missing mac address-table info?

[Andrew Cormier]

Hi, probably a newb question but...

I do show int statu for gi1/0/15

Gi1/0/15                     connected    1          a-full  a-100 10/100/1000BaseTX

If I do show I get nothing.

sho mac address-table interface gi1/0/15
          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----

Make sense? Am I missing somethign here?

[Andrew Cormier]

Hmm.. nothing? I have actually about 7 ports on the switch that are up and connected but nothing in the mac address-table.

[jawad-mukhtar]

Whats IOS version, try upgrading IOS.

[Andrew Cormier]

Cisco IOS Software, C3750 Software (C3750-ADVIPSERVICESK9-M), Version 12.2(46)SE, RELEASE SOFTWARE (fc2)

I know the ip of some of the devices on some of the ports and if I ping them from the switch the mac table gets updated.. 15 min later (or so) it clear those entries out again.

[jawad-mukhtar]

do you have hardcorded that ports as Access Ports or trunk.

[jawad-mukhtar]

Hey Andress

ON Specific Access interface run this command

spanning-tree portfast

and then observe

[Andrew Cormier]

Didnt seem to do much

CISCO3750-1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
CISCO3750-1(config)#int gi1/0/3

CISCO3750-1(config-if)#spanning-tree portfast
%Warning: portfast should only be enabled on ports connected to a single
host. Connecting hubs, concentrators, switches, bridges, etc... to this
interface  when portfast is enabled, can cause temporary bridging loops.
Use with CAUTION

%Portfast has been configured on GigabitEthernet1/0/3 but will only
have effect when the interface is in a non-trunking mode.
CISCO3750-1(config-if)#end
CISCO3750-1#show mac address-table int gi1/0/3
          Mac Address Table
-------------------------------------------

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
CISCO3750-1#

[dbergman13]

Were you able to find a solution for this issue? I am experiencing the same thing.

[pwwiddicombe]

What is at the other end of that link?  Is it a redundant link to a server (in which case there may not be packets inbound on that interface), hence the table is empty ?

[dbergman13]

Actually, it is non-windows devices such as Alarm panels, marquees, etc. None of them have redundant links and some canon printers are experiencing the same thing where the mac address will disappear from the mac address-table after about 10-15 mins. These are connected to the 2960 and 3650 switches.

[pwwiddicombe]

OK - the switches have a default address-learned aging time, which can be adjusted if you really want that - normally the only downside is where you have many devices being connected and disconnected.    Default is 5 minutes.

Use the mac address-table aging-time global configuration command to set the length of time that a dynamic entry remains in the MAC address table after the entry is used or updated. Use the no form of this command to return to the default setting. The aging time applies to all VLANs or a specified VLAN.

[dbergman13]

I tried changing the mac address table global aging time to 1800 sec (30 mins) and the mac address still disappeared. I noticed that most of the mac address entries in the mac address table show the port as the trunk port and not the access port that it is plugged into. Is that normal? I even tried assigning a static mac entry for the port and after about 24 hours it will drop connectivity and only respond if I ping from the device or shutdown and re-enable the port.

[pwwiddicombe]

Seeing MAC addresses on an uplink port can mean one of several things...

1.  You have an alternate path to the device

2.  Somehow you have the MAC address duplicated in another end device

       (from cloning industrial devices, maybe ?)

3.  You have IP Device-tracking enabled on the switch.  It can do odd things, from messing up DHCP duplicate address detection and causing odd MAC table entries.  If you don't NEED it, try disabling it.

[dbergman13]

1. I noticed a loop and resolved that but it is still happening and at multiple sites.

2. I do not see duplicate devices or mac address entries and we do not clone.

3. We have device tracking disabled and it still occurs.

I have one site I am testing right now to see if the mac address-table aging time of 3600 works and keeps the mac addresses there. (I just found out that the best practice from cisco is an aging time of 3600) I will let you know the results.

[dbergman13]

Update: The mac address aging time increase did not work and the device's mac address would still disappear from the mac address table. 

We are now experiencing the same thing with Ubuntu servers in our ESX virtual environment. ESX and Windows VMs are fine though and are pingable.