Troubleshooting Tip: FortiLink Switch new peer detected logs on FortiGate Switch-Controller Event logs

Functionality Impact and Symptoms:

• 'New peer detected' messages appear in the FortiSwitch event log continuously on the FortiGate. For example:

date=2025-08-01 time=04:12:22 eventtime=1756871361886880822 tz="+0200" logid="0115032624" type="event" subtype="switch-controller" level="information" vd="root" logdesc="Fortilink Switch new peer detected" user="Switch-Controller" ui="fortilinkd" name="xxxxx" sn="xxxxx" msg="New peer (S148Fxxxxx) detected on port (port22)"

• FortiLink Topology Display Issue with MCLAG Aggregation Switches. Topology will not show solid inter-switch links. It may show no lines or dotted lines.

Trigger Condition: FortiLink setup with FortiSwitch firmware versions 7.6.2 or 7.4.7, and the total number of trunk members (FortiLink + Inter Switch Links + Inter Chassis Link) exceeds 5 on any switch.

User Impact: NA (A display issue occurs on the FortiGate; However, data traffic is not affected.)

The issue is fixed in FortiGate versions 7.4.9, 7.6.4, and above.

For a workaround, contact support for more details.

Workarounds:

• Downgrade the FortiSwitch firmware to versions 7.6.1 or 7.4.6.
• Or if it is feasible, reduce the total number of trunk member ports to 5 or fewer on the switch.
• Or change the FortiLink mgmt-mode to https on the affected switch.

Note: When switching to HTTPS mode:

• If the switch is a core switch and fortilink-neighbor-detect is set to 'LLDP', change detect mode to 'fortilink'.
• Before doing so, verify that the FortiLink trunk (FL) on the switch does not have the 'set static-isl enable' setting.
• After changing the neighbor detect mode to 'fortilink' on the FortiGate, ensure that the name of the FortiLink trunk on the switch does not include the '-0' suffix.
• Finally, enable 'set isl-static enable' in that FortiLink trunk (FL).