Oversized or undersized packets detected

[TheAlchemist]

Below alert showed up on Meraki dashboard >Alerts>Device Health. What would this refer to? and could it lead to the link /connection going down ?

"Oversized or undersized packets detected."

"Detecting a very high proportion of oversized or undersized packets on SWXX"

[alemabrahao]

It's probably about the MTU.

https://documentation.meraki.com/General_Administration/Tools_and_Troubleshooting/Troubleshooting_MT...

[BlakeRichardson]

Agree it's likely a random device has an incorrect MTU. Does the dashboard show you which switch port this is happening on so that you can narrow it down to what device? 

[TheAlchemist]

Yes, on clicking the message on alert it takes to the Switch and highlights the port.

[TheAlchemist]

Switch settings show MTU size set of 9578 (Jumbo frames) by default. As per the instructions you shared in the link, I cannot ping any public DNS over MTU 1472. Think Public internet does not support Jumbo frames so MX would be limited by max 1500 but withing MS switches in our network, Jumbo frames should pass through? I think.

[alemabrahao]

Probably, but remember to read between the lines of the documentation.

Note: Please contact Meraki support to modify the MTU size on the WAN link of the MX. The MX does not support Jumbo frames so the MTU cannot be adjusted above 1500. The MTU value on the LAN-side of the MX is also 1500.