Enable Jumbo Frame function of Cisco Nexus 5000 and 7000

An autumn view of Taipei Campus of National Taipei University (NTPU).

For Data Center networking, and in most of the cases, jumbo frames should be enabled. However, Jumbo frame feature is not enabled by default. So the next question would be "How to enable them in Cisco's Data Center switches such as Nexus 5000 and Nexus 7000 families"?

The answer is in this page on Cisco's official site.

[Nexus 5000]

!--- You can enable the Jumbo MTU 
!--- for the whole switch by setting the MTU 
!--- to its maximum size (9216 bytes) in 
!--- the policy map for the default 
!--- Ethernet system class (class-default).

switch(config)#policy-map type network-qos jumbo
switch(config-pmap-nq)#class type network-qos class-default
switch(config-pmap-c-nq)#mtu 9216
switch(config-pmap-c-nq)#exit
switch(config-pmap-nq)#exit
switch(config)#system qos
switch(config-sys-qos)#service-policy type network-qos jumbo

That is, we have to enable jumbo frame feature by configure this inside a system QoS policy map and activate it by "system qos/service-policy" command.

In addition, Jumbo Frame is enabled per system. We cannot configure individual interfaces with different jumbo frame sizes.

[Nexus 7000]

!--- Set the MTU to its maximum  
!--- size (9216 bytes) in order  
!--- to enable the Jumbo MTU
!--- for the whole switch. 


switch(config)#system jumbomtu 9216


!--- Set the MTU specification for an interface.

switch(config)#interface ethernet x/x


!--- By default, Cisco NX-OS configures Layer 3 parameters.
In order to configure Layer 2 parameters, use this command.

switch(config-if)#switchport

switch(config-if)#mtu 9216
switch(config-if)#exit

That is, we configure it per interface at interface configuration level.

In addition, for Layer 3 interfaces, command "system jumbomtu 9216" is already enough. For Layer 2 interfaces, we have to still add interface command "mtu 9216" to enable Jumbo Frame at Layer 2 level.

[Reference]

• Configuration of Jumbo MTU on Nexus 5000 and 7000 Series