N5k Jumbo Frames not correctly displayed

[mateja.jovanovic]

Hello,

We have two 5548UP with 6.0.2-N2 with N2k in FEX, single homed, and FCoE, and we´ve been facing performance issues.

I´ve configured the network-qos policy to permit 2158 MTU for the FCoE, and 1500 MTU for default traffic. On the statistics of all interfaces (even the ones where only Ethernet is going) I can see a bunch of Jumbo Frames.

Here´s the Network QoS config:

policy-map type network-qos fcoe-default-nq-policy
    class type network-qos class-fcoe
      pause no-drop 
      mtu 2158
    class type network-qos class-default
      mtu 1500
      multicast-optimize

 system qos
   service-policy type network-qos fcoe-default-nq-policy

All the "show interface" and "show queuing interface" commands display the MTU of 1500, while, for example, on the interface towards the CORE´s (6500) where there is no FCoE, only ethernet, there are bunch of Jumbo Frames.

Any idea where these Jumbos are coming from?!? 

[richbarb]

Hi Mateja,

In the Nexus 5500 platform, any frame size higher than 1518 is considered jumbo frame.
It seems doesn't makes sense if you don't have configured jumbo frame in your network/devices and you see these counters incrementing.

But if you includes ethernet and the dot1q tag(if trunking) which is 18 plus 4 for a total of 22 bytes of header. So if the host is sending/receiving frames with more than 1496 bytes of data you would see the Nexus 5k count these frame as jumbo.

Regards,

Richard