MTU

Answered Question
Aug 25th, 2008

Hi,

Is there a difference between interface MTU and IP MTU ?

Thanks, birdy

Correct Answer by Joseph W. Doherty about 8 years 6 months ago

Yes, they are different. IP MTU only applies to IP packets.

"Note Changing the MTU value (with the mtu interface configuration command) can affect the IP MTU value. If the current IP MTU value is the same as the MTU value, and you change the MTU value, the IP MTU value will be modified automatically to match the new MTU. However, the reverse is not true; changing the IP MTU value has no effect on the value for the mtu command."

Correct Answer by alexander76 about 8 years 6 months ago

Hi,

you can use the command lookup tool to solve your problem ;)

ip mtu (source: command lookup tool)

To set the maximum transmission unit (MTU) size of IP packets sent on an interface, use the ip mtu command in interface configuration mode. To restore the default MTU size, use the no form of this command.

ip mtu bytes

no ip mtu

Syntax Description

bytes

MTU in bytes.

Defaults

Minimum is 128 bytes; maximum depends on the interface medium.

Command Modes

Interface configuration (config-if)

Command History

Release Modification

10.0

This command was introduced.

12.2(33)SRA

This command was integrated into Cisco IOS Release 12.2(33)SRA.

12.2SX

This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Usage Guidelines

If an IP packet exceeds the MTU set for the interface, the Cisco IOS software will fragment it.

All devices on a physical medium must have the same protocol MTU in order to operate.

Greetz from Germany ;)

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Overall Rating: 3.3 (3 ratings)
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faisal_ghaus Mon, 08/25/2008 - 04:06

HI

The hardware MTU configured with the mtu interface configuration command

The IP MTU configured with the ip mtu interface configuration command

The MPLS MTU configured with the mpls mtu interface configuration command

Hope this help

birdy Mon, 08/25/2008 - 04:59

Hi,

Thanks for yr reply.

I am not refering to the command but is asking what is the difference between IP MTU and interface MTU ?

Is the IP MTU size always the same as the interface MTU size ?

Regards

Correct Answer
alexander76 Mon, 08/25/2008 - 06:56

Hi,

you can use the command lookup tool to solve your problem ;)

ip mtu (source: command lookup tool)

To set the maximum transmission unit (MTU) size of IP packets sent on an interface, use the ip mtu command in interface configuration mode. To restore the default MTU size, use the no form of this command.

ip mtu bytes

no ip mtu

Syntax Description

bytes

MTU in bytes.

Defaults

Minimum is 128 bytes; maximum depends on the interface medium.

Command Modes

Interface configuration (config-if)

Command History

Release Modification

10.0

This command was introduced.

12.2(33)SRA

This command was integrated into Cisco IOS Release 12.2(33)SRA.

12.2SX

This command is supported in the Cisco IOS Release 12.2SX train. Support in a specific 12.2SX release of this train depends on your feature set, platform, and platform hardware.

Usage Guidelines

If an IP packet exceeds the MTU set for the interface, the Cisco IOS software will fragment it.

All devices on a physical medium must have the same protocol MTU in order to operate.

Greetz from Germany ;)

Correct Answer
Joseph W. Doherty Mon, 08/25/2008 - 08:59

Yes, they are different. IP MTU only applies to IP packets.

"Note Changing the MTU value (with the mtu interface configuration command) can affect the IP MTU value. If the current IP MTU value is the same as the MTU value, and you change the MTU value, the IP MTU value will be modified automatically to match the new MTU. However, the reverse is not true; changing the IP MTU value has no effect on the value for the mtu command."

birdy Mon, 08/25/2008 - 10:42

Hi All,

Thanks for your explanation.

Now it is much clearer.

Thanks again

birdy

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