mac, arp table

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Richard Burts Fri, 02/16/2007 - 11:53

Aksher

I am not sure that I fully understand your question. But based on what I think you are asking here are answers:

- the mac table is built and maintained locally and independently on each switch. It is not distributed in a layer 2 environment.

- the arp table is populated locally on a switch for any address for which it has issued an arp request and received an arp response, whether it is a directly connected interface or a remote interfacee. The arp table is not replicated accross other switches in the layer 2 environment.

If I have not understood something correctly then perhaps you can clarify.

HTH

Rick

Richard Burts Fri, 02/16/2007 - 13:02

Aksher

This is a very different question from what I thought that you were asking at first, so thank you for clarifying.

In a switch there is an arp table and a mac table and they are very different and serve different purposes. The arp table is built when the switch (the management interface of the switch) sends an arp request and receives an arp response. This would happen when the switch management interface needs to communicate with other devices in the network. The arp table will usually be fairly small in the switch. The arp table does not have anything to do with how the switch forwards packets/frames. The mac table is built by the switch to help it forward frames through the network. When a frame arrives on one interface of the switch, the switch looks at the destination mac address and does a lookup in the mac table to find which interface will be the outbound interface. So the mac table is essential to how the switch forwards frames in the network.

Another way to look at it is that the arp table is a table of layer 3 information and supports layer 3 communication. The mac table is purely a table of layer 2 information and supports layer 2 communication.

HTH

Rick

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