jumbo frame question

Unanswered Question
Aug 18th, 2010


if I want enalbe jumbo frame support on cisco 6500 ios ver 12.2(33) SXI2a, what impact will occur?

and can I enable jumbo frame support only on a subnet/vlan?  specially, can I enable jumbo frame only on certain ports?

Any comments will be apprecaited

Thanks in advance


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francisco_1 Wed, 08/18/2010 - 03:38

that will depends on what cards you have installed.

post "show module"


julxu Wed, 08/18/2010 - 19:06

thanks for the reply.

I have ws-x6748-ge-tx, also ws-x6704-10ge. on cat6500 (vss).  but, I will put jumbo frame on ws-x6748-ge-tx card.

so, if I want just configure it on port only, what I need do is only configre the MTU to 9128, right?

question, since another end is a workstation, which on a cat3750 connected to other cat6500, if I enbale jumbo frame on port also on cat3750

can both talk to each other?  do I need do anything else?


julxu Wed, 08/18/2010 - 19:23

Lei Tain

thank for the url,

I have more than one machine need this jumbo frame, and they are on differenct cat6500, some of them even on layer 2 switch cat3750s.

can I just set MTU to 9126 only, can the server use jumbo frame to the client with located on other cat6500 and other cat3750s?

if not, could you please advice me what configuration I need to make them working together?

Thanks in advance


Reza Sharifi Wed, 08/18/2010 - 19:36

Hi julxu,

You can also enable jumbo frame on your 3750s.  With 6500 you can do a globally or one module at the time, but with 3750s you can only enable it globally.  Also the 3750s require a reboot in order for the jumbo frame size to take effect, so be sure to do it during on outage.



Lei Tian Wed, 08/18/2010 - 19:50

Hi julxu,

What's your 3750's model? 3750 supports 9018 bytes jumbo frame on GE port, 3750-E supports 9216 bytes on GE port. You need to make sure all the ports along the path support the jumbo frame size, otherwise packet will be fragment and forward by software.If you want the server-client traffic benefit from jumbo frame, then I think you both NIC need to support jumbo frame as well.


Lei Tian

julxu Wed, 08/18/2010 - 21:11

hi everyone

thanks for all the emails.

last qeustion, since it involves large packets everywhere, will I have furture perfermance problem? thoughtout problems? or other problems which will interrupt our services? specially video/voice facility which all linked to same cat6500s/cat3750s?

if so, do I have some work around to fix it?

Many Regads


Lei Tian Thu, 08/19/2010 - 08:20

Hi julxu,

If there is fragmentation caused by MTU mismatch, then it might impact switch performance and affect other services. Otherwise, it is fine.


Lei Tian


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