'show arp' shows VLAN interface and not physical?

Answered Question
Jan 14th, 2008

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

I have this problem too.
0 votes
Correct Answer by Jon Marshall about 8 years 10 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

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

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

Thanks to both replied - very helpful in understanding the difference between the two commands.

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