MTU size

[kamrannaseem1]

Hello,

Is there any way to check the optimum MTU size on cisco routers ?

Many thanks.

[Julio E. Moisa]

Hi

Usually the used MTU is 1500 bytes, but if you have 10G ports you could modify the MTU to support Jumbo MTU (9216 bytes).

Hope it is useful

:-)

[Hector Gustavo Serrano Gutierrez]

Some platforms also support Jumbo Frames on GigabitEthernet interfaces.

If interested, you can verify with:

Router(config)#int gig0/0/0
Router(config-if)#mtu ?
  <1500-9216>  MTU size in bytes

Just fyi, this output was taken from a ISR4451-X Router.

[kamrannaseem1]

Hello,

What I meant was how to check the MTU size already configured on the router ?

many thanks.

[Julio E. Moisa]

Hi

Try with:

show system mtu

[kamrannaseem1]

Hello,

No this command doesn't work.

[Julio E. Moisa]

hi

What is your device model?

Other way is:

show interfaces | i MTU  (you can specify the interface to check)

[kamrannaseem1]

Hello,

Cisco 2901

[Julio E. Moisa]

You can use:

show interfaces mtu

[lokesh lawania]

This command does not work on cisco

[abdelmoutalib taif]

this has caused me some headaches, because without one of those two things configured, there is a lot of packet fragmentation :)

[Deepak Kumar]

Hi,

To check L3 MTU on an interface issue sh ip int {if-number}. To check L2 MTU issue sh int {if-number} command. 

Regards,

Deepak Kumar

[Vishnu Vardhan S]

Hi !!

For Cisco Routers use below command :

#show interface fa0/0 | include MTU

On a normal scenario, the MTU would be 1500 bytes. Normally an MTU includes the size of Payload, IP, and TCP header. 

Normally Payload takes 1460 bytes and 20 bytes for IP and 20 bytes for TCP.

Now talking about the Cisco Switch 2960, normally switch does not support MTU on an interface basis. 

Checkout the below link too.

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960/software/release/15-2_2_e/configuration/guide/b_1522e_2960_2960c_2960s_2960sf_2960p_cg/b_1522e_2960_2960c_2960s_2960sf_2960p_cg_chapter_01001.html

If you are running latest IOS then "#show system MTU" should work

Thanks,

Vishnu @networkchef

[conradpaule2]

the commands work and C2960G will run Jumbo Frames on IOS version 15.01(1)SE1