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Joshua Engels

How to: Enable Jumbo Frames on single VLAN (Nexus 5548UP)

Hey guys,

We are currently using two Nexus 5548UP's as our Datacenter Network Core.  I have a pretty simple objective:  I would like to enable Jumbo Frames on a single VLAN only(VLAN 65).  This VLAN is used strictly for backups.  I do not want to enable Jumbo Frames on the other VLANs(VLANs 1-10).  Im not sure what the best way to do this is.....or if it is even possible but I am hoping to get some configuration examples. 

Hopefully this is a pretty simple configuration.  Thanks for your help everyone


Reza Sharifi
Hall of Fame Expert

Hi Josh,

On the 5k, you would need to enable it for the entire switch (link below) using a policy map. You can't enable it per layer-2 vlan.  On the 7k, you can enable it per interface and per layer-3 vlan.



Suppose if we have an access switch which uplinked through a trunk link to a core switch and this core switch is connected and internet router.

Now, if a PC is connected to the switch and sends jumbo frames, how exactly would it work when both switches are configured for Jumbo Frame and router does not support it?


If the core switch is connected to a router and you have jumbo on one side of the link and standard 1500 MTU on the other side, that is MTU mismatch. it will not work.  Now if you have jumbo on the switch side and jumbo on the router and than the router connects to another router using 1500 MTU, the packet coming from the switch out to the router is jumbo and than the router will fragment the packet before sending it to the next router



I have seen many Scenarios deploying N5K (FCoE based) uplinked to Core switches (non Nexus switches) and Core switches connected to Internet facing routers. Now if one enables JF on N5K, then what is the best way to handle such situations?

One would not like to configure JF on internet facing router.


Reza Sharifi
Hall of Fame Expert


Does your 5k have a layer-3  card installed?

I am wondering if you have one you can apply jumbo to the physical interface


Joshua Engels

(yes we do have a layer 3 card)

Hey Guys,

Here is the answer to how we configured Jumbo Frames for a only a specific vlan.  We used QoS.  Below is our config.  I am hoping I can get some feedback on doing it this way.  All comments welcome.

ip access-list JUMBO_TRAFFIC

  permit ip any

  permit ip any

  permit ip any

  permit ip any

class-map type qos match-any VLAN_QOS

     match access-group name JUMBO_TRAFFIC

policy-map type qos VLAN_QOS_POLICY

   class type qos VLAN_QOS

     set qos-group 5

class-map type network-qos JUMBO_FRAMES

     match qos-group 5

policy-map type network-qos VLAN_NETWORK_POLICY

   class type network-qos JUMBO_FRAMES

     mtu 9000

   class type network-qos class-fcoe

     pause no-drop

     mtu 2158

   class type network-qos class-default

class-map type queuing QUEUING_CLASS

     match qos-group 5

policy-map type queuing QUEUING_POLICY

class type queuing QUEUING_CLASS

bandwidth percent 50

class type queuing class-default

bandwidth percent 50

system qos

service-policy type network-qos VLAN_NETWORK_POLICY

service-policy type qos input VLAN_QOS_POLICY

service-policy type queuing output QUEUING_POLICY

service-policy type queuing input QUEUING_POLICY

Hi Joshua ,

its been long time since you posted this ,

but did you manage to apply this config and got the JumboFrames on a Single Vlan ?

( ps - was it a vlans crossing other switches as well so you needed to also change MTU on them ? )