'show arp' shows VLAN interface and not physical?

Answered Question
Jan 14th, 2008
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Hi everyone,


I was wondering how I can find out the actual physical interface a MAC is learned on instead of the VLAN interface.


For example, on my switch I have:


show arp


Internet 192.168.0.25 - 0018.bad3.cb41 ARPA Vlan2

Internet 172.16.1.25 0 0009.0f06.ff0c ARPA Vlan3



The VLAN interface doesn't tell me which physical port it came out of...


Is there a way to find that out?


Thanks in advance.


Ali

Correct Answer by Jon Marshall about 9 years 5 months ago

Ali


You need to look at the mac-address table eg.


DC-BBP-F00-DS2#sh arp | include 000e.7fb4.f819

Internet 10.231.199.43 3 000e.7fb4.f819 ARPA Vlan40

DC-BBP-F00-DS2#


DC-BBP-F00-DS2#sh mac-address-table address 000e.7fb4.f819

Legend: * - primary entry

age - seconds since last seen

n/a - not available


vlan mac address type learn age ports

------+----------------+--------+-----+----------+--------------------------

Supervisor:

* 40 000e.7fb4.f819 dynamic Yes 10 Po1


As you can see the actual interface this mac-address was learned on is po1 which happens to be an etherchannel connection to another switch.


HTH


Jon





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Correct Answer
Jon Marshall Mon, 01/14/2008 - 13:07
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Ali


You need to look at the mac-address table eg.


DC-BBP-F00-DS2#sh arp | include 000e.7fb4.f819

Internet 10.231.199.43 3 000e.7fb4.f819 ARPA Vlan40

DC-BBP-F00-DS2#


DC-BBP-F00-DS2#sh mac-address-table address 000e.7fb4.f819

Legend: * - primary entry

age - seconds since last seen

n/a - not available


vlan mac address type learn age ports

------+----------------+--------+-----+----------+--------------------------

Supervisor:

* 40 000e.7fb4.f819 dynamic Yes 10 Po1


As you can see the actual interface this mac-address was learned on is po1 which happens to be an etherchannel connection to another switch.


HTH


Jon





paolo bevilacqua Mon, 01/14/2008 - 13:23
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Let me put it in another way to add to Jon's great example:


Show arp will tell you which layer 3 interface has the address.

But the info you want is at layer 2, so you need a layer 2 command, show mac-address-table exactly.


amiralisetoudeh Mon, 01/14/2008 - 15:53
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Thanks to both replied - very helpful in understanding the difference between the two commands.

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