Jumbo frames on a single port on a Catalyst 3850 switch

Hello - can a single port be set to jumbo frames on a Catalyst 3850 switch? If not, will setting it globally affect other ports where the client is not capable of Jumbo frames and needs a 1500 MTU?
Damian GardnerIT AdminAsked:
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atlas_shudderedSr. Network EngineerCommented:
Jumbo processing of frames is a global setting and not able to be set to individual ports.  Enabling the processing of jumbos globally enables the switch and ASICs to handle the added frame size up to the 9600 mark but does not limit forwarding to only jumbos.  Normal framing will continue to operate as normal.  One thing that you will want to do when enabling jumbos is to monitor your switch mem usage and port utilization a little closely as jumbos will consume more resources as processes and can lead to negative performance in shorter periods of time.  Other than that, you're good to go global.

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Damian GardnerIT AdminAuthor Commented:
Great.  that's what I wanted to hear.  thank you!
Damian GardnerIT AdminAuthor Commented:
Atlas - can I ask one more question?  I've noticed on one of my switch stacks (my older Cat 3750) that in spite of all the interfaces being set to MTU 9000, the VLAN is only 1500.  I should set the VLAN up to 9000, correct?
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atlas_shudderedSr. Network EngineerCommented:
Yes, otherwise you will drop frames in traversal
Damian GardnerIT AdminAuthor Commented:
ok.  is the command to do that as follows?

switchport mode access
switchport access vlan mtu 9000?
atlas_shudderedSr. Network EngineerCommented:
To set:

3750(config)# system mtu jumbo 9000
3750(config)# exit
3750# reload

Open in new window

To confirm:

Switch# show system mtu
System MTU size is 1546 bytes
System Jumbo MTU size is 9000 bytes

Open in new window

Issuing the reload command will reload the switch/stack.  The changes will not take affect until after reload.  Practice due caution when reloading on production equipment.

Hope it all helps.
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