MTU on Nexus switches - CDP and vCenter

Some time ago I’ve installed the new core switches for a customer: a couple of Nexus 7000, a couple of 5000 and twelve Nexus 2232TM, Virtual port channels, VLANs, Radius auth and so on.. all the usual configs a good network engineer does.

2013-06-20_16-26-15_HDR

Since the Nexus 5000 are connected to an iSCSI storage I’ve configured Jumbo frames.

Customer called complaining that MTU isn’t correctly set and I must fix it. The attached a screenshot from vCenter showing “MTU: 1500”.

screenshot_mtublog

This is well documented in Cisco Nexus 5000 QOS configuration guide:

The show interface command always displays 1500 as the MTU. Because the Cisco Nexus device supports different MTUs for different QoS groups, it is not possible to represent the MTU as one value on a per interface level.

CDP will always show MTU value 1500, the correct command to check the MTU of the interface is:

<kbd>show queuing interface ethernetx/y</kbd>
 
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