Editing Spanning Tree Protocol (section)

=== Path cost ===
{| class="wikitable floatright" style="text-align: right"
|+Path cost for different port speed and STP variation
|-
! Data rate<br />(link bandwidth)
! Original STP cost<br />(802.1D-1998)
! RSTP/MSTP cost<br />(recommended value)<ref name="802.1Q"/>{{rp|503}} 
|-
| {{nowrap|4 Mbit/s}}
| 250
| 5,000,000
|-
| {{nowrap|10 Mbit/s}}
| 100
| 2,000,000
|-
| {{nowrap|16 Mbit/s}}
| 62
| 1,250,000
|-
| {{nowrap|100 Mbit/s}}
| 19
| 200,000
|-
| {{nowrap|1 Gbit/s}}
| 4
| 20,000
|-
| {{nowrap|2 Gbit/s}}
| 3
| 10,000
|-
| {{nowrap|10 Gbit/s}}
| 2
| 2,000
|-
| {{nowrap|100 Gbit/s}}
| N/A
| 200
|-
| {{nowrap|1 Tbit/s}}
| N/A
| 20
|}

The STP path cost default was originally calculated by the formula {{math|{{sfrac|1 Gbit/s|bandwidth}}}}. When faster speeds became available, the default values were adjusted as otherwise speeds above {{nowrap|1 Gbit/s}} would have been indistinguishable by STP. Its successor RSTP uses a similar formula with a larger numerator: {{math|{{sfrac|20 Tbit/s|bandwidth}}}}. These formulas lead to the sample values in the table.<ref name="802.1D-2004">{{cite web |url=http://standards.ieee.org/getieee802/download/802.1D-2004.pdf |archive-url=https://web.archive.org/web/20051210051119/http://standards.ieee.org/getieee802/download/802.1D-2004.pdf |url-status=dead |archive-date=December 10, 2005 |title=802.1D IEEE Standard for Local and Metropolitan Area Networks. Media Access Control (MAC) Bridges |year=2004 |publisher=[[IEEE]] |access-date=19 April 2012}}</ref>{{rp|154}}