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Enabling Jumbo Frames

Posted on 2009-12-20
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i would like to enable jumbo frames on my catalyst 2960 for my iscsi storage, it seems that there is no option to only enable jumbo frames for a specific vlan, would enabling it on the entire switch have an adverse effect on the other vlans where the end stations do not have jumbo frames enabled?
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Question by:mtatechys
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by:woolmilkporc
ID: 26091657
Hi,

as far as I know jumbo frames can always be received and processed, by any GE capable interface.

Enabling jumbo frames only means to enable sending them.

wmp




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by:mtatechys
ID: 26091914
my question is if i enable jumbo frames on the switch and i have servers/workstations etc connected to the switch that dont support jumbo frames - will there be any impact on those machines - is there anything i need to be careful with, for example say i had a sql server on the network and its NIC is configured for jumbo frames but the clients arent configured for them what would happen
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by:woolmilkporc
ID: 26091991
As I told you - any station can RECEIVE and process jumbo frames, whether enabled or not.
Only enabled stations can SEND them.
Obviously you won't see a performance gain in communications between enabled and non-enabled stations.
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by:Don Johnston
ID: 26093141
According to this document:

http://www.cisco.com/en/US/products/hw/switches/ps700/products_configuration_example09186a008010edab.shtml#c4a

"The default maximum transmission unit (MTU) size for frames received        and transmitted on all interfaces on the switch is 1500 bytes."

"You can        increase the MTU size to support jumbo frames on all Gigabit Ethernet        interfaces with the system mtu jumbo global        configuration command."

After enabling jumbo frames, you must reload the switch.

The "show system mtu" command will display if jumbo frames are enabled.
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Aaron Street earned 750 total points
ID: 26094636
You should be find when enabeling jumbo frames. most devices are self limiting so if one station cant support jumbo frams then they will nto be sent for that link. if both ends suport them and they are enabled then they will be used.

All my core switchs have jumbo frames enabables now and still most traffic is sent using the stnadard 1500 MTU size. only when servers at both ends are enababled do you see jumbo frmaes being sent
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