System Class CoS versus Host-Control Full

[Bradley Urberg Carlson]

Let's say that UCS System QoS has Enabled Priorities:

- Platinum, CS5, 30%, no-drop

- Bronze, CS2, 20%

- Best Effort, Any, N/A%

If a UCS QoS Policy called "MostlyBronze" is configured with "Priority: Bronze" and "Host Control: None", then all traffic received on a VMnic associated with policy MostlyBronze (CS0, CS2... whatever) will be stamped with CS2, and queued using Bronze weight 20% as defined in the QoS System Class.

But what happens if "Host Control: Full" is checked in policy MostlyBronze?  Are packets received on a MostlyBronze VMnic which are unmarked (CS0),  still stamped with CS2 and given 20% queue weight?  Or, is the CS0 "trusted," and the packets are treated as Best Effort?

Similarly, if "Host Control: Full" is checked, and the received packet is marked CS5, is it queued as Bronze (20% weight, drop-enable), but forwarded with unchanged CS5?  Or is the received CS5 marking "trusted" and it is queued as Platinum (no-drop), even though the vmnic is associated with policy MostlyBronze?

[Justin Welch]

Hello,

There are two different QoS modes available for each virtual adapter — 1) Host control NONE, or 2) Host control FULL.  The NONE mode is stating that COS markings from the server will be ignored and overwritten with the virtual adpater’s COS setting in UCS Manager.  The FULL mode is stating that COS markings from the server will be preserved and used to determine which COS queue each packet is serviced from on the Cisco VIC.

Hope this helps,

Justin

[Bradley Urberg Carlson]

Thanks, Justin.  Does that mean that the Priority drop-down does absolutely nothing, if HostControl:Full is clicked?  Whether the Priority is set to Platinum or Bronze would not matter, because CoS is trusted?

Or, perhaps does the Priority drop-down still have a function, even when HostControl is Full, such as marking and classifying received packets which are untagged/CS0?

[Justin Welch · Accepted solution]

Hello,

If host control is set to FULL we do not mark frames with QoS settings configured from UCSM, we base CoS tagging off of the OS. Just so you are aware CS0 = best effort in UCS.

Does this answer your question?

Thanks,

Justin

[Bradley Urberg Carlson]

Thanks.  It sounds like the operation is basically equivalent to old catalyst "trust cos" or "set cos X".

Web design: If the "Priority:" drop-down does nothing, whenever HostControl:Full is clicked, then the dialog is misleading.  Either "HostControl:Full" should simply be another option on the Priority: drop-down (so you can choose to EITHER set priority, OR set hostcontrol); or else selecting Hostcontrol:Full should grey-out/remove the Priority drop-down from the dialog, to show that setting Priority is a no-op, once HostControl:Full is set.