On 08/19/2013 06:51 PM, Bill Prince wrote:
Set the interface cost higher = lower priority.
If OSPF has two paths, and one is set to cost of 10, and a second is set
to a cost of 15, it will choose the lower cost path unless it's down.
Note that this is for the entire path to the destination and not just
the one interface hop. for example:
| r1 - r2 -|
0.0.0.0/0 r0- R3
| - r4 - |
SO from r3, you have 2 paths to 0.0.0.0/0. One via "top" interface to
r2, then r1, then r0. Using default costs, that is:
r3 "top" +10
r2 "left" +10
r1 "left" +10
Total cost = 30
Using the other path:
r3 "bottom" +10
r4 "left" +10
Total cost =20
OSPF will use the "bottom" path in that instance. Simply adding 5 to
that interface will look like this:
r3 "bottom" +15
r4 "left" +10
Total cost 25
So the router r3 will STILL use the same path to reach the 0.0.0.0/0
network, since the cost of 25 is still less than 30 going the other way.
If you want to use the other path, the TOTAL cost from the perspective
of the router you want to influence must be greater than the TOTAL cost
of the alternate path to a given destination.
--
Butch Evans
702-537-0979
Network Support and Engineering
http://store.wispgear.net/
http://www.butchevans.com/
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