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Multi-Chassis Link Aggregation (MLAG) technology enables a pair of network switches to connect to one another and appear as a single logical switch (known as a link aggregation group, or LAG). MLAG is a way to get around the limitations of Spanning Tree Protocol (STP). With STP, networks may be configured with redundant links between switches, but only one link is active at any given time. That effectively means 50% of network bandwidth goes unused at all times. With MLAG, a switch may connect to a pair of MLAG-connected switches (the LAG) via redundant links that are both active. There’s no need to block certain links, as with STP, resulting in improved bandwidth utilization and performance. MLAG peer switches synchronize forwarding state between them, so if a switch fails, traffic is automatically rerouted for continuous uptime. It is supported by the Pica8 PICOS network operating system when used with PicaPilot.

This document describes how to configure MLAG in PICOS. 


  • The configurations at both ends of the MLAG peer-link must be consistent, including Native vlan-id, Untagged vlan-id, Tagged vlan-id, Mac learning, and System ID.
  • From PICOS 2.11.7, MLAG supports IGMP snooping.
  • If you want to correctly implement IGMP snooping with MLAG, either enable or disable IGMP snooping on both MLAG peers.
  • If IGMP snooping is implemented to the MLAG network, the static Layer 2 multicast entries (including both member port and router port entries) cannot be synchronized to the MLAG peer.
  • MLAG does not support DHCP relay.


Step1         Configure an aggregation interface with LACP mode.

    set interface aggregate-ethernet <lag_name> aggregated-ether-options lacp enable <true | false>

Step2         Enable MLAG on a LAG.

                   set interface aggregate-ethernet <lag_name> aggregated-ether-options mlag disable <true | false>

                   By default the MLAG function is enabled.

Step3         Configure MLAG domain ID.

                   set interface aggregate-ethernet <lag_name> aggregated-ether-options mlag domain-id <domain-id>

Step4         Add member interfaces to a LAG.

                   set interface gigabit-ethernet <port> ether-options 802.3ad <lag_name>

Step5         Configure an aggregation interface to VLAN members.

                   a)      Configure VLAN ID.

    set vlans <vlan-id>

    b)     Configure the interface to VLAN.

    set interface gigabit-ethernet <port> family ethernet-switching native-vlan-id <vlan-id>

    set interface aggregate-ethernet <lag_name> family ethernet-switching port-mode <port-mode>

                   set interface aggregate-ethernet <lag_name> family ethernet-switching vlan members <vlan-id>

Step6         Configure the L3 interface IP address.

                   set vlan-interface interface <interface-name> vif <vif-name> address <address> prefix-length <number>

Step7         Configure the peer IP address and the peer-link for the MLAG peer.

                   set interface aggregate-ethernet <lag_name> aggregated-ether-options mlag peer <ipv4_address> peer-link <text>

Step8         Configure a static ARP entry for peer-link interface.

   a)      Configure a static MAC entry to create a hardware forwarding entry, where the interface is the outbound physical interface or LAG interface.

   set interface gigabit-ethernet <interface-name> static-ethernet-switching mac-address <mac-addrvlan <vlan-id>

   b)     Configure a static ARP entry for peer-link interface.  

   set protocols arp interface <interface> address <ipv4-addr> mac-address <mac-addr>


PICA8 recommends configuring a static ARP for peer-link interface to prevent ARP entry of the peer-link interface from being modified by ARP attack packets.

Step9         (Optional) Configure MLAG system priority.

           set interface aggregate-ethernet <lag_name> aggregated-ether-options mlag priority <value>

Step10        (Optional) Configure hello interval timer.

   set interface aggregate-ethernet <lag_name> aggregated-ether-options mlag hello-interval <value>

Step11      (Optional) Configure reload delay timer.

           set interface aggregate-ethernet <lag_name> aggregated-ether-options mlag reload-delay <value>

Step12      (Optional) Configure system ID for LACP.

           set interface aggregate-ethernet <lag_name> aggregated-ether-options mlag system id <macaddr>

   System ID configured on the MLAG peer devices should be consistent.

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