We were having odd LAN issues and noticed we a had a bunch of these logs regarding ports on a WS-X6904-40G card.

%CONST_DIAG-3-HM_PORT_TEST_FAIL: Module 2 TestUnusedPortLoopback Port(s)[12] failed. System operation continues.
%HA_EM-6-LOG: Mandatory.go_nondislp.tcl: GOLD EEM TCL policy for TestNonDisruptiveLoopback

The module showed there was a minor error – however all ports remained up. We did see that spanning tree interface details were flapping between “P2P” and “Dispute” for the first 8 interfaces. Shutting these ports and letting traffic flow via secondary links restored normal functionality until we could swap the card. So it seems that despite issues with the ports being detected, the system was not err-disabling them.

Given the issue was across two different 4 port modules I assume the issue was with whatever hardware was driving the first 8 ports. All MAC and ARP entries looked fine but obviously weren’t timing out given the issue was intermittent.

show module snippet:

Mod  Online Diag Status
---- -------------------
  1  Pass
  2  Minor Error
  3  Pass
  4  Pass