Solved: Basic query on STP behaviour: Fiber path Vs Gig Ethernet

mvsheik123 · ‎01-07-2010

Hi all,

Switch 1 STP root and Switch 2 is access switch.

Switch 2 gig 0//25 : Fiber port (1000Base SX SFP) <-- Trunk--> Switch 1 gig 3/10 Fiber port (1000Base SX)

2nd connection..

Switch2 gigEth 0/24 : <--- Trunk---> Sw1 gigEth 4/10

Will STP makes the Fiber port (gig 0/25) as forwaring port on SW2 or gigE (0/24)?

TIA

MS

Jon Marshall · ‎01-07-2010

mvsheik123 wrote:

Thank you Jon.Thats what I guessed. Is there anyway I can make the fiber port to be the forwarding and gig eth blocked?

TIA

MS

Yes, you can alter the port cost so that the cost of the path to root is not the same -

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_44_se/command/reference/cli3.html#wp1945601

Jon

View solution in original post

Jon Marshall · ‎01-07-2010

mvsheik123 wrote:
Hi all,
Switch 1 STP root and Switch 2 is access switch.
Switch 2  gig 0//25 : Fiber port (1000Base SX SFP) <-- Trunk--> Switch 1 gig 3/10 Fiber port (1000Base SX)
2nd connection..
Switch2 gigEth 0/24 :  <--- Trunk---> Sw1 gigEth 4/10 
Will STP makes the Fiber port (gig 0/25) as forwaring port on SW2 or gigE (0/24)?
TIA
MS

MS

gig0/24 should become the forwarding port. If there is a tie in the path cost and there will be in your example the next tie-breaker is to use the lowest port number.

Jon

mvsheik123 · ‎01-07-2010

Thank you Jon.Thats what I guessed. Is there anyway I can make the fiber port to be the forwarding and gig eth blocked?

TIA

MS

Jon Marshall · ‎01-07-2010

mvsheik123 wrote:

Thank you Jon.Thats what I guessed. Is there anyway I can make the fiber port to be the forwarding and gig eth blocked?

TIA

MS

Yes, you can alter the port cost so that the cost of the path to root is not the same -

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_44_se/command/reference/cli3.html#wp1945601

Jon

mvsheik123 · ‎01-07-2010

Thank you. So if I leave the fiber port cost intact (4) and make the gigeth 8, the fiberpath should takeover. Thanks Jon.

Jon Marshall · ‎01-07-2010

mvsheik123 wrote:

Thank you. So if I leave the fiber port cost intact (4) and make the gigeth 8, the fiberpath should takeover. Thanks Jon.

Yes it should.

Jon