Re: Link State Thought Process

From: Petr Lapukhov (petr@internetworkexpert.com)
Date: Wed Jun 28 2006 - 16:20:03 ART

With pure SPF, there are three steps:

1) First, all link information is _flooded_ through the domain, from
router to router. Thus, a consistent view of topology is achieved.

2) Next, SPF algorithm is being run over topology view (graph) to get
shortest paths

3) With every change, triggered link state update is flooded again,
and SPF calculation is repeated

So there are no reqursive "lookups" after all, just flooding and
computations :)

HTH

2006/6/28, CCIEin2006 <ciscocciein2006@gmail.com>:
>
> No one wants to take a stab? I figured the question might be a little
> junior-level...
>
> On 6/28/06, CCIEin2006 <ciscocciein2006@gmail.com> wrote:
> >
> > Hey guys,
> >
> > I was wondering if anyone could confirm my understanding of link state
> > routing. In the following scenario:
> >
> > RTRA----RTRB----RTRC----RTRD----10.1.1.0
> >
> > For RTRA to enter 10.1.1.0 in its routing table it does the following:
> >
> > 1. Looks in its link state database for 10.1.1.0.
> > 2. Finds 10.1.1.0 is connected to RTRD.
> > 3. Does a recursive lookup to find where RTRD is connected.
> > 4. Finds RTRD is connected to RTRC.
> > 5. Does a recursive lookup to find where RTRC is connected.
> > 6. Finds RTRC is connected to RTRB.
> > 7. Does a recursive lookup to find where RTRB is connected.
> > 8. Finds RTRB is directly connected to Ethernet0.
> > 9. Adds 10.1.1.0 with next hop to RTRB out Ethernet0.
> >
> > If using a distance vector proctocol on the other hand:
> > 1. RTRA learns 10.1.1.0 from RTRB. It doesn't care about anything beyond
> > RTRB.
> > 2. Finds RTRB is directly connected to Ethernet0.
> > 3. Adds 10.1.1.0 with next hop to RTRB out Ethernet0.
> >
> > Is my thinking correct here?
> >
> > Thanks in advance.
>
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-- 
Petr Lapukhov, CCIE #16379
petr@internetworkexpert.com

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