PC mac-address being retained by the IP phone

[Karl Rogers Muller]

Guys,

I'm facing something interesting here.

The situation is the following: I have Cisco IP phones in the whole building and some people that moves from desk to meeting rooms and back to desk (lots of meeting). If a person connects her laptop to an IP phone (in the meeting room), and after the meeting this person then comes back to her desk (and connects her laptop in the PC-port from an IP phone), then we got an issue: the laptop simply doesn't work.

Taking a look at the mac-address table from the switch, we could conclude that the IP phone from the meeting room keeps informing the laptop mac-address through the switch port, therefore when the person connects the laptop in her desk, the switch learns the mac from two different ports, causing a flapping.

We realized that turning off the IP phone from the meeting room solves the problem - but, it's not indeed a good option.

Do you guys have any idea how could I decrease IP phone mac-address table's aging time?

Thanks!
Karl

[paolo bevilacqua]

The phone is not informing the switch about anything. The switch has his own mac-addreass aging and the only thing that the phone play a role in, is when the phone is disconnected, or tunred off, all entries related to that switch port are cleared.

That beaing said, as soon the PC is connected to a different port, the mac-address-table should be update, if it is a cisco switch you should see a message of the for MAC flap.

If it is not a Cisco switch, check with the vendor.

[Karl Rogers Muller]

Paolo,

Thanks for repplying!

I definitely agree with you regarding the mac-address table, and it should be update and etc.

The point is: I personaly put a switch in my desk and an IP phone. When I move the PC from one port to another, the mac address table is updated in the mac address from this PC is learned in the new port.

Now, assume that there is an IP phone (Cisco 6921) connected in the same switch. The PC is connected at the PC-port of the IP phone. Then, I mode the PC, from this PC-port (at the IP phone) and connect it and any other port from the switch. The mac appears at both ports: the IP phone port and the new port at which the PC had been connected - an then I got the problem.

I understand that the switch is working fine, as I'm moving the PC from one port to another and I face no problems. But, if I move the PC, from the IP-phone PC port to another port within the switch, then it doesn't work.

I asked about aging time just because it seems that the IP phone is not flushing this address from its table, and somehow it is still advertising it to the switch.

Thanks,

Karl

[paolo bevilacqua · Accepted solution]

I understand that the switch is working fine, as I'm moving the PC from one port to another and I face no problems. But, if I move the PC, from the IP-phone PC port to another port within the switch, then it doesn't work. 
I asked about aging time just because it seems that the IP phone is not flushing this address from its table, and somehow it is still advertising it to the switch. 

No, the HP switch is not working fine, and the problem is not with the phone, but with the HP switch.

As explained above already:

The phone by itself does not 'advertise' anything, ever.

When you move a PC from a port to another of your HP switch, all MAC entries from the port that goes down are immediately removed, then the switch learns the mac address on a new port.

But when there is a phone in between switch and PC, and you move the PC from a phone to another, no switch port changes state ever, then evidently HP switch fails to re-learn the PC MAC address to a new port, as frames start coming in again from there.

That is not a problem with Cisco switches that handle both scenarios above correctly, so you will have to fix on the HP switch.

[yahsiel2004]

Karl,

Are you using port-security with mac-address sticky? If so, you have to delete the learned "static" mac addres from the port. Can you post an example config of your swtich?

HTH

Regards,

Yosh

[Karl Rogers Muller]

Yosh,

The port security is configured, but we are not using the sticky option.

Actually, the ip telephony is Cisco, but the switch is HP A series.

May I post here the config from this HP switch?

Thanks,

Karl

[yahsiel2004]

Yes

HTH

Regards,

Yosh

[Karl Rogers Muller]

Hey Guys,

I did a couple more tests, just to be sure, and it really seems to be something related to the HP switch.

I appreciate your help, Paolo and Yosh, and I'd like to say that this forum helps not only giving a direct answer to a specific issue, but also by arguing and moving towards the issue resolution.

Best Regards,
Karl Müller

[paolo bevilacqua]

Thank you for the nice rating, and good luck!