Nexus 3548 Jumbo Frames

[flyshoo]

Hello Networkers,

I have a question about the Nexus 3548 handling of Jumbo Frames.  Why does the interface command return the value mtu 1500 when you run sh int e1/x but jumbo frames continue to work on the interface?  I did what was required to get the Jumbo frames to work and can verify when I run "show queuing interface ether 1/x | grep MTU" it returns "HW MTU: 9216 (9216 configured)".

Also ping with an mtu 9000 works as it should.

Asking because it confuses people when they look at the output from show interface or CDP in VMWare console.  I would like an answer for them next time someone asks.

Ethernet1/8 is up
Dedicated Interface
Hardware: 100/1000/10000 Ethernet, address: 7070.8b3d.214f (bia 7070.8b3d.214f
Description: phx-esx-01
MTU 1500 bytes, BW 10000000 Kbit, DLY 10 usec

show queuing interface ether 1/8 | grep MTU
HW MTU: 9216 (9216 configured)

Thanks,

Fly

[acampbell · Accepted solution]

Hi,

Have a read at this from the nexus 3548 config guide.

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus3548/sw/interfaces/b_N3548_Interfaces_Config_503_A1/b_N3548_Interfaces_Config_503_A1_chapter_01.html#con_1266623

"About MTU Configuration
The Cisco Nexus device switch does not fragment frames. As a result, the switch cannot have two ports in the same Layer 2 domain with different maximum transmission units (MTUs). A per-physical Ethernet interface MTU is not supported. Instead, the MTU is set according to the QoS classes. You modify the MTU by setting class and policy maps.

Note
When you show the interface settings, a default MTU of 1500 is displayed for physical Ethernet interfaces."

[flyshoo]

Thank you this is very helpful.  I have something to show people when they ask.