MS425 MTU Size

[RWelch]

The dashboard indicates MS425 is limited by hardware to Max MTU size of 9394. 

The MS425 Overview and Specifications page shows Max MTU size of 9416.
https://documentation.meraki.com/MS/MS_Overview_and_Specifications/MS425_Overview_and_Specifications

I have two MS425s at separate locations.  Anyone else encounter this?  

Thank you.

[PhilipDAth]

I've never run into it ... but I have never tried an MTU of over 9000.

[GIdenJoe · Accepted solution]

An ethernet header with 802.1Q tag is 22 bytes long.
9416 - 22 = 9394 bytes.

So the specifications document includes the bytes needed for the ethernet header itself.
So technically they are correct but indeed MTU is usually the max payload size.
I would call this an error in the documentation but one I can understand why. 🙂

[RWelch]

Thank you @GIdenJoe.  I wasn’t changing the MTU size rather setting STP root priority bridge when I noticed the dashboard notification on the page when doing so.

[GIdenJoe]

No problem 😉
Btw Catalyst based switches have a maximum MTU of 9198 which is a tad lower.
In my personal view, the only reason to actually need higher MTU is in fabric networks, what Meraki managed switches do not currently support or high end storage networking.
All the rest uses the standard 1500 MTU anyways.

[Brash]

One of my biggest frustrations is that switches vary so much between vendors (or even just between OS's) as to whether they require full frame size or payload size when setting MTU.

[Tony-Sydney-AU]

Hello @RWelch ,

Thanks for bringing this up.

@GIdenJoe is correct. I'm working with Internal teams on adding this info.

[RaphaelL]

Hi ,

That info is also present on that page : https://documentation.meraki.com/MS/Other_Topics/Switch_Settings

Would also double check that : The maximum MTU on MS390/C9300/C9300X/C9300L switches is 9198 bytes

[Tony-Sydney-AU]

Good news, Everyone!

Both articles are now updated!

MS425 Overview and Specifications has a clarification about MTU value in the Dashboard.

Switch Settings has a new and improved MTU Settings section covering all.

Thank you, @RaphaelL ! Yes, I realised that while working in first article. This is why it took me longer than usual to publish updates.