MikroTik – RouterOSv7 first look – MLAG on CRS 3xx switches

What is MLAG?

Multi-Chassis Link Aggregation Group or MLAG is an idea that’s been around for a while.

It allows for the ability to form LACP channels across multiple physical switches.

Wikipedia shows a few different topology examples here


Vendor implementations are proprietary but the idea of MLAG was first mentioned in 802.1AX-2008 in 2008.

It first started to become popular in data center networking in the late 2000s

What makes the addition of MLAG to MikroTik’s RouterOS feature set notable is that it lowers the barrier to entry for this particular feature.

CRS 3xx switches are very inexpensive (starting at $149 USD) and may very well be the lowest cost MLAG capable hardware available on the market.

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Introduced in 7.1beta6

MLAG has been asked for by the MikroTik community a number of times and the most active feature request thread started here in 2020:

new feature request MLAG!!! – MikroTik

MikroTik added several version 7 beta releases in 2021 and included MLAG for all CRS 3xx series switches in 7.1beta6 on May 18th, 2021.

Overview of protocol requirements

MLAG is fairly consistent across vendors with the need for a link between physical devices that manages the MLAG groups. In MikroTik, these are called peer ports which facilitate the ICCP.

Here are a few terms for MikroTik MLAG:

ICCP (Inter Chassis Control Protocol). – Responsible for determining active/secondary switches and maintaining and updating the bridge table between physical switches.

Peer port – An interface that will be used as a peer port. Both peer devices use inter-chassis communication over the peer ports to establish MLAG and update the host table. The Peer port should be isolated on a different untagged VLAN using a pvid setting. The Peer port can be configured as a bonding interface.

System-id – The lowest MAC address between both peer bridges will be used as the system-id. This system-id is used for (R)STP bridge identifier.

Active-role – The peer with the lowest bridge MAC address will be acting as a primary device. The primary device is responsible for sending the correct LACP system ID on all MLAG ports.

mlag-id – An integer from 0 to 4294967295, it is used to set the MLAG ID for bonding interfaces. The same MLAG ID should be used on both peer devices to successfully create a single MLAG.

MikroTik’s requirements for ICCP and MLAG are:

  • RouterOS ICCP does not require an IP configuration
  • It should be isolated from the rest of the network using a dedicated untagged VLAN
  • Peer ports can also be configured as LACP bonding interfaces
  • MLAG requires enabled STP or RSTP protocol.


In order to present a single MAC address for the L2 spanning tree topology, ICCP functions on top of the peer ports to manage the MLAG/LACP system-id.

The system-id is used as the MAC address presented to the LACP client for RSTP/MSTP bridge identification.

reference for images and MLAG definitions: Multi-chassis Link Aggregation Group – RouterOS – MikroTik Documentation


Lab Example

In order to test the new MLAG functionality, we decided to setup a lab with CRS326-24S+2Q switches and CCR2004-1G-12S+2XS routers.

Below is the lab physical and logical topology.

Configuring an MLAG Group

Configure Bond and MLAG ID on CSW-01

/interface bonding
add mlag-id=100 mode=802.3ad name=Po1 slaves=sfp-sfpplus1


Configure Bond and MLAG ID on CSW-02

/interface bonding
add mlag-id=100 mode=802.3ad name=Po1 slaves=sfp-sfpplus1


* Apply each configuration step below on both switches to complete mlag setup and mlag-id 100. *


Configure the bridge and enable VLAN filtering. Add MLAG bonded interfaces and peer port to the bridge.

/interface bridge
add name=Bridge-MLAG vlan-filtering=yes
/interface bridge port
add bridge=Bridge-MLAG interface=Po1
add bridge=Bridge-MLAG interface=qsfpplus1-1 pvid=777


Configure a VLAN to be used over the MLAG

/interface bridge vlan
add bridge=Bridge-MLAG tagged=Po1 vlan-ids=3000


Set the peer port

/interface bridge mlag
set bridge=Bridge-MLAG peer-port=qsfpplus1-1


Validate the MLAG group


Show the status of the MLAG group, active and secondary ports and verify the system-id the client LACP receives

######## MLAG Switches - 2 x CRS326 ############

[[email protected]] > interface/bridge/mlag/monitor 
       status: connected
    system-id: 48:8F:5A:3A:44:BA
  active-role: primary

[[email protected]] > interface/bridge/mlag/monitor                        
       status: connected
    system-id: 48:8F:5A:3A:44:BA
  active-role: secondary

######## NON-MLAG LACP Router ############

[[email protected]] > /interface bonding monitor Po1
                    mode: 802.3ad
            active-ports: sfp-sfpplus3,sfp-sfpplus4
          inactive-ports: 
          lacp-system-id: 48:8F:5A:00:4F:80
    lacp-system-priority: 65535
  lacp-partner-system-id: 48:8F:5A:3A:44:BA


Configurations

RTR-01

/interface bridge
add name=Lo0
/interface bonding
add mode=802.3ad name=Po1 slaves=sfp-sfpplus3,sfp-sfpplus4 transmit-hash-policy=layer-2-and-3
/interface vlan
add interface=Po1 name=vlan3000 vlan-id=3000
/routing table
add fib name=""
/ip address
add address=100.126.0.1/29 interface=vlan3000 network=100.126.0.0
add address=100.127.0.1 interface=Lo0 network=100.127.0.1
/ipv6 address
add address=200:100:126::1 interface=vlan3000
add address=200:100:127::1/128 advertise=no interface=Lo0
/system identity
set name=RTR-01

RTR-02

/interface bridge
add name=Lo0
/interface bonding
add mode=802.3ad name=Po1 slaves=sfp-sfpplus3,sfp-sfpplus4 transmit-hash-policy=layer-2-and-3
/interface vlan
add interface=Po1 name=vlan3000 vlan-id=3000
/routing table
add fib name=""
/ip address
add address=100.126.0.2/29 interface=vlan3000 network=100.126.0.0
add address=100.127.0.2 interface=Lo0 network=100.127.0.2
/ipv6 address
add address=200:100:126::2 interface=vlan3000
add address=200:100:127::2/128 advertise=no interface=Lo0
/system identity
set name=RTR-02

CSW-01

/interface bridge
add name=Bridge-MLAG vlan-filtering=yes
/interface bonding
add mlag-id=100 mode=802.3ad name=Po1 slaves=sfp-sfpplus1
add mlag-id=101 mode=802.3ad name=Po2 slaves=sfp-sfpplus2
/interface bridge mlag
set bridge=Bridge-MLAG peer-port=qsfpplus1-1
/interface bridge port
add bridge=Bridge-MLAG interface=Po1
add bridge=Bridge-MLAG interface=qsfpplus1-1 pvid=777
add bridge=Bridge-MLAG interface=Po2
/interface bridge vlan
add bridge=Bridge-MLAG tagged=Po1,Po2 vlan-ids=3000
/system identity
set name=CSW-01

CSW-02

/interface bridge
add name=Bridge-MLAG vlan-filtering=yes
/interface bonding
add mlag-id=100 mode=802.3ad name=Po1 slaves=sfp-sfpplus1
add mlag-id=101 mode=802.3ad name=Po2 slaves=sfp-sfpplus2
/interface bridge mlag
set bridge=Bridge-MLAG peer-port=qsfpplus1-1
/interface bridge port
add bridge=Bridge-MLAG interface=Po1
add bridge=Bridge-MLAG interface=qsfpplus1-1 pvid=777
add bridge=Bridge-MLAG interface=Po2
/interface bridge vlan
add bridge=Bridge-MLAG tagged=Po1,Po2 vlan-ids=3000
/system identity
set name=CSW-02

7 thoughts to “MikroTik – RouterOSv7 first look – MLAG on CRS 3xx switches”

  1. Muito interessante, a Mikrotik terá que verificar muitos pontos para voltar a concorrência com os maiores players do mercado em especial Huawei, que tomou muito mercado da Mikrotik, principalmente nos pequenos provedores de internet.

  2. In a MLAG+MALG setting: can the peer ports of the second stage be a MLAG through the first stage?

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