Changing the STP Settings:

There are 2 tools available to change the STP Settings:

1. Configure BID

2. Configure STP Port costs

Configure BID:

• BID consists of Bridge Priority + MAC Address. We cannot configure MAC Address as it is a burned in MAC Address. Hence we can change the priority of a Switch.

• Default Priority is 32768

• Admin can reduce the Priority to make that Switch a Root Bridge.

Configure STP Port costs:

• Default Port Costs:

Ethernet Speed	IEEE Cost: (1998 & Before) Short Path Cost Method Port Cost	IEEE Cost: (2004 & After) Long Path Cost Method Port Cost
10 Mbps	100	2,000,000 (2 Million)
100 Mbps	19	200,000 (2 Hundred Thousand)
1 Gbps	4	20,000
10 Gbps	2	2000
100 Gbps	N/A	200
1 Tbps	N/A	20

• Reduce the port cost to favor the link & increase the port cost to avoid the link.

• You can change the Short/Long port cost by using (#spanning-tree pathcost method (short/long)) command.

Reference:

• CCNA 200-301 OCG, Volume 1, Pg. 223-224- Wendell Odom.