[e2e] TCP Option Negotiation

Bob Braden braden at ISI.EDU
Thu May 17 09:15:37 PDT 2001

  *> From hari at chive.lcs.mit.edu  Thu May 17 08:57:44 2001
  *> To: Bob Braden <braden at ISI.EDU>
  *> cc: end2end-interest at postel.org
  *> Subject: Re: [e2e] TCP Option Negotiation 
  *> Mime-Version: 1.0
  *> Date: Thu, 17 May 2001 11:57:39 -0400
  *> From: Hari Balakrishnan <hari at chive.lcs.mit.edu>
  *> > Alex,
  *> > 
  *> > This seems to be another manifestation of the standard  problem of old
  *> > duplicate packet.   Your scenario is a violation of TCP's "quiet time"
  *> > requirement upon host crash and restart (it's the same host if it has
  *> > the same IP address).  Quiet time is a vital part of TCP's machinery to
  *> > protect against old duplicates.
  *> Bob,
  *> Not quite.
  *> Unfortunately the statement: "it's the same host if it has the same IP address" 
  *> is increasingly untrue because of dynamic IP address assignment (e.g., via 
  *> DHCP).  This may well be a theoretical problem, but I've observed (in my home, 
  *> from my FreeBSD DHCP server), turning off a laptop and turning another one on, 
  *> and having the latter receive the former's IP!
  *> Hari


No, my statement is exactly true as far as TCP is concerned; it is the
IP address that identifies the host.  You are saying that immediate
reuse of IP addresses is a fact of life.  OK, we have built an Internet
that consistently violates TCP's reliability mechanism.  That should be
a cause of concern to somebody...

Bob Braden

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