policy-map type network-qos mtu confusion

[cmturner20]

Have a question in regards to setting this to 9216 instead of the default 1500:

class type network-qos c-8q-nq1
mtu 1500
class type network-qos c-8q-nq2
mtu 9216
class type network-qos c-8q-nq3
mtu 1500
class type network-qos c-8q-nq4
mtu 1500
class type network-qos c-8q-nq5
mtu 9216
class type network-qos c-8q-nq6
mtu 1500
class type network-qos c-8q-nq7
mtu 9216

Does this have any effect on network performance if I set all the class types to 9216? I do have some 9k traffic but not on every vlan/interface. From the doco it says:

"• When enabling jumbo MTU, the default network QoS policy can support jumbo frames. Under the
network QoS policy, the MTU is used only for buffer carving when no-drop classes are configured. No
additional MTU adjustments are required under the network QoS policy to support jumbo MTU."

So setting it all to 9216 should have no real effect if no-drop is not used correct? Am I better leaving them at 1500 or 9216? 

Thanks

[williameva869]

Not so sure on this. But surely someone will help us on this issue. Also, one of the options is using AI step-by-step guide to get an answer.

[M02@rt37 · Accepted solution]

Hello @cmturner20 

No, set all to 9216 will not degrade performance if you’re not using no-drop.

And yes, it is generaly safe and even recommended when you have any jumbo traffic.

Only tune per-class MTU if you want t9 optimize buffers for lossless trafic.