From: Fred Ingham (fningham@xxxxxxxxxxxxxxxx)
Date: Tue Mar 28 2000 - 02:27:04 GMT-3
First, on r1 use the bridge 1 priority 100 command to force r1 as root.
Next, the key is to assign a path cost to r2 S0 of 647 + 99 = 746. The
number doesn't have to be 99 just so the path costs line up as:
r2 cost to r1 is less thru s0 - in this case 746 vice 747 thru e0.
r3 cost to r1 is less thru s0 - in this case 647 vice 846 thru
e0.
r3 and r2 S0's will be root ports and one of r2 e0 or r3 e0
will be blocking. Since the root path cost thru r2 e0 is
746 and the root path cost thru r3 e0 is 647, r3 e0 will become
the designated port and r2 e0 will block.
Note: your cost of 647 is due to the default bandwidth on the
serial of 1.544Mbps (1000/1.544 = 647). Changing the bandwidth
can also change the cost.
clou@ebnetworks.com wrote:
>
> Fred,
>
> Good explanation.
>
> I did try scenario 6 in the lab earlier. It seems very straight
> forward in the beginning; however, it took me almost 45 minutes
> to get the result as per the requirement - place R2 E0 in blocking
> state.
>
> In essence, you'll think just put a very high port path-cost on
> R2 E0 and it's done. Not so fast, my friend...I was wrong. Once
> I put "bridge-group 1 path-cost 65000" on R2 E0, it is still in
> forwarding state and R3 E0 is in bloking state!
>
> To be more specific, in my lab, the port path cost are as follow,
> * R2 S0 - 647, R2 E0 - 100
> * R3 S0 - 647, R2 E0 - 100
>
> With the path-cost range 0 - 65535, how would you solve this
> problem - place R2 E0 in blocking state?
>
> Bruce gave a good example (page 590) but didn't explain how he
> came up with that magic number - 499!
>
> Any suggestion? Thanks. (sorry I've wiped out the config and
> can't post it here)
>
> Chi
>
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