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MLOM Slot vs Chassis Slot in ESXi?


Hi all, we're in the process of replacing much older UCS hardware (6120's serving B440M2's with M81KR adapters) with 6248's serving B200M4's with VIC 1340 adapters in chassis using 2208XP i/o modules.  I'm presenting 10 vNIC's to the servers.


While installing ESXi on the first of the new blades, I noticed that the first five NICs show as:


MLOM Slot: relative bdf 03:00.0


With the number going from 3 through 7.  The next five NICs show as:


Chassis slot f; function 0; relative bdf 03:00.0


With the same progression of that bdf number 3 through 7.



I can't find any documentation on why these show up with the different presentation between the first five and remaining five, or if there's any consequence to it from either an efficiency of throughput perspective.  From ESXi's perspective they all show the available speed as being a match to the port channel that is serving them on the back end.  All our QoS policies are set to either platinum or best effort with line rate limit in case that's relevant, but prior to doing that, the vNIC's that had Bronze defined were showing in vmware as 1gbps cards so I changed them to best effort to get line rate.


Thanks in advance

4 Replies 4

Walter Dey


The internal PCI architecture of your old and new blades are not identical; therefore Cisco doesn't support the migration of the service profile.

This has been discussed alot, see eg.

ESXi/ESX host loses network connectivity after adding new NICs or an upgrade (2019871)

How VMware ESXi determines the order in which names are assigned to devices (2091560)


Sorry, I think I was confusing with the back story; these two systems are parallel and the service profiles, etc. are all being set up independently; no copying of configs, etc.  I'm just trying to figure out the difference, and consequences, of what was ten similarly named NICs presented to ESXi by older UCS and now seems to be five MLOM NICs and five "Chassis" NICs.

Agreed,  I don't think the question was answered..

Cisco Employee
Cisco Employee

The 13xx VIC utilize two PCI Lanes which we refer to as Admin Host Ports in the Service Profile.  As such, VMware thinks these are two different sources and identifies the vNIC/vmnics different based on which host port they utilize.  Host Port 1 should should up as MLOM and Host Port 2 will show up as Chassis Slot.  As by default we round robin between the admin ports, having half say MLOM and half say Chassis Slot would be expected.


Were you to have a 1380 also installed, you will see the same behavior, but instead of MLOM, it will report MEZZ.



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