Subject: Re: 'Slow-Start Restart after Idle' draft

From: Joe Touch <[email-masked]>
Date: Thu, 22 Oct 1998 15:51:39 -0700 (PDT)

> Date: Thu, 22 Oct 1998 15:36:00 -0600 (MDT)
> From: Vernon Schryver <[email-masked]>
> To: [email-masked]
> Subject: Re: 'Slow-Start Restart after Idle' draft
> 
...
> > From: Joe Touch <[email-masked]>
> 
> > ...
> > Sending reduced numbers of ACKs can generate line-rate bursts,
> > ...
> 
> Line-rate bursts can be bad, for example when you are talking to a LAN
> that is the first hop in a long and slow link.
> 
> However, line-rate bursts are necessary, desirable, and inevitable on LANs
> if you want to approach the 100% utilization.  That is obvious on token
...

The caveat is that these mechanisms, like slow-start restart,
should be disabled on a LAN. We hadn't put that in the latest
draft, but it is in the revision. It's the same check as slow-start -
if the net prefixes match, ignore the code.

Joe

---

From: Keith Owens <[email-masked]>
Date: Fri, 23 Oct 1998 09:20:13 +1000

On Thu, 22 Oct 1998 15:51:39 -0700 (PDT), 
Joe Touch <[email-masked]> wrote:
>[ACK-burst stuff]

Not having seen the revision yet, what happens if the "LAN" has stubs
behind slower links that are reached using proxy ARP?  Network prefixes
will match, turn off all the congestion mechanisms and overload the
slow links.  Of course we could break our nice flat backbone into lots
of subnets and reprogram all the desktop configurations ...

---

From: Luigi Rizzo <[email-masked]>
Date: Fri, 23 Oct 1998 04:01:02 +0100 (MET)

> if the net prefixes match, ignore the code.

FreeBSD does this as a side effect of the introduction of TTCP, but
this is very bad (and i recently introduced a sysctl variable to
control this behaviour) because in many cases the address block is
further segmented downstream and the sender is unaware of that. Think
of a machine acting as a ppp server by allocating addresses from the
same range as the primary interface and doing proxy arp.

in my opinion, just checking netmasks is very prone to failute and
ignoring slowstart should be explicitly configured if desired.

	cheers
	luigi
-----------------------------+--------------------------------------
Luigi Rizzo                  |  Dip. di Ingegneria dell'Informazione
email: [email-masked]    |  Universita' di Pisa
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