default system mtu on 9606 switches

[carl_townshend]

Hi All

We have noticed an issue on our new 9606 switches, the system mtu appears to be 9216, and all the layer 2 and 3 svi's seem to be on 9216.

First of all, is this the default?

Second, will this cause many issues if the switches that plug into it that are running 1500?

Cheers

[balaji.bandi]

As  per i know the default is 1500 on Cat 9K, until any New IOS XE setup as part of SD-Access.

You can do per port   MTU, where the device connected backward with 1500, you can setup per port basis.

is this part of SD-Access ? check the default requirement to be MTU 9XXX

[carl_townshend]

Hi, no it is not for SD Access.

I will need to change the system mtu back to 1500

Can I then set on individual interfaces the mtu to 9216?

cheers

[balaji.bandi]

Follow below guide Lines, you can do system MTU 1500 or 9216 - also you can configure per port also.

My suggestionis keep system MTU 9216 and per port you can customise based on requirement.

If the Per-Port MTU is disabled, the MTU for the port will revert to the system MTU value.

To override system MTU values on routed interfaces, configure protocol-specific MTU under each routed interface

[Joseph W. Doherty]

Like Balaji, I too believe the default MTU should be 1500.

As to connecting devices to ports which can process jumbo Ethernet frames, but that device doesn't, it shouldn't cause any issues unless some other device is trying to interact with a "standard" Ethernet frame size device using jumbo frames.

I.e. jumbo Ethernet interfaces can process standard Ethernet frames w/o issue but the converse may be a problem.

PS:

BTW, in the above I'm just referring to L2.  L3 works a bit differently when MTU changes.

[j.stirgus68910]

I have similar issue on a 9300. If I change the system mtu to 9000, do I have to reload the switch for it to take affect?