Open Stack

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