From: Hobbs (deadheadblues@gmail.com)
Date: Mon Aug 04 2008 - 23:01:18 ART
Well I'll try, If I screw up somewhere please let me know guys:-)
Suppose Router A has 3 routes to destination Network B. These routes go
through Router1, Router2, and Router3.
/-----250-----R1-----100-----\
/ \
Router A------300-----R2-----200--------|--------Network B
\ /
\-----100-----R3-----400-----/
These are the reported ("advertised") distances from each neighbor
Router1 reports a metric of 100 to Network B
Router2 reports a metric of 200 to Network B
Router3 reports a metric of 400 to Network B
Router A must also add its distance to each of the routers. So the total
distance are:
Router1: 100+250 = 350
Router2: 200+300 = 500
Router3: 400+100 = 500
Router A will pick the lowest metric as it's successor, this will be the
path through Router1. It will set the feasible distance to 350. Then for a
feasible successor, Router A will compare the reported ("advertised")
distance of the remaining routers to the feasible distance 350.
In order to be a feasible successor R2 or R3 must advertise a distance less
than 350. Router 2 is the only one left that does this (300<350). So even
though R2 and R3 are equal cost, only R2 is feasible successor.
The reason EIGRP does this is because it has no way of knowing if the path
through R3 somehow goes back through itself on to network A. R3's advertised
distance for 400 could very well include Router A's already calculated
feasible distance of 350. EIGRP has no way of knowing this...it would be
nice if it could!
hope that explains it :-)
On Mon, Aug 4, 2008 at 7:32 PM, Mark Stephanus Chandra <
mark.chandra@gmail.com> wrote:
> Hi Hobbs,
>
>
>
> Thanks a lot for the explanation, buta sorry, I still don't get it.
>
>
>
> Sorry if I ask too much, but maybe it is better with a example of simple
> drawing of topology. It can help much.
>
>
>
> Regards
>
>
>
> *Mark Stephanus Chandra
> *IT Consultant
>
>
>
> *From:* Hobbs [mailto:deadheadblues@gmail.com]
> *Sent:* Tuesday, August 05, 2008 7:28 AM
> *To:* Mark Stephanus Chandra
> *Cc:* ccielab@groupstudy.com
> *Subject:* Re: EIGRP Concept
>
>
>
> Feasible successor is not better than the successor :-)
>
> It is better than the successor's reported distance (the distance as
> reported from the neighbor of the successor route).
>
>
>
> On Mon, Aug 4, 2008 at 6:14 PM, Mark Stephanus Chandra <
> mark.chandra@gmail.com> wrote:
>
> dEAR Expert,
>
>
>
> I'm kinda confuse with eigrp concept recently. Just come up in my mind.
>
>
>
> It is about a successor and feasible successor.
>
>
>
> So, In my Understanding of EIGRP concept right now :
>
>
>
> EIGRP will choose the best metric, and become Feasible Distance , right ?
>
>
>
> So If a ROUTE wants to be a feasible successor, It must have better metric
> than feasible distance, right ?
>
>
>
> So, it comes a question, so feasible successor is always better than a
> successor but a successor the one who become the primary route, Why ?
>
>
>
> Because feasible successor have better metric than successor right ?
>
>
>
> Please get me out of my confusion of EIGRP concept right here hehhee.
>
>
>
> Thanks in advance for you all
>
>
>
> Regards
>
>
>
> Mark Stephanus Chandra
> IT Consultant
> EX Computindo
>
>
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