Re: Status of Operational issues with Tiny Fragments in IPv6

[Fred Baker <fred@cisco.com>]

On May 29, 2006, at 6:53 AM, Stig Venaas wrote:
> Also note that as mentioned above, some implementations send  
> fragments out of order (e.g. Linux has been known to do this). The  
> reason is that you don't know the total size of the datagram until  
> you receive the last fragment. Receiving the last fragment first  
> means that you can allocate the right amount of memory immediately.

On that particular point, since packets can be reordered in flight in  
a best effort network, it seems to me that the sender can neither  
prevent packets from arriving last fragment first. a middle box  
cannot accurately detect that the sender did or did not do this, and  
the receiver cannot depend on packets being sent last first. So if it  
happens it happens, but thinking very hard about it sounds like a  
fool's errand. Better to simply hang on to the mblks-or-equivalent  
until the segments have all arrived.