MTU Size

I have Cisco Nexus 5672 switch.
I have configured port channel say Po 20 & i have associated this with the 2 physical interface Eth1/1 & Eth1/2

I want to set the MTU size on these interfaces to be 1700 bytes.
Let me know how to do it. Is MTU applied on the port channel interface or via globally.
I want to set it to only to these interfaces.
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SrikantRajeevAsked:
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artyom39Commented:
I don't think it's supported change mtu per interface, in order to change mtu size globally it's should be:

system mtu mtusize
SrikantRajeevAuthor Commented:
Thanks.

But in this case i have my Nexus 5K uplink connected to Nexus 7K device.
The uplink on my 5K is configured to be 1600 but at Nexus 7K interface it is configured to be 1500.
Will it create any issue.
JustInCaseCommented:
In post that artyom39 gave is the way to define MTU size, but it will not be used if it is not configured by class and policy maps.
MTU

The Cisco Nexus device is a Layer 2 switch, and it does not support packet fragmentation. A maximum transmission unit (MTU) configuration mismatch between ingress and egress interfaces may result in packets being truncated.

When configuring MTU, follow these guidelines:

    MTU is specified per system class. The system class allows a different MTU for each class of traffic but they must be consistent on all ports across the entire switch. You cannot configure MTU on the interfaces.
    Fibre Channel and FCoE payload MTU is 2158 bytes across the switch. As a result, the rxbufsize for Fibre Channel interfaces is fixed at 2158 bytes. If the Cisco Nexus device receives an rxbufsize from a peer that is different than 2158 bytes, it will fail the exchange of link parameters (ELP) negotiation and not bring the link up.
    Enter the system jumbomtu command to define the upper bound of any MTU in the system. The system jumbo MTU has a default value of 9216 bytes. The minimum MTU is 2158 bytes and the maximum MTU is 9216 bytes.
    The system class MTU sets the MTU for all packets in the class. The system class MTU cannot be configured larger than the global jumbo MTU.
    The FCoE system class (for Fibre Channel and FCoE traffic) has a default MTU of 2158 bytes. This value cannot be modified.
    The switch sends the MTU configuration to network adapters that support DCBX.
Article and configuration example
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SrikantRajeevAuthor Commented:
Thanks.
But for my below query what is the answer.

But in this case i have my Nexus 5K uplink connected to Nexus 7K device.
The uplink on my 5K is configured to be 1600 but at Nexus 7K interface it is configured to be 1500.
Will it create any issue.
JustInCaseCommented:
Most likely it create problems.
For Jumbo mtu to work properly it should be configured on all interfaces, including physical interface and vlan interface (on Nexus 7K). If you have port channel configured then it should also have jumbo mtu enabled. Make sure that all possible paths between any jumbo enabled end-points are all jumbo enabled.
Source

and I found this excellent article:
Peter Revil - definitive jumbo frames
SrikantRajeevAuthor Commented:
the reason i am enabling the MTU size as 1600 in my Nexus 5K is because i will be using VXLAN .
There will be no VXLAN between my Nexus 5K to the Nexus 7K.
VXLAN will not cross my Nexus  5k to reach Nexus 7K.
So i would like to confirm this part. Will it create any problem.
Don JohnstonInstructorCommented:
Configuring larger MTU's on the 5K is a little different than on the 7K. Where you can set the MTU per interface on the 7K's, on the 5K's in global (unfortunately).

policy-map type network-qos JUMBO_MTU
  class type network-qos class-default
    mtu 1400
!
system qos
  service-policy type network-qos JUMBO_MTU

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If you have any port channels on the 5K then you would want the same MTU on the peer switches.
SrikantRajeevAuthor Commented:
the reason i am enabling the MTU size as 1600 in my Nexus 5K is because i will be using VXLAN .
There will be no VXLAN between my Nexus 5K to the Nexus 7K.
VXLAN will not cross my Nexus  5k to reach Nexus 7K.
So i would like to confirm this part. Will it create any problem.
Don JohnstonInstructorCommented:
No, it will not create any problems to have VXLAN on the 5K and not on the 7K.

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SrikantRajeevAuthor Commented:
Thanks
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