Excellent description John. Reinforced my understanding of FD and AD
Tim
On 19 Apr 2002 12:07:22 -0400, [EMAIL PROTECTED] ("John
Neiberger") wrote:
>The key words here are Feasible Distance and Advertised Distance, or in
>this case, reported distance. The FD is the metric for the current
>path. If we have two neighbors who are reporting that they can reach
>that network, both will be advertising what *their* FD is, which from
>our perspective is the Advertised Distance.
>
>
>[RA]-------(10)--------[RB]-----(50)-----Network Z
> \ /
> \ /
> \------(20)--------[RC]-----(50)------/
>
>
>Imagine that somewhere beyond Routers B and C is a Network, Z. They
>each have a metric of 50 to that network, which is their FD. Router A
>will see two available routes to Z but the one through B has a lower
>metric and it will be installed into the routing table.
>
>However, because RC's Advertised Distance to Z (50) is less than Router
>A's current FD (60), it will be installed as a feasible successor. If
>the metric from Router C to Network Z was 60 or over, it would not be a
>feasible successor. In that case, if the link from A to B were to go
>away, A would not immediately begin using RC as the next hop to Z.
>Instead it would send queries to all of its EIGRP neighbors and it would
>start forwarding to C after C answers that it can reach Z.
>
>I hope that makes sense. I have a cold and am fairly medicated right
>now. ;-)
>
>John
>
>
>>>> "Sean Wolfe" 4/19/02 9:34:03 AM >>>
>EIGRP question:
>
>According to Cisco's website: "Feasible distance is the best metric
>along a
>path to a destination network, including the metric to the neighbor
>advertising that path. A feasible successor is a path whose reported
>distance is less than the feasible distance."
>
>But wouldn't a route with a distance less than the feasible distance be
>in
>the routing table already, since it had a better metric?
>
>It makes more sense to me that the feasible successor is a route with
>a
>slightly larger metric than the current route. That way if the current
>route
>dies, the next-best path is promoted.
>
>But that's not what I'm reading at
>http://www.cisco.com/warp/public/103/eigrp1.html#6
>
>So . . . whaddya say?
>
>Thanks, -Sean.
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=41989&t=41957
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