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How to configure MLAG in Extreme switches

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TitleHow to configure MLAG in Extreme switches
This article provides step-by-step procedures to configure MLAG (single-tier) in Extreme switches for a topology below: 

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  • EXOS 12.5 and above. 
  • Summit and BlackDiamond series
Step 1: Create the inter-switch connection (ISC) VLAN for carrying the MLAG control traffic. 

The ISC VLAN is a user-created VLAN that only carries the MLAG traffic. No data traffic is allowed to flow through this VLAN. 
create vlan <vlan name>
configure vlan <vlan name> tag <vlan id>
configure vlan <vlan name> add ports <port used to connect the MLAG peers> tagged
configure vlan <vlan name> ipaddress <xx.xx.xx.xx/30>
This VLAN should be created on both MLAG peers. It is recommended to use /30 IP address (one host address to each peer) so that IP subnet can be preserved and we can be sure that there is no other VLAN that could send the data traffic into this VLAN. 
It is strongly recommended that the ISC be configured on a LAG between both peers.

Step 2: Create and configure the MLAG peer.
create mlag peer <peer name>
configure mlag peer <peer name> ipaddress  <IP address of the ISC VLAN configured on the peer>
An MLAG peer should be created on both MLAG peers, pointing the IP addresses to each other. 
If the MLAG ports are using LACP, configure the LACP mac address used so this will always be the same.

configure mlag peer <peer name> lacp-mac <mac>

Step 3: Enable the MLAG port on both peers.

Please also note if the downstream device (e.g. switch, server, etc..) is using LACP LAG sharing on its ports, it will be necessary to enable LACP LAG on the MLAG ports. This has to be done prior to enabling the port for MLAG
enable sharing port <port> grouping <port> algorithm addressed-based [ L2 | L3 | L3_L4 ] lacp

(the algorithm needs to match the downstream device)
enable mlag port <port number connected to the server/switch> peer <peer name> id <id value>

MLAG port should be enabled on both peers. The ID value used in the command should be unique for each MLAG instance but should be same on both the MLAG peers. For instance, if you are connecting another server in a similar fashion to the same MLAG peers on different ports, the ID value should change for this instance but should be same on both the MLAG peers. 

Step 4: Configure sharing/teaming on the switch/server connected to the MLAG peers. 

The ports connecting to the MLAG peers should be a part of a LAG group if it is a switch, or the NICs should be a part of the teaming if it is a server. 

Step 5: Add data carrying VLANs.

MLAG would take care of avoiding the loop in this topology with its ISC blocking mechanism.
The data carrying VLANs that are added in the uplink port of the downstream switch should be added on both the MLAG ports and the ISC ports of the peer switches.
If not added, in case of an MLAG port failure in one of the peer switch, the traffic of the downstream switch will not be forwarded to the other peer.

Note that there should not be a separate physical link for the data VLANs and the ISC VLAN. If configured this way, MLAG blocking filters will not be installed and a loop will be present.
Additional notes
MLAG concepts and configuration examples are provided in the EXOS user guide
You can also configure MLAG with Chalet on ExtremeXOS 21.1 and later.
It is recommended that the MLAG peers are of the same HW model and are running the same EXOS image. 
Only one ISC is allowed between two peers.

For more details about the MLAG functioning, please click Explaining Two-tier MLAG design

If using LACP, the MLAG peers must be running at least 15.3 to support MLAG with LACP.

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Sample configuration for the physical topology above:

Left MLAG peer switch:
create vlan isc
configure vlan isc tag 10
configure vlan isc add ports 1 tagged
configure vlan isc ipaddress
create mlag peer right 
configure mlag peer right ipaddress
enable mlag port 2 peer right id 100

Right MLAG peer switch: 
create vlan isc
configure vlan isc tag 10
configure vlan isc add ports 1 tagged
configure vlan isc ipaddress
create mlag peer left
configure mlag peer left ipaddress
enable mlag port 2 peer left id 100

The MLAG ISC can be created on a different VR if needed so the ISC vlan is not reachable by other devices on the switch. MLAG can switch vlans from multiple virtual-routers.

For more information on creating LAGs in EXOS:
How to create or delete a share group (LAG) in EXOS



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