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=41970&t=41957
--------------------------------------------------
FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
