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New Member

discovering MAC addresses for Switch ports

Hello and thanks for looking at my question,

My company has inherited a network which has some very poor documentation. We really have no clue, nor does the customer, what machines are connected to what switch ports.

My co-worker and I were discussing the best way to find this out with the least amount of effort, but can't agree on a single solution. Any recommendations would be greatly appreciated.

Thanks.

Sincerely,

Brent

5 REPLIES
New Member

Re: discovering MAC addresses for Switch ports

on the switch issue a

show arp.

this will give you the layer 2 & 3 address.

you can then perform a nslookup on the ip to find out the host information.

New Member

Re: discovering MAC addresses for Switch ports

Hi bmutcherson,

Thanks for your reply.

That was my co-workers suggestion as well. We were wondering if there may be some tool somewhere that we don't know of that will simplify this process.

As you can imagine, doing an nslookup on hundreds, (around 500 addresses I believe), will take days.

Thanks.

-Brent

New Member

Re: discovering MAC addresses for Switch ports

Brent,

After you do the 'sho arp' and now have MAC to IP translation, do a 'sho mac-address table' to show MAC to port translation. Save both tables to an Excel spreadsheet and tie them together. You should be able to come up with a good cross reference table (depending upon your Excel skills).

This also gives you a switch-by-switch breakout. It's also a very helpful troubleshooting method to find rouge devices and shut down a port (for instance).

Hope this is helpful.

Jim

New Member

Re: discovering MAC addresses for Switch ports

Hi Jim,

Thanks for the advice. I wasn't aware you could save the tables to a Spreadsheet. (doh!!) This just might do it.

Thanks again!

-Brent

New Member

Re: discovering MAC addresses for Switch ports

Brent,

Depending on the terminal program you're using, you can always cut and paste or save the session to a text file. Then edit the unnecessary stuff out and import to Excel.

Glad I could help.

Jim

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