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MTU setting on Cisco switch

Posted on 2014-09-08
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Last Modified: 2014-09-11
I have a Cisco 3560G switch connecting to a Cisco 3750x switch via fiber 1Gbps.
On the 3560g I can configure jumbo fames to 9000 bytes and on the 3750x I can configure jumbo frames to 9198 bytes.
Will this create a problem when on one switch it has 9000 bytes jumbo frames and the other one 9198 bytes.
Or must I configure both switches to 9000 bytes.
Please advice on this
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Question by:ciscosupp
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Ashok Dewan earned 167 total points
ID: 40310847
Yes, MTU value should be same for neighbor devices to communicate properly.

you can find the correct MTU for your configuration you must run a simple DOS Ping test. You will simply send out ping requests and progressively lower your packet size until the packet no longer needs to be fragmented. Please reference the following command.

ping www.tp-link.com -f -l xxxx

f for don't fragment the packet
l for setting buffer size
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Expert Comment

by:Natty Greg
ID: 40311256
size must be the same and be supported on each end
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Author Comment

by:ciscosupp
ID: 40311300
so can my uplinks be 9000 bytes and port for end user be  still be 1500 bytes without getting any problems
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Assisted Solution

by:Craig Beck
Craig Beck earned 333 total points
ID: 40315152
Yes, the uplinks can have a larger MTU than the user ports, but it shouldn't be smaller than user ports.
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Author Comment

by:ciscosupp
ID: 40315180
thanks
last question so basically I can turn on jumbo frames (to max value) on all my switch in the network.
All my switches are  Cisco some support only 9000 and some 9189 bytes will this not be a problem.
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Assisted Solution

by:Craig Beck
Craig Beck earned 333 total points
ID: 40316338
If you link two switches with different MTU values, set both link interfaces to the lowest value, so if one switch only goes to 9000 set the other switch's uplink to 9000 too.

If you mismatch the MTU you'll get fragmentation problems and dropped traffic.
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