Why can't I clear dynamic mac-addresses on my WS-C3750G-24TS switch?

[rweir0001]

Hi,

I want to clear some dynamic mac-addresses from a particular interface, and will settle for clearing all dynamic mac addresses, but my switch won't let me. We have a WS-C3750G-24TS running v12.2, and although it accepts the clear commands, it doesn't actually clear out the dynamic mac-addresses. Has anyone heard of this? Is it a bug? can anyone think of a way for me to clear these things out?

I've tried all of these commands, and the switch accepts them, but doesn't actually clear them:

clear mac address-table dynamic address xxxx.xxxx.d162 interface gi2/0/14

clear mac address-table dynamic address xxxx.xxxx.d162

clear mac address-table dynamic 

clear arp

[InayathUlla Sharieff]

Hi,

This is weird.  But try this and see if this works :-

int g2/0/14

shut

clear mac address

and check now show mac address int g2/0/14-- the mac should go.

HTH

Regards

Inayath

[rweir0001]

Thanks for the suggestion Inayath but "clear" is not a command option in config-if mode, only in privileged mode. I did try shutting the interface and then going back to privileged mode to clear the mac addresses but it did not solve the problem.

[devils_advocate]

Just tried #clear mac address-table dynamic on a 3750 in our test lab and it worked fine, it cleared all MAC addresses.

I would try an IOS upgrade next.

Have you got another 3750 on a different IOS which you can use as a test?

[rweir0001]

I don't think we have a spare but I'll check. I'm trying to schedule a time when I can reload the switch to see if that helps. It has been up for 26 weeks. The two ports I'm having issues with are connected to an ESXi host, and we were originally having problems with mac addresses flapping between ports. That was due to a load balancing issue on the vSwitch which has been fixed. We are still getting one last mac address flapping between ports. The mac is for an inactive vmnic card which also is the only vmnic with a dynamic mac address configured on a port on the 3750 switch. I think the 3750 is just having a mental health moment and hope a reload will correct it. If not then I may just upgrade the IOS.

[Madhukrishnan Gopinathan Nair]

Do you see the age of these mac ? is it getting refreshed after clearing?

May be you are receiving continuous traffic and ports keeps relearning it immediately.

Thanks,

Madhu

[rweir0001]

What command do I use to see the age of the dynamic mac address? I ran the sho mac address-table dynamic aging-time command but it just shows me the aging time for the VLAN that the mac is in , which is 300 seconds. I don't see a command to see the aging time of specific mac addresses.

I can see the aging time for the arp table, and that does clear when I run the clear arp command. In that instance, the same mac address I'm trying to clear keeps on showing that it is linked to a particular IP address. 

[Madhukrishnan Gopinathan Nair]

sh mac address-table dynamic
Legend: * - primary entry
        age - seconds since last seen
        n/a - not available

  vlan   mac address     type    learn     age              ports
------+----------------+--------+-----+----------+--------------------------
    10  68ef.bd10.3e94   dynamic  Yes          0   Po100
    10  68ef.bd10.3e96   dynamic  Yes          0   Po100
    20  0000.0c07.ac14   dynamic  Yes          0   Po100
   201  0026.9809.7dc1   dynamic  Yes          0   Po100

Thanks,

Madhu

[rweir0001]

Unfortunately, I do not have the age category in my output. Is there another way to determine the age?

DR-CORE#sh mac address-table dynamic
          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
  10    xxxx.xxxx.d758    DYNAMIC     Gi2/0/25
  10    xxxx.xxxx.0008    DYNAMIC     Gi1/0/25
  10    xxxx.xxxx.10e7    DYNAMIC     Gi2/0/25

[Madhukrishnan Gopinathan Nair]

I don't know. However I see that you have already shut the port and cleared the mac. If you still see it on the port (keeping the port shut), then it seems some issue. May be if possible, try a reload of the box.

Thanks,

Madhu

[rweir0001]

Thanks, Madhukrishnan. The dynamic mac address does remain on the port even with it shut and the clear command executed. I'll let you know how it works out after I reload the switch.

[Madhukrishnan Gopinathan Nair]

You are welcome and keep us posted. Also kindly do not forget  to rate any useful posts.

Thanks,

Madhu.

[InayathUlla Sharieff]

Okay,

Lets try this:-

1- I hope we dont have dual NIC connectivity and only one NIC to the Cat 3570 switch.

If the above statement is true:-

Go to the interface and shut down the interface and do not enable it.

Clear the mac address on that interface and run the command and check if you are able to see the mac address to appear after you clear.(When you clear the manual and you dont hav ethe link active it should flush out immediately).

2- In case this doesn work then is there any posibility to reboot the box?

HTH

Regards

Inayath

[rweir0001]

Thanks for the suggestions but the dynamic mac address is still assigned to the port even after I shut the port and clear the dynamic mac address. I'm going to reload the switch at some point soon. I'll post my results.

[Molody]

Hi! Here from 2024.

I Solved this issue in a cisco switch 2960, just reloading the switch with the command "reload". Be sure to save your configuration with the command "write memory".

Anyways, still can't find a way to delete the dynamically configurated MAC's with a "Clear" command. 

Hope it helps. 

Molody