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When using the 1000-Base-T RJ45 copper SFP module, the port shows as 'up' or online even when there is no UTP (Unshielded Twisted Pair) cable connected to the Transceivers.
The 1000-Base-T RJ45 copper SFP module is a particular module which requires the use of 1000auto speed configuration.
Using other speed configs like 1000full or auto-module may cause the link to not come online or could cause the issue in the example below.
This example assumes the following setup:
- Laptop1 using port43 through FortiSwitch FSW1 (port47, 48 in LACP).
- FortiSwitch FSW2 using port43 to connect to Laptop2.
- Port47 and port48 are in LACP, using a 1000-Base-T copper SFP module. The default port speed setting is auto-module.
Upon disconnecting the RJ-45 cable either on FSW1 or FSW 2 on port47 or port48, the traffic between the laptops is lost for 20-30 seconds.
When the SFP module is disconnected, less than 2 seconds of drop are visible.
This occurs because, according to the switch, the mac layer port is still up when a cable is disconnected. Therefore, the LACP trunk relies on LACP protocol to detect when a member port is down instead of when a physical port is down, meaning the process takes longer.
Solution:
Change the speed on port47 and port48 on both switches to 1000auto.
Run the following command to do this:
# config switch physical-port
edit port#
set speed 1000auto
end
Note that auto-module is not auto-negotiation. 1000auto simply enables auto-negotiation.
Additionally, auto-module means disabling the auto-negotiation and auto-detect speed based on the module, meaning it will not negotiate speed with the remote side.
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