Why virtual MAC address for Etherchannel not mirroring interface MAC ?

[GabrielART]

Hello, 

I am trying to check the MAC address for the PO1 and validate that is using the MAC address of the first interface of the port-channel by using Georg Pauwen commands shown above. However, the MAC address of the PO1Switching, Catalyst 2000, LAN Switching is not matching either interfaces configured on these two interfaces F0/23 or F0/24 as shown below. Any explanations why?

Group Port-channel Protocol Ports

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

1 Po1(SU) LACP Fa0/23(P) Fa0/24(P)

2 Po2(SU) LACP Fa0/21(P) Fa0/22(P)

*******************************************************************************************

Acc3#show inter po1

Port-channel1 is up, line protocol is up (connected)

Hardware is EtherChannel, address is 00e0.8f97.0342 (bia 00e0.8f97.0342)

****************************************************************************************

Acc3#show inter f0/23

FastEthernet0/23 is up, line protocol is up (connected)

Hardware is Lance, address is 00d0.d38a.2217 (bia 00d0.d38a.2217)

*****************************************************************************************

Acc3#show inter f0/24

FastEthernet0/24 is up, line protocol is up (connected)

Hardware is Lance, address is 00d0.d38a.2218 (bia 00d0.d38a.2218)

[Flavio Miranda]

@GabrielART 

 Is it a layer2 Po or a Layer3 Po? 

[GabrielART]

Hello again Flavio, and thank you again for the feedback. In this example it is a layer 2 switch, however, because you mentioned that I also tested test on layer 3 switch and the results were the same. I am not sure where PO1 MAC address is coming from. Any help would be great, thanks. 

[Flavio Miranda]

I asked because with layer3 port-channel you can configured static ARP which could explain. But It seems this not the case. 

 And indeed the Mac address should be the Mac address of the first interface.

If you run show Mac address table , this Mac address is associated only with the Port Channel?

[GabrielART]

I checked the MAC address table and indeed, it is using the physical MAC address of the interface associated with PO1. However, the PO1 virtual MAC (00e0.8f97.0342 (bia 00e0.8f97.0342) still not sure where it is coming from. Might be a PT glitch. 

[M02@rt37 · Accepted solution]

Hello @GabrielART 

Please find here clarification:

https://community.cisco.com/t5/data-center-switches/arp-resolution-with-port-channels/td-p/3774741

[GabrielART]

Hello again M02@rt37, 

Interesting explanation. We need to correct Google and other few sources claiming that the MAC address of the Etherchannel comes from the first physical interface. What Peter Paluch said makes sense, but it is also intriguing how that is not consistent; some times the Etherchannel will come up with it is own MAC, and sometimes - I've seen it myself - will use the MAC address of the first configured physical interface. I thought that maybe it was using some odd calculation like IPv6 EUI-64. Good stuff. Thanks again.