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Jumbo Frames and DF bit

Answered Question
Dec 16th, 2013
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Enabling Jumbo Frames on UCS doesn't seem to set the DF bit ? correct ?


Can this be set by UCSM and/or CLI ?

Correct Answer by richbarb about 3 years 8 months ago

Once I did the test about the jumbo frames network performance and can't see any significant difference.


In that time I used a oracle RAC installed in the UCS and a NetApp Filer with DNFS configuration.

In the UCS you must configure MTU in two different places (QoS configuration and vNIC configuration).


In your test with df-bit flag enabled use the packet size maximum of 8972.

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Walter Dey Mon, 12/16/2013 - 04:25
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Thanks for this pointer


UCS customer uses Jumbo frames for NFS, connecting to a Netapp Filer which is in a different IP subnet.


He compared performance with standard Ethernet frame size and Jumbo frames, and didn't see any difference.


I therefore proposed to do a test from ESXi


vmkping -I vmk2 -d -s 9000 192.168.......

vmkping -I vmk2 -d -s 1500 192.168.......


which fails, however


vmkping -I vmk2 -s 9000 192.168.......

vmkping -I vmk2 -s 1500 192.168.......


works ok


Therefore, somewhere in the network between UCS and Netapp, there must be a problem.


It seems, that typical OS (e.g. ESXi) don't set the DF flag.

Correct Answer
richbarb Mon, 12/16/2013 - 04:36
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Once I did the test about the jumbo frames network performance and can't see any significant difference.


In that time I used a oracle RAC installed in the UCS and a NetApp Filer with DNFS configuration.

In the UCS you must configure MTU in two different places (QoS configuration and vNIC configuration).


In your test with df-bit flag enabled use the packet size maximum of 8972.

Walter Dey Mon, 12/16/2013 - 05:03
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8970 was the solution ! Thanks Richard !

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