Cisco Nexus 3064 – Configuring Jumbo Frames

The default MTU size on a Nexus 3064 switch is 1500 bytes, the following details how to reconfigure the switch for a system wide MTU value of 9216(jumbo).

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Note: The Cisco Nexus 3000 Series switch does not fragment frames. As a result, the switch cannot have two ports in the same Layer 2 domain with different maximum transmission units (MTUs). A per-physical Ethernet interface MTU is not supported. Instead, the MTU is set according to the QoS classes. You modify the MTU by setting Class and Policy maps.
As per Cisco Documentation
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Configuring Jumbo Frames:
Begin by creating a policy-map of type network-qos named aptly in this example ‘JumboFrames’ and assign as the system-qos. (As stated above you cannot configure on a per interface level).


n3k-sw# config t
n3k-sw(config)# policy-map type network-qos ?
WORD Policy-map name (Max Size 40)
n3k-sw(config)# policy-map type network-qos JumboFrames
n3k-sw(config-pmap-nq)# class type network-qos class-default
n3k-sw(config-pmap-nq-c)# mtu 9216
n3k-sw(config-pmap-nq-c)# system qos
n3k-sw(config-sys-qos)# service-policy type network-qos ?
WORD Policy-map name (Max Size 40)
n3k-sw(config-sys-qos)# service-policy type network-qos class-default
n3k-sw(config-sys-qos)# show policy-map type network-qos
Type network-qos policy-maps
===============================
policy-map type network-qos JumboFrames
class type network-qos class-default
mtu 9216

Verification of the change can be validated by running a ‘show queuing interface’ command on one of the 3k interfaces (interface Ethernet 1/2 in this example):

n3k-sw# show queuing interface ethernet 1/2

Ethernet1/2 queuing information:
qos-group sched-type oper-bandwidth
0 WRR 100
qos-group 0
HW MTU: 9216 (9216 configured)
drop-type: drop, xon: 0, xoff: 0

If you run the ‘show interface’ command then a value of 1500 will be displayed despite the system wide change that was made:
n3k-sw# show queuing interface ethernet 1/2
Ethernet1/2 is up
Dedicated Interface
Hardware: 100/1000/10000 Ethernet
Description: 6296 2A Mgmt0
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec

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