Re: Windows 7 Ignores TCP MSS?

[Hansang Bae <for_list_hbae () nyc rr com>]

On 3/23/2011 9:11 PM, Robinson, Eric wrote:
> If the NIC has offloading enabled, I guess the stack knows this and 
> sends it bigger frames, knowing it will packetize them smaller? 
> Because I went into the adapter properties and turned off all the 
> offloading features, and now it is being reported as expected in 
> WireShark. So I guess when the NIC's offload capabilities are 
> disabled, the stack detects this and only sends it frames that are 
> appropriate for the MTU?

(wow..sorry for the late reply - it's been hard to keep up on the list!)

Yes, I don't know how it breaks it, but TCP cheats by looking at what 
the MTU is and subtracts the header appropriately to come up with MSS.  
Theoretically, IP is supposed to do that, but I suppose it's one of 
those things that started and no one ever deviated from it.  I do recall 
seeing a post by Rich Seifert on Usenet (when it actually was useful) 
comp.dcom.lans.ethernet explaining how this came to be.  But I don't 
recall the gory details.

hsb

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