Prioritizing STP links from one another

[shawngs16]

Using (5) 2924XL's, A & B @ location 1, C & D @ location 2, and E @ location 3. A, B, C, D all have redundant links to each other. A-->B & A-->C-->D-->B respectively. I want to make sure that if the links A-->C & B-->D are up that they are used all the time. Should the priorities of these ports be changed, or the costs or both? They are all 100FX links btw. Thanks...

[Georg Pauwen]

Hello,

your best bet would probably be to put your redundant links into Etherchannels. This effectively creates one pipe out of two (or more, up to 8) individual links. The Etherchannel runs one instance of STP. There is not really another way to keep redundant links active in a switched networks, because STP will always allow only one path to be active. Since the Etherchannel runs only one instance of STP, this is not a problem.

To configure the Etherchannel, configure you ports as following. In this example, ports Fa0/1 and Fa0/2 on both switches form an Etherchannel. Make sure the configurations on both sides are the same:

SwitchA

interface port-channel 1

switchport trunk encapsulation isl

switchport mode trunk

interface FastEthernet0/1

switchport trunk enapsulation isl

switchport mode trunk

channel-group 1 on

interface FastEthernet0/2

switchport trunk enapsulation isl

switchport mode trunk

channel-group 1 on

SwitchB

interface port-channel 1

switchport trunk encapsulation isl

switchport mode trunk

interface FastEthernet0/1

switchport trunk enapsulation isl

switchport mode trunk

channel-group 1 on

interface FastEthernet0/2

switchport trunk enapsulation isl

switchport mode trunk

channel-group 1 on

HTH,

GP

[shawngs16]

My bad in my original explanation. My description was somewhat inaccurate and misleading. Let me clarify, what I meant was the following. Lets simplify and say I have (4) 2924XL's. A & B in location 1, C & D in location 2. A & B are interconnected locally, as are C & D. Across locations A connects to C and B connects to D. STP and port fasting is enabled. I want to make sure that if the A--> C & B-->D links are available they are always utilized while the local interconnects get blocked. Pardon my first subpar explanation...