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On 03/08/2013 11:49 AM, Aaron Rosen wrote:
Hi Rick, You are right. I just ran curl to test for myself and it does set the DF bit. Why is this? Any ideas why it specifies that the packet cannot be fragmented?
Because most, if not virtually all TCP stacks going back to the mid 1990s (RFC 1191 is from 1990 and I figured a couple years to propagate) enable Path MTU discovery by default for TCP. At least those with which I have come into contact.
I doubt that curl itself asked for it. I suspect you will find the DF bit set in the IP datagrams carrying the TCP segments of any application on your system using TCP - even netperf :) PathMTU discovery, for TCP at least, and perhaps other "reliable" transports, is considered a Best Practice (tm) and so enabled by default. Where it may not be enabled by default is for UDP.
rick
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