Michael and Jacob,

Thanks for the replies, appreciated. The Cisco 3850s displaying correctly gives me hope might be able to get this going.
Michael, does the 3850 show the 9216 as the MTU size when you do a show interface? With Jumbo working here, my interfaces still show 1500. I will have to try a few more things on the bench see if I can get it going.

On the Cisco models I am seeing the problem displaying the wrong MTU:
 N3KC3172TQ10GT running 7.0(3)I2(2d)
 2960X running 15.2(2)E5
 2960S running 15.0(2)SE10
The N3K are setup for Jumbo MTU using QoS classes, cuts from Cisco documentation for the N3K:
A per-physical Ethernet interface MTU is no supported. Instead, the MTU is set according to the QoS classes.
When you show the interface settings, a default MTU of 1500 is displayed for physical Ethernet interfaces.

On our 3K models:
policy-map type network-qos jumbo
  class type network-qos class-default
    mtu 9216
system qos
  service-policy type network-qos jumbo
 exit


On our 29xx models:
Can raise the jumbo MTU to a maximum of 9198 bytes on 2960S and 2960X switches
Switch(config)# system mtu jumbo 9198
Changes to the system jumbo MTU will not take effect until the next reload is done

Note that it is necessary to reload the switch in order for the new MTU to take effect.
Note that the MTU setting does not appear in the running or startup configuration;
this is important to remember when replicating configurations or replacing switches.
Remember to verify that the new jumbo MTU has taken effect after a reload:
Switch# show system mtu
System MTU size is 1500 bytes
System Jumbo MTU size is 9000 bytes
System Alternate MTU size is 1500 bytes
Routing MTU size is 1500 bytes

thanks!
jim

On 4/26/2017 6:24 AM, Michael wrote:
We have Cisco 3850s with jumbo frames (that show correctly in Observium).

By chance, have you restarted your switches since configuring "system mtu 9216"?  It doesn't take effect until a reload, but will still show you the new values in running config etc.

Cheers,

Michael






On 26 Apr 2017, at 12:21 am, Jim Glassford <jmglass@iup.edu> wrote:

Hi,

No luck trying to review the Observium Archives see if this was asked before, getting a Not Found off the web link.

Running Observium 17.3.8438 (stable), question on MTU size on Cisco interfaces.
On our HP ProCurve switches with Jumbo enabled, all displays correctly, see MTU as 9216 on the interfaces as expected.
On our Cisco models with Jumbo enabled, MTU shows 1500 on Average Packet Size graph. I believe this is due to Cisco interfaces showing the MTU as 1500 even when Jumbo frames are enabled and are passing Jumbo on the switch interfaces. Seeing this on both Cisco models 2960s and 3K the Average Packet Size found to be 1500.
Any chance someone have a work around for this Cisco problem, able to set the MTU up to 9216 for the interfaces?

Appreciated!
Jim



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