mac forwarding database

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Oct 17th, 2007
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Hi all, can anyone tell me about the mac database on my switches, I know it maps a mac to a port, but what about the uplinks to other switches, does it cache all mac addresses that go to the other switches? and is it all cleared when the switches are rebooted ?

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Kevin Dorrell Wed, 10/17/2007 - 04:14
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Yes, any MAC addreses it sees on the uplinks are also added to the database. If your network is more than just a couple of switches, and if you do a show mac-address, you will probably see most of the MAC addresses are on the uplinks.

When a switch sees an interface go down, it will clear all the MAC entries that are on that port. If a switch reboots that is not directly connected to the one you are looking at, the MAC entries are not cleared immediately. Instead, the Spanning-Tree sends out a "Topology Change Notification", and this causes the switch to set a 15 second aging time on the MAC table entries.

Does that answer your question OK?

Kevin Dorrell



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