Subject: Re: dynamic rwin adjustments

From: Vernon Schryver <[email-masked]>
Date: Thu, 25 Feb 1999 00:30:21 -0700 (MST)

> From: Jamshid Mahdavi <[email-masked]>

>                              ...    The paper covers dynamic tuning of
> the senders socket buffer (and hence sending window).  ...

Yes, I got it backwards.

> ...
> For receiver window, we argue that just setting the window to max (as
> Vernon suggests) is just as effective as dynamically tuning. ...

> Unless you tuned *very* conservatively, tuning would still probably
> allow for situations where loss in the network would fill up all of
> the available memory (mbufs) on the receiver. ...

Be careful not to say that too loudly.  It seems true to me, but I've
heard complaints about the BSD tactic of advertising of more receive window
that real bytes.  Some people feel strongly , or at least once felt, that
the sum of all of the advertised windows should be no more than the
system's available buffering.

Some BSD varients did a good imitation of crashing when they run out of
mbufs.  That's a good reason to build better IP fragment handling than in
original 4.3BSD.  I think there were CERT advisories about denial of
service on some systems involving sending orphan IP fragments.  A system
using `ttcp` to try to send 200 Mbit/sec or more of 8K UDP/IP/FDDI
generates a stream of orphans.  Watching a second system try to listen to
such a stream is one way to discover that lots of surprising system calls
depended on mget().

Vernon Schryver    [email-masked]