essential information.

CB and PE enabled devices are using a neighbor discovery protocol LLDP with specific Port Extension TLV. This allows CB and PE devices to advertise their support on cascade and control ports.

CB and PE configuration can override the neighbor discovery settings, for example, if a cascade port is not included in a neighbor discovery interface list, the LLDP messages will be still sent.

Once LLDP messages are exchanged between CB and PE, a Control and Status Protocol (CSP) over an Edge Control Protocol (ECP) will initiate. The CSP is used between CB and PE to assert control and receive status information from the associated PE - it assigns unique IDs for extended ports, controls data-path settings (e.g. port VLAN membership) and sends port status information (e.g. interface stats, PoE-out monitoring). The ECP provides a reliable and sequenced frame delivery (encoded with EtherType 0x8940).

The current CB implementation does not support any failover techniques. Once the CB device becomes unavailable, the PE devices will lose all the control and data forwarding rules.

Packet flow


To better understand the underlying principles of Controlling Bridge and Port Extender, a packet walkthrough is provided below:

  1. An L2 packet is received on the extended port; \\ 
  2. The Port Extender encapsulates the packet with an E-TAG header (EtherType 0x893F) and forwards it through an upstream port, towards the Controller Bridge. An E-TAG packet contains information regarding the PE source port ID. The PE device does not make any local switching decisions; \\ 
  3. The Controller Bridge receives the E-TAG packet and knows exactly which extended interface received it. The CB then internally decapsulates the packet and proceed it through a regular switching decision (host learning, destination address lookup, VLAN filtering, etc.);
  4. Once a switching decision is made, the CB will again encapsulate the original packet with an E-TAG and send it through a cascade port, towards Port Extender;
    1. For a single destination packet (unicast), the CB will include the PE destination port ID in the E-TAG and send it through a correct cascade port;
    2. For a multi-destination packet (broadcast, multicast or unknown-unicast), the CB will include a target group mark and source port ID in the E-TAG and send a single packet replica per every cascade port;
  5. Once a PE device receives an E-TAG packet on the upstream port, PE decapsulates it and sends the original L2 packet through the extended port;
    1. For a single destination packet (unicast), the PE will send the packet only to the correct extended port;
    2. For a multi-destination packet (broadcast, multicast or unknown-unicast), the PE will send a single packet replica per every extended port (except for the source port where the packet was received).

Controller Bridge settings and monitoring


This section describes the Controller Bridge settings and monitoring options. 

Sub-menu: /interface bridge port-controller

Property

Description

bridge (name; Default: none)The bridge interface where ports will be extended. The CB will only enable when bridge and switch properties are specified, otherwise, it will be in a disabled state.
cascade-ports (interfaces; Default: none)Interfaces that will act as cascade ports. A bonding interface with 802.3ad or balance-xor mode is also supported.
switch (name; Default: none)The switch that will act as the CB and ensure the control and network traffic. The CB will only enable when bridge and switch properties are specified, otherwise, it will be in a disabled state.

After CB and PE devices are configured and connected, each PE device will be automatically visible on the device menu, use print and monitor commands to see more details.

[admin@Controller] > interface bridge port-controller device print
Flags: I - inactive 
 0   name="pe1" pe-mac=64:D1:54:EB:AE:BC descr="MikroTik RouterOS 6.48beta35 (testing) CRS328-24P-4S+" control-ports=pe1-sfpplus1,pe1-sfpplus2 

 1   name="pe2" pe-mac=64:D1:54:C7:3A:58 descr="MikroTik RouterOS 6.48beta35 (testing) CRS326-24G-2S+" control-ports=pe2-sfpplus1
[admin@Controller] > interface bridge port-controller device monitor pe2
                 name: pe2
               status: active
  connected-via-ports: sfp-sfpplus1==pe1-sfpplus1,pe1-sfpplus2==pe2-sfpplus1
   connected-via-devs: controller,pe1

Sub-menu: /interface bridge port-controller device

Property

Description

connected-via-devs (name)Shows the connected devices in the path from PE to CB. 
connected-via-ports (name)Shows the connection path from PE to CB.
control-ports (interfaces)PE device control ports.
descr (name)Short PE device description.
name (name)Automatically assigned PE device name.
pe-mac (MAC address)PE device MAC address.
status (active | inactive)PE device status.

Additionally, each PE device interface can be monitored on the port menu, use print and monitor commands to see more details.

[admin@Controller] > interface bridge port-controller port print where !disabled
Flags: I - inactive, X - disabled, R - running, U - upstream-port, C - cascade-port 
 #    NAME                                   DEVICE
 0 I  pe1-ether1                             pe1
 1 R  pe1-ether2                             pe1
 2 R  pe1-ether3                             pe1
 3 R  pe1-ether4                             pe1
 4  U pe1-sfpplus1                           pe1
 5 RC pe1-sfpplus2                           pe1
 6 I  pe2-ether1                             pe2
 7 R  pe2-ether2                             pe2
 8 R  pe2-ether3                             pe2
 9 R  pe2-ether4                             pe2
10  U pe2-sfpplus1                           pe2
[admin@Controller] > interface bridge port-controller port monitor [find where !disabled]
           name: pe1-ether1 pe1-ether2 pe1-ether3 pe1-ether4 pe1-sfpplus1 pe1-sfpplus2 pe2-ether1 pe2-ether2 pe2-ether3 pe2-ether4 pe2-sfpplus1
         status: unknown    link-ok    link-ok    link-ok    no-link      link-ok      unknown    link-ok    link-ok    link-ok    no-link
           rate:            1Gbps      1Gbps      1Gbps      10Gbps       10Gbps                  1Gbps      1Gbps      1Gbps      10Gbps
    port-status: not-added  ok         ok         ok         ok           ok           not-added  ok         ok         ok         ok
           pcid:            457        458        459        480          481                     509        510        511        532

Sub-menu: /interface bridge port-controller port

Property

Description

device (name)Automatically assigned PE device name.
name (name)Automatically assigned PE port name.
pcid (integer)Automatically assigned port identifier.
port-status (dev-inactive | not-added | ok)PE port status.
rate (bps)Data rate of the connection.
status (link-ok | no-link | unknown)PE port link status.

The Controller Bridge can monitor the PoE-out related information from Port Extenders on the port poe menu, use print and monitor commands to see more details. For more information regarding PoE-out, please visit the PoE-out manual.

[admin@Controller] > interface bridge port-controller port poe print
 # NAME                                    DEVICE
 0 pe1-ether1                              pe1
 1 pe1-ether2                              pe1
 2 pe1-ether3                              pe1
 3 pe1-ether4                              pe1
 4 pe1-ether5                              pe1
 5 pe1-ether6                              pe1
 6 pe1-ether7                              pe1
...
[admin@Controller] > interface bridge port-controller port poe monitor pe1-ether2,pe1-ether3
               name: pe1-ether2 pe1-ether3
     poe-out-status: powered-on powered-on
    poe-out-voltage: 52.8V      52.9V
    poe-out-current: 123mA      95mA
      poe-out-power: 6.4W       5W

Port Extender settings


This section describes the Port Extender settings.

Sub-menu: /interface bridge port-extender

Property

Description

control-ports (interfaces; Default: none)Interfaces that will either connect to the CB (upstream port) or connect other PE devices in series (cascade port). A bonding interface with 802.3ad or balance-xor mode is also supported.
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. The PE will only enable when this property is specified, otherwise, it will be in a disabled state.

Configuration examples


Below are described the most common configuration examples. Some examples are using bridge VLAN filtering, so make sure to understand the filtering principles first - bridge VLAN filteringbridge VLAN table.

Basic CB and PE configuration


The basic CB and PE configuration examples 

/interface bridge
add name=bridge1 vlan-filtering=yes
/interface bridge port
add bridge=bridge1 interface=sfp-sfpplus2


Error rendering macro 'code': Invalid value specified for parameter '[Ljava.lang.Object;@3b4b7d3'
/interface bridge port-controller
set bridge=bridge1 cascade-ports=sfp-sfpplus1 switch=switch1


Error rendering macro 'code': Invalid value specified for parameter '[Ljava.lang.Object;@bbc8373'


Trunk and Access ports

Bonding for cascade and upstream ports

Configuration removal

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