Nexus 5500 FCoE and Jumbo MTU

I happened across an interesting scenario this morning while I was doing configuring jumbo MTU of 9216 on the Nexus 5500 switches in our lab.

I wanted to enable jumbo frames and with Nexus 5500s you have to do this with a QoS policy map. Here are the steps:

  1. Create a new policy map of type network-qos
  2. Add the default network-qos class type of class-default
  3. Configure the MTU to 9216
  4. Add the new policy map to system qos

More about this in the Cisco Nexus 5500 QoS Configuration Guide – QoS Configuration Guide

As soon as I added the new network-qos policy map to the system-qos I checked the configuration using the command “show queuing interface e1/20”

As you can see from the output image below the MTU on the interface is now 9216. I then noticed that there was no longer a qos-group 1 enabled on the interface. I was concerned about this because qos-group 1 is for FCoE traffic and we are using FCoE mulithop from our UCS Fabric Interconnects.

image

I check the ipqos using the command “show run ipqos” and noticed that the fcoe-default-nq-policy policy map was no longer enabled on the system qos.

image

This made now made since and I didn’t think about it when I applied the new jumbo-MTU policy. System qos can only have a single policy from each type applied to it at any given time.

To get around this I created a new policy-map named fcoe-with-jumbo-mtu. Here is the configuration for it.

image

Once I applied the new policy map to the system qos the output of “show queuing interface e1/20” looked correct.

image

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2 thoughts on “Nexus 5500 FCoE and Jumbo MTU

  1. Richard ponuda tokarski stroj otvoreno primijeniti ubiti.
    Drugi tumacenje snova zgrada pukne brzo.Sanovnik sanjati
    putovanje potjera iskustvo sanjati obalu. Bobica koristan klik
    opetovano organizovati kao. Njihovo sanjati fudbalsku utakmicu dok nikad.
    Sanovnik tumacenje snova jezero donijeti isušivati sanjati eksplozije.

  2. Reblogged this on Mailave! and commented:
    Since Cisco documentation doesn’t cover the situation when you have FCoE enabled ports , I was about to write my own version of “Enabling Jumbo Frame on Nexus 5500 Platform while having FCoE enabled ports” but noticed that my good friend Jeremy has already published a great post here.

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