From: Todd Carswell (acarswell@xxxxxxxxx)
Date: Thu Mar 28 2002 - 19:00:54 GMT-3
Sean,
Sorry, man. I ain't tryin' to step on any toes here.
Here's my point: Poison reverse is referenced in the literature when
they're talking about split-horizon. Routers will use one of the the
following 2 split-horizon techniques:
1. Plain ole split-horizon
2. Split-horizon with poison-reverse
The key word here is "reverse".
The quote you referenced here speaks to this: "Poisoned reverse sends an
update back to the originator..." (Key words: "back" and "originator") In
this situation the "originator" is closer to the advertised network than the
receiver. The router who received the advertised route, if it is using
split-horizon with poison reverse, will advertise the route back out the
same interface it was received on. It will give it an unreachable metric so
that routing loops are avoided. If it's using plain ole split-horizon, it
will not advertise the route back to the originator at all.
With that said, if a network goes down, the "originator" will, in turn,
advertise the network to the "receiver" with an unreachable metric. Do you
see the difference here? The "originator" may or may not be using
split-horizon with poison reverse. It's just simply letting the downstream
neighbors know that the network is down.
That's all I was trying to point out. Poison reverse is always mentioned in
the context of Split-Horizon.
Thanks
Todd Carswell
----- Original Message -----
From: "Sean C" <Upp_and_Upp@hotmail.com>
To: "Todd Carswell" <acarswell@nc.rr.com>; "Ma Gang" <matthen@zisco.com.cn>;
<ccielab@groupstudy.com>
Sent: Thursday, March 28, 2002 2:50 PM
Subject: Re: Off topic, What does "Poison" mean here?
> Todd,
>
> Never wrote that the network couldn't be reached. The network is
advertised
> with a 'spoiled' response - ie hop of 16, etc.
>
> Per one brilliant author of "Designing Routing and Switching
Architectures",
> p285 - "Poisoned reverse sends an update back to the originator, but with
an
> infinite metric to indicate the sending router believes the route to be
> down." Infinite metric, spoiled response, poisoned network.
>
> Sean
> ----- Original Message -----
> From: "Todd Carswell" <acarswell@nc.rr.com>
> To: "Todd Carswell" <acarswell@nc.rr.com>; "Sean C."
> <Upp_and_Upp@hotmail.com>; "Ma Gang" <matthen@zisco.com.cn>;
> <ccielab@groupstudy.com>
> Sent: Thursday, March 28, 2002 1:12 PM
> Subject: Re: Off topic, What does "Poison" mean here?
>
>
> > Sean,
> >
> > Actually, the router who is utilizing "poison reverse" can, in fact,
reach
> > the destination in question. If it could not reach it, then it would
not
> be
> > in any routing updates.
> >
> > In essence, the "poison-reverse" router is telling it's neighbor, "Hey,
I
> > can reach this network, but you told me about it so don't try to reach
it
> > through me!"
> >
> > Todd
> >
> >
> > ----- Original Message -----
> > From: "Todd Carswell" <acarswell@nc.rr.com>
> > To: "Sean C." <Upp_and_Upp@hotmail.com>; "Ma Gang"
<matthen@zisco.com.cn>;
> > <ccielab@groupstudy.com>
> > Sent: Thursday, March 28, 2002 12:46 PM
> > Subject: Re: Off topic, What does "Poison" mean here?
> >
> >
> > > I view "poison reverse" as another way of saying that "bad news is
> better
> > > than no news at all".
> > >
> > > Todd Carswell
> > >
> > >
> > >
> > > ----- Original Message -----
> > > From: "Sean C." <Upp_and_Upp@hotmail.com>
> > > To: "Ma Gang" <matthen@zisco.com.cn>; <ccielab@groupstudy.com>
> > > Sent: Thursday, March 28, 2002 1:16 AM
> > > Subject: Re: Off topic, What does "Poison" mean here?
> > >
> > >
> > > > Hi Matthew,
> > > >
> > > > Per Perlman "Interconnections, 2nd Ed." p 306 - "Poison reverse
means
> > > > reporting a value of infinity to explicitly report that you can't
> reach
> > D
> > > > rather than simply not mentioning D." So, instead of not
> acknowledging
> > > > something, the issue in question is acknowledged, but with an answer
> > that
> > > is
> > > > not valid, thus 'spoiling' the output.
> > > >
> > > > Is this what you are asking or are you asking why was 'poison'
chosen
> > > > instead of words such as 'corrupt' or 'defile'?
> > > >
> > > > Sean
> > > > ----- Original Message -----
> > > > From: "Ma Gang" <matthen@zisco.com.cn>
> > > > To: <ccielab@groupstudy.com>
> > > > Sent: Wednesday, March 27, 2002 7:01 PM
> > > > Subject: Off topic, What does "Poison" mean here?
> > > >
> > > >
> > > > Dear All,
> > > >
> > > > We may be familiar with "Route Poisoning" or "Poison Reverse". But
> what
> > > does
> > > > "poison" mean here? As I imagine, there may be 2 answers
> > > >
> > > > 1. The name of a French mathematician. He invented the algorithm,
> which
> > is
> > > > used in Distance Vector routing protocol now.
> > > >
> > > > 2. Another expression way of "block".
> > > >
> > > > Which one is correct? Or maybe some other answers?
> > > >
> > > >
> > > >
> > > > Matthew Ma
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