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Static mac "12:34:56:78:9a:bc" in AKS

Raphael Campos Silva 1 Reputation point
2021-05-17T22:02:18.01+00:00

Hello,

I create a small AKS cluster and I saw that 2 nodes communicates through the same mac address "12:34:56:78:9a:bc", and this is why (https://social.msdn.microsoft.com/Forums/Lync/en-US/be3e4ab1-7b0e-42d0-82a6-08b640dd51c3/strange-quot123456789abcquot-ethernet-addresses?forum=WAVirtualMachinesVirtualNetwork). Even in the same subnet, the destination mac addr. is "12:34:56:78:9a:bc".

So my questions are: 1) I couldn't find it - Is there a place in official AKS documentation talking about this static mac "12:34:56:78:9a:bc" used in VNet?; 2) it is true to say that this happens in all AKS instances?

I ping from node 1 to node 2, and test in both instances (Standard_DS2_v2 and Standard B2s), and the behavior is the same.

From node 1 (10.240.0.4 - 00:0d:3a:59:76:13)
azureuser@aks-nodepool1-23965286-vmss000000:~$ arp -a | grep 10.240.0.35
aks-nodepool1-23965286-vmss000001.internal.cloudapp.net (10.240.0.35) at 12:34:56:78:9a:bc [ether] PERM on eth0

From node 2 (10.240.0.35 - 00:0d:3a:30:5c:2c)
azureuser@aks-nodepool1-23965286-vmss000001:~$ arp -a | grep 10.240.0.4
aks-nodepool1-23965286-vmss000000.internal.cloudapp.net (10.240.0.4) at 12:34:56:78:9a:bc [ether] PERM on eth0

I appreciate if somebody could help me, tks

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  1. shiva patpi 13,366 Reputation points Microsoft Employee Moderator
    2021-05-19T01:48:28.603+00:00

    Hello @Raphael Campos Silva ,
    Thanks for your query !

    You can see the detailed answer of your query at https://www.untangled.eu/2017/07/networking-in-microsoft-azure-part-1/
    I just tested for Linux Azure Virtual Machines in same VNET and different VNET - it's the same MAC Address.
    Reason is explained in the above article.

    It's not only for AKS node instances any Virtual Machines in Azure will use the same MAC Address i.e. Every ARP request you send out on a Azure Virtual Network asking the MAC address for a specific IP address is always answered with the same simple MAC address: 12:34:56:78:9a:bc.

    That is because you are on a shared platform and the Virtual Network or VNET is a Layer 3 overlay instead of Layer 2 on the OSI model where you have the datalink layer. You can’t change a VM or other devices on the Azure platform and put this on a different switch port. That power was removed from you as a user and Microsoft created an abstraction layer on top of their infrastructure.

    Hope that helps in understanding !

    4 people found this answer helpful.
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