Jumbo frame

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Jul 27th, 2009
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I have enable jumbo frame in our 6500 in gi2/2. The mtu shows 9216 under the swtich port configuration. Do I aslo need to enable jumbo frame in the server NIC that connect to port gi2/2. If I don't do that, is there any impact?


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jbrenesj Mon, 07/27/2009 - 09:33
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If there is any large frame going out g2/2 towards your server, the switch will send it but the server will drop it.

It also happens the other way around if the server supports larger frames and the switch don't.

If you are not moving any frames larger than the default 1500 bytes then there is no problem but in that case why enabling jumbo frame support on the switch interface?

sightlay8 Mon, 07/27/2009 - 10:02
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So, will it hurt to enable jumbo frame in Cisco switch even I have no jmbo frame send in and out?

jbrenesj Mon, 07/27/2009 - 10:09
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It won't matter to enable it if you are not using large grames but if you are then the switch will forward/receive them just fine but you end devices (servers) may drop them

sightlay8 Tue, 07/28/2009 - 11:25
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I enabled jumbo frame in every port, it hows mtu 9216 in every port. But when I showed vlan, I saw the vlan mtu is still 1500. Do I also need to change the Vlan MTU, or the vlan mtu has no actual effect.


Giuseppe Larosa Mon, 07/27/2009 - 10:48
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Hello Tak,

>> o, will it hurt to enable jumbo frame in Cisco switch even I have no jmbo frame send in and out?

There is always a price to pay for everything you enable on a device.

In the case of jumbo frames the port buffers can be reorganized to be able to handle so big frames so you may get shorter input and output buffers that in some linecards can have an impact.

Hope to help


dabels Tue, 07/28/2009 - 12:28
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also remember if you HAVE jumbo frames running in your network you will need have jumbo enabled all the way thru and not just on the end station port.

prakadeesh Wed, 07/29/2009 - 01:52
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when I implemented Jumbo frames, i had to implement MTU changes at both the VLAN level as well as port level. Since I have a trunk running to another switch I had to change the port channel setting MTU too. But as a best practice I was adviced that jumbo frame traffic be kept on separate vlan.


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