MTU

Chris_Bay · December 16, 2017, 3:59am

ive noticed MTU defined larger than 1500 is not working correctly, and slightly backwards. we had set an MTU of 1528 in our PTP epmp radios, matching our switches. I can't ping them with anything larget than 1484. if i turn it up to 1700, i can't hit them with anything larger than 1472. if the radios is at the default MTU of 1500, i can ping them with 1500?

Fedor · December 16, 2017, 9:14am

Hi Chris,

Thank you for letting us know.

Is it with 3.5.1 Release, right?

Thank you.

Chris_Bay · December 16, 2017, 1:22pm

Im on 3.5, ill repeat the test on 3.5.1 shortly

Thank you!

Fedor · December 20, 2017, 11:47am

Hi Chris,

We have tested MTU on 3.5.1 Release with 1700 bytes and 1600 bytes configured on ePMP bridge and it works as expected.

Please make sure appropriate MTU is applied properly on your switches behind ePMP bridge.

Thank you.

toto · December 21, 2017, 11:02pm

I confirm, there are no problems with MTU, I work with all my equipment at 1600 without problems …

Chris_Bay · December 21, 2017, 11:22pm

It works fine through the bridge, its hitting the radios themselves is when i noticed it.

Fedor · December 22, 2017, 2:35pm

Chris,

MTU is applied on interface.
So there is no difference between case when traffic is passing through the bridge or you are just trying to ping it or get http connection.

Thank you.

Douglas_Generous · December 23, 2017, 3:55pm

There is a big difference in the MTU passed over the bridge versus the MTU that the radio its self responds to. We have to use very large MTU settings between towers (we set to 1700) which works tower router to tower router. But in connecting to the web page or ssh into the radio and 1500 is the best you can do. This is not really a problem for us as the MTU across the bridge is what is important.

We have noticed this difference in how the MTU is used since release 2.1

Fedor · December 25, 2017, 10:25am

Thank you for update.
We will doublecheck it and revert to you.

Thank you.

Fedor · January 1, 2018, 1:24pm

Hi Douglas,

Just to exclude any type of misunderstanding could you please confirm you cannot reach web interface of ePMP device with Ethernet MT configured with value higher 1500 ?
We have tested and it works well for us for both scenarios when traffic is passing through the bridge and when you are getting web or ssh access to device directly.
As I mentioned before Ethernet MTU is supposed to be applied on Ethernet interface. Wireless interface MTU is always 1708.
If you could show us where Ethernet MTU misbehaves we would be really grateful and will fix it asap.

Thank you.

Nerea1 · October 9, 2018, 3:03pm

Good evening! MTU above 1700 provides for the passage of non-fragmented packets?