08-26-2010 01:13 AM - edited 03-06-2019 12:39 PM
Suppose you have a switch and that the mac-address-table has the following entry:
mac address port vlan
1111.1111.1111 fa0/1 10
If the dispositive with mac address 1111.1111.1111 is connected to port fa0/2 in the same vlan, I
wondered if these entries are possible in the same time:
mac address port vlan
1111.1111.1111 fa0/1 10
1111.1111.1111 fa0/2 10
In other words, I wondered if the switch checks the presence of the same mac address on two
different ports in the same vlan and, in this case, delete the first entry as soon as it learns the
second one, or if it is possible to have multiple entries until the older one normally timed out.
If I have understood, it is possible to have multiple entries if they belong to different vlans, because
the switch considers separately the mac address table for different vlans: I have seen a question
where the answer said that it was possible.
Solved! Go to Solution.
08-26-2010 05:56 AM
Hello,
It is possible to have a MAC address registered under two ports. But on
Cisco Switches, it is supported when you configure it manually. When you are
dynamically learning, as soon as a port goes down, switch will remove the
MAC associated with that port. If the MAC is still registered on one port
and you see the same MAC on another port, switch will remove the old entry
and put the new entry in there. If this happens too often with the same MAC,
then switch will generate an error log (MAC flap error).
Hope this helps.
Regards,
NT
08-26-2010 05:56 AM
Hello,
It is possible to have a MAC address registered under two ports. But on
Cisco Switches, it is supported when you configure it manually. When you are
dynamically learning, as soon as a port goes down, switch will remove the
MAC associated with that port. If the MAC is still registered on one port
and you see the same MAC on another port, switch will remove the old entry
and put the new entry in there. If this happens too often with the same MAC,
then switch will generate an error log (MAC flap error).
Hope this helps.
Regards,
NT
08-26-2010 06:15 AM
Thanks for your good answer and for having remembered me the differences with manually entries.
Now I remember that, reading the 2960 configuration guide some time ago, I had understood that
there was more work then I imagined on handling the mac-address-table by the switch.
A simple question about the forum: how can I give a vote to your answer?
08-26-2010 07:14 AM
Hello,
Glad that I was able to help. Just click on the stars below the answer to
rate the answer.
Regards,
NT
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