Rehashing STP at the moment for CCIE studies and thought I'd make a quick note about the default STP port costs and how they've evolved with link speed increases over time.
Things to note with the table below:
The default costs used by Catalyst switches correspond to the 802.1D-1998 version of the standard if PVST(Per-Vlan Spanning-Tree) or Rapid-PVST(Rapid Per-Vlan Spanning-Tree) are used.
If MSTP (802.1s) is used then Catalyst switches use the default costs that correspond to the 802.1D-2004 version.
Just to make things a little more confusing PVST and Rapid-PVST can be forced into using 802.1D-2004 default port costs via the 'spanning-tree pathcost method long' global configuration command. By default PVST and Rapid-PVST use 'spanning-tree pathcost method short' which causes the switch to us the older revision of the costs(802.1D-1998).
Juniper by default uses the 802.1D-2004 default port costs when either RSTP or MSTP is enabled on its switching equipment.
Port Speed |
Pre-802.1D-1998 Cost |
802.1D-1998 Cost* |
802.1D-2004 Cost** |
10Mbps |
100 |
100 |
2000000 |
100Mbps |
10 |
19 |
200000 |
1000Mbps(1Gbps) |
1 |
4 |
20000 |
10000Mbps(10Gbps) |
1 |
2 |
2000 |
* Cisco Catalyst default for PVST and Rapid-PVST
** Juniper default for RSTP\MSTP & Cisco Catalyst default for MSTP