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Re: [QUANTUM] (Bug ?) L3 routing not correctly fragmenting packets ?


Thanks Rick that makes sense. I've never run into this myself. I just
assumed that a host would by default just set packets at it's MTU size
and the network would handle the fragmentation for you. Good to know.


On Fri, Mar 8, 2013 at 11:56 AM, Rick Jones <rick.jones2@xxxxxx> wrote:
> 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