Question : Spanning-tree Cost  to block uplink to core Switches.

Hi Experts,

I am in the process of adding a new 3560 switch and uplink to my Core 1 and Core 2 switches. I need some verification or suggestion for the best practice design.  

I would like to manually send all traffic from Switch C G0/51 to Switch A Core1 and block the path G0/52 to Switch B.

This switch will be for my public network. I created vlan 2 to be assigned to the interface and Vlan 10 is my management VLAN network.

By adding spanning-tree cost 10 int G0/52 will this block all traffic for the interface and send all traffic to int G0/51? In the event that Core switch 1 goes down will the path G0/52 accept traffic and pass all traffic to Core switch 2?


interface Vlan2

 interface Vlan10
 ip address 192.168.1.2 255.255.255.0
 no ip route-cache


interface GigabitEthernet0/51
 switchport access vlan 10
!
interface GigabitEthernet0/52
 switchport access vlan 10
spanning-tree cost 10

Thanks in advance
db

Attachments:

STPBlock-to-core-2.JPG (67 KB) (File Type Details) 

STP blocking uplink to core 2

Answer : Spanning-tree Cost  to block uplink to core Switches.

Here is why it's important to set the root priority on the 2 core switches- it means that if you later replace the 3560 with a switch that happens to have a lower MAC address, the root won't change. This could also happen if you add another switch that connects to the core. The greatest cause of instability on a spanning-tree network is the lack of a predictable root.

Imagine what your spanning-tree design if you were to add another switch and IT became the root? Where would blocking occur? The answer is, it depends. Even modifying the port cost the way you were thinking about would not guarantee that blocking would continue to happen as you want. Set your primary and secondary root and then relax with a cup of coffee.