Cannot locate MAC address from VMWare ESXi server on Cisco 3850 switch

[Scubadiver6]

I'm trying to label switch ports on servers 20 miles away from me - I do not have immediate access to them.  I have a Dell server connected to a Cisco 3850 switch.  The servers are running VMWare 6.7.

Switch is running 16.12.5b

I know the MAC address of the cards.  I get them from the the stickers on the cards, from Dell iDRAC 9, and from VMWare vCenter and ESXi command line.  I just cannot find them on the switch via:  show mac address-table

This is happening across all my servers - even in my test lab - using both Dell and Cisco switches.

On one of my test servers in my lab:

• I pulled the NIC and wrote down the MAC address that is physically printed on the card.
• I logged into the iDRAC of the server, and verified the MAC address visible via the iDRAC is exactly the same as on the card.
• I log into VMWare and I can see the same MAC address via vCenter and via ESXi command line.  (The card is only assigned to a vSwitch)
• I log into my switch, look at the switch port, and can see a MAC address "close" to the one I'm looking for - but not 100% match.

In my lab, the only thing connected to the 3850 is the NIC above - nothing else.  Its not connected to my Corporate network at all.

To make things more confusing, I repeated the same procedure above on a brand-new Dell server - without an OS - and I have the same issue.  When I install Windows on the server, I can then see the MAC address on the switch.  NOTE:  After I install Windows, I do not assign an IP to the NIC, and DHCP is not running.

Anybody know/explain what is happening, and how I can map my ports?

[Georg Pauwen]

Hello,

odd indeed. What happens if you shut/no shut the interface ? I assume it is just a standard port configuration, without port security ?

[Scubadiver6]

Correct - no port security....  The 3850 in my lab has a very minimal configuration on it....  

Corp-WS-C3850-48XS1#show port int tengigabitethernet 1/0/27
Port Security : Disabled
Port Status : Secure-down
Violation Mode : Shutdown
Aging Time : 0 mins
Aging Type : Absolute
SecureStatic Address Aging : Disabled
Maximum MAC Addresses : 1
Total MAC Addresses : 0
Configured MAC Addresses : 0
Sticky MAC Addresses : 0
Last Source Address:Vlan : 0000.0000.0000:0
Security Violation Count : 0

[Jon Marshall]

I just checked our vsphere 6.7 on 3750 switches and not seeing same issue. 

Have you tried creating a VM and tracing that based on it's IP ? 

Jon

[paul driver]

Hello

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@Scubadiver6 wrote:

I log into my switch, look at the switch port, and can see a MAC address "close" to the one I'm looking for - but not 100% match

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That mac-address is possibly related to the system mac of the server and not of the nic - You can verfiy this by checking the system bios of the host server.

[Elliot Dierksen]

As @paul driver mentions, the server is likely not sending frames with its own mac address. The would certainly be the case if the physical adapter is in a vswitch that is used just for guest traffic. You can look at the ESXi host config and see CDP neighbor information (assuming your switches have CDP enabled).

[tomeq82]

we have observed same thing on Nexus 7k/FEX 2k switches and ESX boxes - we can't see any mac on the switch port (sh mac address table interface xxx) while LLDP/CDP shows mac of the NIC on the server close, but not the same as physical connected mac After quick investigation it comes out it is logical interface mac with +1 byte to physical nic.... LLDP shows logical, while gui shows physical mac. It is quite counterintuitive and I think it worked well some time ago, and changed with some ESX patches/version changes.

[networkname98]

Hi Tomeq82

I have come across the same.  The MAC address seen at the switch is one byte different from the MAC address we see on the ESXi host.  Man! that is very frustrating. Especially when we cannot enable CDP due to security protocol.  Its now impossible to work out which server port is connected to which switch port without tracing cables! 

(I've noticed that this does not happen on DELL switches - you see the same MAC address at both the switch and server ends)