[c-nsp] %ETHCNTR-3-LOOP_BACK_DETECTED on cisco 3550

[Keith.Crow at SEMATECH.Org]

    I saw that Brett on March 31 had this same problem. I was wondering
what he did to resolve this issue. My 3550 has been running for 2 years
and just started this problem.

Thanks Keith



strange problem on 3550G and 2950G switches: 3550 is attached via MM SX
GBIC to a 2950G (same GBIC). equipment burned in for a week, and has
slowly started exhibiting this problem on the fiber link between these
two switches: Loop-back detected o:18.751 MST:
%ETHCNTR-3-LOOP_BACK_DETECTED: Loop-back detected on
GigabitEthernet0/10. The port is forced to linkdown. 000068: *Feb 28
18:36:20.751 MST: %LINK-5-CHANGED: Interface GigabitEthernet0/10,
changed state to administ ratively down 000069: *Feb 28 18:36:21.751
MST: %LINEPROTO-5-UPDOWN: Line protocol on Interface
GigabitEthernet0/10, chan ged state to down the error message on
cisco.com states: Error Message ETHCNTR-3-LOOP_BACK_DETECTED:, Loop-back
detected on [chars]. The port is forced to linkdown. Explanation This
message means that the loop-back condition might be caused by a balun
cable being accidentally plugged into the port. [chars] is the port.
Recommended Action Check the cables. If a balun cable is connected and
the loopback condition is desired, no action is required. Otherwise,
connect the correct cable, and bring the port up by entering the no
shutdown interface configuration command. given that this is a fiber
connection (tried both 10 and 15ft. fiber patch cables), obviously the
cisco explanation doesn't fly. has anyone seen a similar problem? i've
swapped GBICs, fiber patch cables, moved the GBICs to different ports on
*both* switches, but the error message above *always* shows up on the
3550, and the 3550 shuts the link down. 3550 is running 12.1(12c) EA1
2950G is running 12.1(11) EA1 only thing i can think is a software bug
on the 3550 (other 2950 attached with same GBICs and fiber patches does
not exhibit this problem).