How To Refresh MAC Table?

- J
- JohnD
  
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posted
16 years ago

Thu, Feb 21, 2008 9:37 PM

I've got a stack of 3750s running 12.1.14.

I've got CAT5 ethernet cables plugged into ports Gi3/0/12 and Gi3/0/18. The LEDs are green. Show counters indicates that traffic is going through these ports. But for some reason I can't get the MAC address of the devices plugged into this port (which means I'm going to have to trace a LONG cable run through a very tight wiring cabinet).

CoreSwitch#sh mac-add int gi3/0/18 Mac Address Table

-------------------------------------------

Vlan Mac Address Type Ports

---- ----------- -------- ----- CoreSwitch#

I've run IP scans on all our subnets, I've done clear arp -- nothing seems to work. I'm fairly certain there's an ethernet NIC on the other end and that it's got a MAC address -- it has to, right?

Is there any way to force a refresh of the MAC table? Is there any way to trigger a broadcast? (Would pinging 255.255.255.255 work?)

Thanks

- M
- Merv
  
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posted
16 years ago

Fri, Feb 22, 2008 12:51 AM

if you have a spare port on the switch then you could set up a span/ monitor port to span the traffic on each port ( one at a time) to th emonitor port where you could connect a PC runing Ethereal sniiffer software *free) to see if you can see anything useful to identify the devices in question

- H
- headsetadapter.com
  
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posted
16 years ago

Fri, Feb 22, 2008 1:24 AM

Sometimes when interface configured with a static IP address, which is not correct, the host does not communicate to the port, and switch has no MAC address. I've seen it just two days ago - had an Linux appliance with a static IP address configured on the interface. Plugged interface to the switch, port says "Connected", but no MAC address in the CAM table. After I changed an IP address to whatever it should be for the VLAN - NIC started to communicate, and MAC address appears on the port.

Good luck,

Mike CCNP, CCDP, CCSP, Cisco Voice, MCSE W2K, MCSE+I, Security+, etc. CCIE R&S (in progress), CCIE Voice (in progress)

------ Headset Adapters for Cisco IP Phones

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