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New Member

Port fails POST in loopback test

Hi,

I have a Cisco CBS3020-HPQ chassis switch running IOS 12.2.(25r)SEF3.  One of the ports is in "disabled" state but when I try to unshut it, it doesn't work, the switch logs shows the following event:

%PLATFORM_ENV-3-LOOPBACK_PORT_POST_ERR: Gi0/1 can't be brought up because it failed POST in Loopback test

I'm not sure why this is happening, does anyone know what might cause this and how do I resolve this, the port is unusable since I can not get it out "disabled" state.

Any replies would be appreciated.

Thanks,

Sayed

Everyone's tags (4)
8 REPLIES
VIP Super Bronze

Port fails POST in loopback test

Hi Sayed,

It appears that that particular port has failed the testing that is usually done on all ports during the switch start up.  If you can turn it off and Waite a few minutes than turn it back on.  If the problem persist, you may have to open a ticket with TAC and RMA the switch

HTH

Hall of Fame Super Gold

Port fails POST in loopback test

There's nothing you can do but contact Cisco TAC and arrange for an RMA.  Your blade is about to have a ASIC failure.

New Member

Re: Port fails POST in loopback test

leolaohoo:

You appear to have some experiencial knowledge of these issues. How much $$$ is an RMA likely to cost?

In my WS-C3560-48PS-S *V04, I have only Fa 0/7 and Fa 0/8 associated with this failure indication:

%PLATFORM_ENV-3-LOOPBACK_PORT_POST_ERR: Fa0/7 can't be brought up because it failed POST in Loopback test.

%PLATFORM_ENV-3-LOOPBACK_PORT_POST_ERR: Fa0/8 can't be brought up because it failed POST in Loopback test.

Are you saying this type of failure is likely to cascade through the entire ASIC for the group of ports this ASIC serves? Or is the failure static to just the currently affected ports?

Even if the entire ASIC for a group of ports fails, depending on how many ports the switch has, there might be several groups of ports which continue to function normally. Is this not correct?

Or are you saying that the entire switch will eventually become a boat anchor?

I am an electrical engineer by training, and a fair electronics hobbyist, but I'm not up to floating a new ASIC upon the system board, nor do I have the proper clean room.

But I will certainly make good use of the other 46 FastEthernet ports while I can.

Now if I can just determine if the lack of PoE on all ports is related to this Fa 0/7&8 problem.

Hall of Fame Super Gold

Port fails POST in loopback test

You appear to have some experiencial knowledge of these issues. How much $$$ is an RMA likely to cost?

IF you have a valid Cisco Service Contract then you could get the hardware replaced for no extra cost.  If you don't then you can talk to the dealer who sold you the kit and maybe you can work something out.

Otherwise, you may consider looking at Cisco Refurbished if you need used appliance.

Are you saying this type of failure is likely to cascade through the entire ASIC for the group of ports this ASIC serves? Or is the failure static to just the currently affected ports?

Can't say.  I've seen these error messages before and what happens next is a hit-and-miss.  Sometimes I slam the flat side of the switch against the floor several times and all go good.  Most of the times ASIC failure cascade to the next.  The problem when it comes to the PoE controller is what happens if it starts to burn something.  Particularly if you have a business and it happens at night.  These are risks I'm unwilling to take.

New Member

Port fails POST in loopback test

Hi, I can't agree this this problem not observed in WS-C3750X with 12.2 (53)SE2, please look for it:

: %PLATFORM_ENV-3-LOOPBACK_PORT_POST_ERR: Gi1/0/25 can't be brought up because it failed POST in Loopback test.

New Member

Port fails POST in loopback test

It is a bug of the IOS. Check this bug CSCti75491 details.

Symptom:


C3750x and C3560x switches may fail the POST port loopback test on some ports when booting with the error %PLATFORM_ENV-3-LOOPBACK_PORT_POST_ERR: Gi1/0/X can't be brought up because it failed POST in Loopback test.


Conditions:


The c3750x and c3560x switches may see this issue when running IOS 12.2(53)SE2. A shut/no shut will not clear the issue.


Workaround:


1) Upgrade to IOS 12.2(55)SE. The problem is not observed in this image.

2) Skip POST when booting from the switch: prompt.

switch: boot -skip_post flash:


New Member

Port fails POST in loopback test

Ahh,

I just upgraded to IOS 12.2.(55)se6 and I have had the same experience.

I have 4 ports that cannot be brought up and I've used this firmware on several of my 3560 switches.

I'm wondering if I should upgrade to 12.2(55) se8.

/Nick

Hall of Fame Super Gold

Port fails POST in loopback test

Post the output to the command "sh post".

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