6509 switchport question about mac-address from attached device

Unanswered Question
Mar 25th, 2008

My question stems from 6509 blades that have some problem ports.

The ports will show up/up but will not pass traffic. I have found up to 6 ports per blade that are doing this. The attached device shows a connection, but canot get an IP address and the device mac-address does not populate the port table.

Reseating the blade seems to correct the problem, allowing me to use the ports.

But my question is, at what point does the mac-address of the attached workstation or device show up on the switch port that links that device to the network (found by using "sh mac-address int fx/x)?

What causes a successful entry of the device mac-address to the port?

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Overall Rating: 5 (2 ratings)
Jon Marshall Tue, 03/25/2008 - 13:58


As soon as something tries to communicate with the device connected to the port or as soon as the device on the port tries to communicate with something else the mac-address of the device should get added to the mac-address table.

On a normal PC running windows this is usually pretty instantaneous.


wilson_1234_2 Wed, 03/26/2008 - 05:26

Thanks for the reply John,

But I was hoping for the exact thing that populates the switch mac-table to the particular port?

It can't be as soon as the device is connected, because the port shows up/up but no mac-address.

I have seen printers also that the table will time out and see nothing on the port, but as soon as you ping, the port has the mac-address.

I was wondering what exact sequence happens that causes the port to have the mac-address.

Is there a sequence on the MAC/LLC layer that makes it happen?

Jon Marshall Wed, 03/26/2008 - 05:30


The mac-address table will be populated with the device mac-address (assuming there is space left) as soon as either

1) the device on the port arps out or sends a packet to another device

2) A different device arps out for the device connected to the port.

If the device is inactive for a certain amount of time ie. it doesn't talk to any other device and no other device talks to it it's entry will be timed out.

I may not be explaining this very well.


wilson_1234_2 Wed, 03/26/2008 - 07:16


That is what I was looking for, I didn't knowq if it was the arp that caused the mac to populate the switch port or not.

So on the ports that are not working, no arp is taking place on the port, so no communication happens, even though the port is receiving keepalives from the

NIC to show the up/up condition?

Jon Marshall Wed, 03/26/2008 - 07:18


Yes, keepalives are working at the physical layer in this sense. Mac-addresses only come into play when the device is communicating with another device.




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