FS-424D → FS-424E Core Replacement (FortiLink + MC-LAG) – Migration Sequence

Forum|Forum|5 months ago
March 27, 2026
3 replies
298 views

Hello TAC,

We are replacing 2 × FS-424D core switches (FortiLink-managed, configured as an MC-LAG pair with ICL) with 2 × FS-424E.

When we attempted to replace the first switch, all downstream switches and APs went offline.

Can you confirm the correct replacement sequence for this scenario, and whether the new 424E switches must be pre-configured before connection or if they will automatically inherit configuration from FortiLink after joining the fabric?

Thanks.

FortiSwitch

Best answer by SKIBBIDI

TAC provided a much simpler solution

Fortiswitch FS-424E will not inherit the new configs. The correct way of replacing your switches with a switch of a different model is as below:

1. Disconnect existing core switches. [Do not delete the switches, as we can refer to configs later]/

2. Connect new switches without any pre-configurations, enable MCLAG-ICL between the switches.

3. Once you've confirmed switches are online, configure the new switches from Fortigate cli or GUI. [Refer to old switches configs as they are still stored on the FGT]

4. After completing the configs and testing, old switches can now be deleted.

AEK

SuperUser

Hi Skibi

Try follow this guide.

https://docs.fortinet.com/document/fortiswitch/7.6.5/fortilink-guide/173284/replacing-a-managed-fortiswitch-unit

Also make sure the versions are compatible (recommended "R" is better).

https://fortinetweb.s3.amazonaws.com/docs.fortinet.com/v2/attachments/d756e8a9-6d2d-11e9-81a4-00505692583a/FortiLinkCompatibility.pdf

Hope it helps.

AEK

SKIBBIDIAuthorAnswer

New Member

TAC provided a much simpler solution

Fortiswitch FS-424E will not inherit the new configs. The correct way of replacing your switches with a switch of a different model is as below:

1. Disconnect existing core switches. [Do not delete the switches, as we can refer to configs later]/

2. Connect new switches without any pre-configurations, enable MCLAG-ICL between the switches.

3. Once you've confirmed switches are online, configure the new switches from Fortigate cli or GUI. [Refer to old switches configs as they are still stored on the FGT]

4. After completing the configs and testing, old switches can now be deleted.