I think it's a question of total throughput. If the RP has to hit every packet, then
you will have a queue full of packets waiting their turn to get out. By using the SP,
those packets that must be processed by the RP will get through that queue much sooner.
And that paired with the SP's higher speed makes the entire system more efficient.
This
is my take on the process. A bit simplistic, but I's just a simple guy.
Rob
"Taylor, Don" wrote:
> I can see where you're coming from, and maybe I would have worded it
> differently if I'd written the book (i.e. "Why leave it up to the route
> processor when it can be switched faster?"); but do keep in mind that the
> CPU in a router isn't exactly cutting edge technology. If you read the
> specs, most of them are similar to those in computers that we all lusted for
> five years ago. That being the case, the argument is a good one: take as
> much burden off the processor as possible by reducing the number of lookups.
>
> - Don
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> Sent: Monday, January 22, 2001 8:42 PM
> To: [EMAIL PROTECTED]
> Cc: [EMAIL PROTECTED]
> Subject: Re: But isn't that the routers job???
>
> Hi Tony,
> I understand all of this fully but where I'm confused is, how much of a
>
> burden could this be if that's all it has to do. I want to know what the
> "more important" things are...Maybe I overestimate the power of a route
> processor but I would think that its especially created with the power to
> handle tons of routing considering that that's what its designed for...am I
> wrong?
>
> Mark Z.....
>
> In a message dated 1/22/01 11:27:41 PM Eastern Standard Time,
> [EMAIL PROTECTED] writes:
>
> > Hi,
> >
> > My understanding is that routers perform basically two functions one is to
>
> > route that is to find the best path a given message should take and the
> > other is to switch that is once the route is known to send the data to the
>
> > appropriate interface. I think what they are saying in the book. If you
> > know the path a message should take that is the route then why go through
> > the procedure of identifying it again why not just switch it.
> >
> > I know what I'm trying to say. What they say in the book is right "why
> > burden the CPU".
> >
> > Teunis,
> > Hobart, Tasmania
> > Australia
> >
> >
> > On Monday, January 22, 2001 at 11:05:02 PM, [EMAIL PROTECTED] wrote:
> >
> > > Hey Group,
> > > Me again. I'm reading for my CIT and am at the section where it
> goes
> > > into detail of the various switching methods in the router (i.e.,
> > silicon,
> > > CEF, autonomous, etc.) I understand how all this works and understand
> how
> > the
> > > SP takes a lot of the stress away from the RP and this is good because
> > your
> > > avoiding bogging the RP/CPU down. I have a problem with these statements
>
> > > though and want some clarification...
> > >
> > > Taken form the book (Lammle's CIT p. 173):
> > >
> > > "This is just another reason why switching is such a good practice.
>
> > Why
> > > burden the RP with every packet if it's not necessary? By using
> switching
> > > methods, the RP is free to use valuable CPU time on more important
> things
> > > than doing route lookups for every packet that comes in the router."
> > >
> > > Correct me if I'm wrong but isn't that what a routers supposed to do???
> > What
> > > else does the RP have to do that is more important than ROUTING? I may
> be
> > > overanalyzing this but it just seems that he's saying that the RP has
> > better
> > > things to do like make coffee, rather than route.
> > >
> > > Basically, could somebody give me a list of some other things the RP/CPU
>
> > has
> > > to do other than route lookups...(I know there are access-lists and
> other
> > CPU
> > > things here, I just would like a solid list to remember). Thanks team,
> > >
> > > Mark Zabludovsky ~ CCNA, CCDA, 3/4-NP
> > > <A HREF="mailto: [EMAIL PROTECTED]">[EMAIL PROTECTED]</A>
> > >
> > > "Even if I knew I had only 1 more week to live, I would still
> > schedule
> > > my CCIE lab. I would just have to work a little harder I guess. After
> > all,
> > > without any goals in life, I'm dead already."
> > > ~Mark
> Zabludovsky~
> >
>
> Mark Zabludovsky ~ CCNA, CCDA, 3/4-NP
> <A HREF="mailto: [EMAIL PROTECTED]">[EMAIL PROTECTED]</A>
>
> "Even if I knew I had only 1 more week to live, I would still schedule
> my CCIE lab. I would just have to work a little harder I guess. After all,
> without any goals in life, I'm dead already."
> ~Mark Zabludovsky~
>
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