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Re: multi-homing fixes

  • From: Joel Baker
  • Date: Sat Sep 01 17:50:14 2001

On Sat, Sep 01, 2001 at 10:34:31PM +0200, Iljitsch van Beijnum wrote:
> 
> On Sat, 1 Sep 2001, Joel Baker wrote:
> 
> [SCTP]
> 
> > Me, I prefer to build a new car that's fully up to new design specs, rather
> > than try to retrofit rocket boosters onto the old Studebaker. This isn't to
> > claim, in any way, that "TCP is dead", mind you; but SCTP answers a fairly
> > fundamental set of problems, with a different set of design goals than TCP
> > and UDP were written for. Trying to mangle TCP to accomodate those goals
> > seems likely to produce more confusion than viable code.
> 
> SCTP is a protocol designed to carry telephony signalling.

And bears about as much resembleance to this origion as TCP does to the
military's origional purposes for having a network.

> Being able to use multiple IP addresses per session is not something that
> is inherently more appropriate for telephony signalling than for network
> applications that use stream-based communication. It is a nice option to
> have for any transport protocol.

Agreed.

> So unless there is _another_ reason why SCTP is appropriate for a certain
> application, it seems pretty clear to me that using TCP, which was
> designed to work with the protocols we use on the Net, and is the
> transport protocol applications expect, is much more appropriate.
> Extending TCP to use multiple IP addresses is not a problem. TCP has been
> extended in many ways in the past. And an experimental implementation has
> been available for four years.

RFC/Draft/URL/code? I have yet to see anything which allows the sort of
clean and direct setup which SCTP does, but I certainly haven't made an
exhaustive search of the field. Certainly, if it addresses all of the same
issues while being more compatible and requiring fewer changes, I would be
all for it.

> > As for the 'SCTP isn't backwards compatible with older TCP'
> > claim... uhm, TCP isn't backwards compatible with UDP, either. Your point?
> 
> But nobody is proposing to have applications built for UDP run over TCP.

I might argue that, but it would degenerate into nitpicking. However, I
will grant that a conversion to SCTP would affect a significantly larger
portion of the network than any example I could present as a counter.

> I'm not against implementing new protocols that aren't backward
> compatible, but I'm merely saying that in this case the benefits are too
> small. And comparing this to IPv6: how many people are using IPv6 today?
> Sometimes it is necessary to forego backward compatibility, but that
> decission should never be taken lightly.

I believe that was part of my point, in starting. Both SCTP and IPv6
provide benefits. However, neither appears to be making much headway in the
direction of being adopted by the majority of the Internet. I really wonder
whether any such major change will, since it is no longer practical for a
central agency to say "support for <X> protocol will cease as of <date>".
-- 
***************************************************************************
Joel Baker                           System Administrator - lightbearer.com
lucifer@lightbearer.com              http://www.lightbearer.com/~lucifer