[ECOS] Re: [Fwd: FreeBSD network stack question]

[Andrew Lunn]

On Wed, Oct 19, 2005 at 01:21:49PM -0500, Grant Edwards wrote:
> In gmane.os.ecos.general, you wrote:
> 
> > If we collect a packet trace with tcpdump, we see an ARP request and ARP 
> > reply, then we see the 2nd segment of the first message - the first 
> > segment of the first message is never transmitted.
> 
> Now you understand why there's a "U" in "UDP".  ;)

Unreliable Datagram Protocol? Well its actually User Datagram Protocl.

 
> > 1. udp_output calls ip_output
> > [...]
> > 8. ip_output believes that all is well with the first segment and 
> > proceeds to send the second.  By now, the ARP resolution process has 
> > completed, and the second segment is transmitted normally.
> >
> > Is this normal?
> 
> I think so.  UDP packets are allowed to vanish pretty much
> anywhere along the way.

Looking at the code it seems like it will hold onto one packet until
the ARP responce is received. If there are more than one request to
send a packet while the ARP process is still going on, only the last
packet is kept. All others are thrown away.

        Andrew

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