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Community Member

Nexus 7000 - Configuring L2 Jumbomtu

Hello,

I'd like to know if applying the below commands to configure the L2 MTU size to a size larger than the defual size(1500) would have any disruptive effects on the production switch.

Thanks in advance.

Best, ~sK 

o configure the system jumbo maximum transmission unit (MTU) size for Layer 2 interfaces, use the system jumbomtu command.

system jumbomtu size

Syntax Description

size

Even number between 1500 and 9216.

Defaults

The system jumbo MTU default size is 9216 bytes and the interface default MTU is 1500 bytes.

Command Modes

Global configuration mode

Supported User Roles

network-admin
vdc-admin

Command History

Release

Modification

4.0

This command was introduced.


Usage Guidelines

Use the system jumbomtu command to specify the MTU size for Layer 2 interfaces. The range is from 1500 to 9216.

The physical level uses an unchangeable bandwidth of 1 GB.

This command does not require a license.

Examples

This example shows how to configure the system jumbo MTU as 8000 bytes and how to change the MTU specification for an interface that was configured with the previous jumbo MTU size:

switch# config t 

switch(config)# system jumbomtu 8000

switch(config)# show running-config

switch(config)# interface ethernet 2/2

switch(config-if)# switchport

switch(config-if)# mtu 4608
1 ACCEPTED SOLUTION

Accepted Solutions

Re:Nexus 7000 - Configuring L2 Jumbomtu

Hello,

Glad to know there were no problems bud.

Now the explanation.

When changing the mtu to a lower value you got to be careful as there might be hosts that will send traffic over the setting configured in ur interface.

If this happens 2 things could happen and both of them depending on whether the host send the traffic with the df bit set on the IP header.
Fragment the packet if df not set
Send a fragmentation needed icmp packet if df is set.

If you change the value to a higher level no problem will be shown.

Remember that a mismatch within mtu interface values on OSPF will never allow u to build a ospf adjacency.


If u do not have any other question please mark it as resolved

Sent from Cisco Technical Support Android App

Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2xCCNP, JNCIP-SEC
3 REPLIES
Community Member

Nexus 7000 - Configuring L2 Jumbomtu

Applied the commands. No interruptions occured.

Thanks!

Re:Nexus 7000 - Configuring L2 Jumbomtu

Hello,

Glad to know there were no problems bud.

Now the explanation.

When changing the mtu to a lower value you got to be careful as there might be hosts that will send traffic over the setting configured in ur interface.

If this happens 2 things could happen and both of them depending on whether the host send the traffic with the df bit set on the IP header.
Fragment the packet if df not set
Send a fragmentation needed icmp packet if df is set.

If you change the value to a higher level no problem will be shown.

Remember that a mismatch within mtu interface values on OSPF will never allow u to build a ospf adjacency.


If u do not have any other question please mark it as resolved

Sent from Cisco Technical Support Android App

Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2xCCNP, JNCIP-SEC
Community Member

Nexus 7000 - Configuring L2 Jumbomtu

Thanks, Julio!

I appreciate that respose.

Best, ~sK

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