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Need Cisco command to convert mac address to ip address

BPGInfotech
BPGInfotech asked
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Last Modified: 2009-12-16
I have a Cisco 3560 that we are trying to determine the ip address of a device that is connected to a given port... We have run "show mac-address-table" and have the mac address but now need to know how to convert that mac address into an IP Address.  Does anyone know the command?
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I thought doing a "show arp" will only give you the mac address and the port right?  Since the device is Layer 2, it doesn't really understand IP addresses.

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Ok... I am going to split the point between the two but give the majority to donjohnston and her is the reason why... I had already stated that I was able to do a show mac-address-table on the switch that I wanted to find the IP address.  By doing this command I can see the mac address associated to a given port.  donjohnsoton mentioned the default gateway and that is the key point here... I tried to do a show arp on our router and it only showed info on what is connected to that device... really just external IP Addresses... but our Firewall I did the show arp and I was able to get the ip address of all devices with their mac address... I then cross referenced the command I did on the switch to get the matcing IP address.  We have a ASA5510 firewall and the show arp command gave me the info...

Thanks for your resposes
Don JohnstonInstructor
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Commented:
>I thought doing a "show arp" will only give you the mac address and the port right?  Since the device is Layer 2, it doesn't really understand IP addresses.

The 3560 is a multilayer switch. As such, if IP routing is enabled (and if the device is communicating with the switch), then it's IP address, MAC and port will be displayed in the ARP cache of the switch.

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Commented:
Show arp on teh 3560 switch gave IP and MAC but only from two of my servers and my firewall the ASA5510.  But the "show mac-address-table" on the 3560 gave me the mac and port... which was half of my issue I knew what port was in question.  So by doing the "show arp" on my ASA I got a list of IP Addresses and Mac Addresses... I then matched the Mac from the mac-address-table command to get the IP Address.
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