From owner-freebsd-current  Wed Apr 23 14:11:29 1997
Return-Path: <owner-current>
Received: (from root@localhost)
          by hub.freebsd.org (8.8.5/8.8.5) id OAA23601
          for current-outgoing; Wed, 23 Apr 1997 14:11:29 -0700 (PDT)
Received: from root.com (implode.root.com [198.145.90.17])
          by hub.freebsd.org (8.8.5/8.8.5) with ESMTP id OAA23592
          for <current@freebsd.org>; Wed, 23 Apr 1997 14:11:22 -0700 (PDT)
Received: from localhost (localhost [127.0.0.1]) by root.com (8.8.5/8.6.5) with SMTP id OAA06084; Wed, 23 Apr 1997 14:12:56 -0700 (PDT)
Message-Id: <199704232112.OAA06084@root.com>
X-Authentication-Warning: implode.root.com: localhost [127.0.0.1] didn't use HELO protocol
To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu>
cc: Sujal Patel <smpatel@prognet.com>, current@freebsd.org
Subject: Re: Possible networking bug in 2.2.1-Release 
In-reply-to: Your message of "Wed, 23 Apr 1997 10:16:10 EDT."
             <199704231416.KAA17910@khavrinen.lcs.mit.edu> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Wed, 23 Apr 1997 14:12:55 -0700
Sender: owner-current@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk

><<On Wed, 23 Apr 1997 00:24:26 -0700 (PDT), Sujal Patel <smpatel@prognet.com> said:
>
>>         /*
>>          * Verify that we have any chance at all of being able to queue
>>          *      the packet or packet fragments
>>          */
>>         if ((ifp->if_snd.ifq_len + ip->ip_len / ifp->if_mtu + 1) >= 
>>		ifp->if_snd.ifq_maxlen) {
>>                         error = ENOBUFS;
>>                         goto bad;
>>         }
>
>This code is bogus, but it is unlikely to be the problem that you are
>seeing.
>
>There are three things wrong with this code:
>
>1) It has a slow divide.
>2) Fragments are a case to worry about on the slow path.
>3) It knows far too much about the drop-tail queueing strategy.
>
>(3) really bites, and when I implemented RED last year I tossed it
>completely.  Unfortunately, my RED work has not made it into the main
>line of FreeBSD yet.  I hope it will, some day, but it may take a
>while before I have an environment where I can test it again.

   Well, I wrote those lines of code. I'd be happy to see them go as long as
the problem that they address is solved some other way. The problem of course
is that one doesn't want fragments to be transmitted unless all of them can
be sent. Otherwise an aggressive application will send out pieces of packets,
clogging up the network with useless junk and not make any forward progress.

-DG

David Greenman
Core-team/Principal Architect, The FreeBSD Project