3750X Jumbo Frames

[Julian Regel]

Hi

I've got a Cisco 3750X stack pair and "show system mtu" reports:

System MTU size is 1500 bytes

System Jumbo MTU size is 9000 bytes

Routing MTU size is 1500 bytes

Everything I've read suggests that this means I've got Jumbo Frames enabled. However, there is nothing in my running config to say that this has been set (although I've read that the "system mtu jumbo 9000" won't appear anyway, but no explanation as to why this is the case).

Please could someone confirm if my understanding is correct? We don't currently have Jumbo Frames setup on our hosts and I don't want to enable it only to find I missed something on the switch.

Many thanks!

JR

[Reza Sharifi]

Hi,

Your understanding is correct.  It does not show it in the running config, but the interface correctly shows that jumbo frame is enabled

Have a look:

3750-Switch#sh run | inc mtu

system mtu routing 1500

3750-Switch#sh interfaces gi1/0/1

GigabitEthernet1/0/1 is up, line protocol is up (connected)

  Hardware is Gigabit Ethernet, address is 001b.5400.3381 (bia 001b.5400.3381)

  MTU 9198 bytes, BW 100000 Kbit, DLY 100 usec,

     reliability 255/255, txload 1/255, rxload 1/255

HTH

[Julian Regel]

Thanks Reza

I've just checked by running "sh int" and can see that MTU is set to 9000, so that looks conclusive.

Just curious why your output shows 9198 bytes but mine shows 9000. Any ideas?

Thanks