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Community Member

jumbo frames

We are thinking of allowing jumbo frames in our server environment, especially for isci traffic, but i want to double check my interpretation before implementing this (devices to use are 65XX-Sup720 in VSS and 3750-E clusters.

Are the following assumptions ok ?

1) L2 devices don't fragment jumbo frames but just accept or reject them based on the defined mtu on the switch ?

2) L3 devices fragment jumbo frames if needed.

So in a network that only connects isci devices (clients and nas) in a L2 vlan, all switch ports should be jumbo frames enabled to make this work and there is no negotiation between end-stations about the maximum packet size.

Greetings,

Wim Holemans

1 REPLY
Cisco Employee

Re: jumbo frames

Wim,

Your assumptions are correct. Regarding your statement:

So in a network that only connects isci devices (clients and nas) in a L2 vlan, all switch ports should be jumbo frames enabled to make this work and there is no negotiation between end-stations about the maximum packet size.

While there is no real negotiation in this case, you do need to consider the role played by TCP MSS. If you do not bump up the MTU of a server interface (leave it at 1500 for example) then it will report it's MSS as 1460 and any client establishing a TCP session with this server on the same segment will need to respect this value.

Atif

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