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3750x stack switch


I have a 3750X switch stack(2 switches) using them as Distribution switch.

Sw2 is the master and Sw1 is member.  From Distribution switch, we have multiple interfaces bundled as port-channel and uplink to the Core and access switches.


As soon as  both switches are powered on, we are starting to see this message. 

%SUPQ-4-CPUHB_SLOW_TRANSMIT: CPU Heartbeat Tx buffer not returned (switchname-1)

%SYS-3-CPUHOG: Task is running for (2312)msecs, more than (2000)msecs (682/129),process = Licensing Auto Update Process.

Also 1 or 2 times in an hour, it bounces all the active interfaces on Switch 1 for about 1 or 2 seconds.  it comes right back on though..

Switches run fine for 3-4 hours than we starts to seeing vlan flapping than after 1-3 hours later, t brings the whole network down.

%SW_MATM-4-MACFLAP_NOTIF: Host 001b.d510.aba8 in vlan 100 is flapping between port Po1 and port Po3

while we are seeing vlan flap messages, we see this as well.

%HLFM-3-SEND_FAIL: Failed to send RPC message, req 3,
-Traceback= 6C6788z 2EA60D4z 356FEB0z 3570730z 356D3CCz 356D520z 35659CCz 3561D4Cz

I power down the Switch 1 and everything works fine.

I created a TAC case but I can only work on this on a scheduled maintenance time.  Maybe in couple days.

Anyone experienced this issue before?  Any suggestion would appreciated.


5 Replies 5

Ich Nafi

Those 3750X's stacking cables have very sensitive connectors. I would check the cables first. Maybe there are damaged pins or corrosion.


I got the same error of "%SUPQ-4-CPUHB_SLOW_TRANSMIT: CPU Heartbeat Tx buffer not returned" on C3750ME. TAC case opened, but seems can't find the solution... I checked all cables, replaced the switch. The issue is still persistent...

Have you fix it? Could you share the solution if it's done?

Did you change the ios code when the switch changed ?

Error Message SUPQ-4-CPUHB_TX_FAIL:CPU Heartbeat TX Failed

Explanation This message means that the system is warning you about the transmit interface

discarding the heartbeat message.

Recommended Action Copy the error message exactly as it appears on the console or in the system log,

call your Cisco technical support representative, and provide the representative with the gathered



My switch was a Distribution switch.

I powered down the standby switch than problem went away.  When i brought the switch back on, we started seeing the issue.  I'd talked to TAC but did not help.

Here's what I did to fix the issue.   I took out the secondary switch from the stack and added it back.   Since than i've not seen the message.  

When you take a secondary switch out from the stack, be careful, you are going to loose configs for the second switch.  Just back it up and copy them back.

I hope this will help with your issue.  Good luck

Thanks for your reply. Actually, my problem is a bit different. I'm using 3750ME with trunking on Fast Ethernet interface. But I got the same error "%SUPQ-4-CPUHB_SLOW_TRANSMIT: CPU Heartbeat Tx buffer not returned". I tried to search on the internet, but no luck to solve it yet.

I did whatever I can... replaced the cables, RMA the switch ...etc. But the error is still persistent... So wanna to see I can have any hint at your issue.

Again, thanks for your experience sharing!!!

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