Chapter 10 Spanning Tree Protocol
GS-2024 User’s Guide
92
Path cost is the cost of transmitting a frame onto a LAN through that port. The recommended
cost is assigned according to the speed of the link to which a port is attached. The slower the
media, the higher the cost.
On each bridge, the bridge communicates with the root through the root port. The root port is
the port on this Switch with the lowest path cost to the root (the root path cost). If there is no
root port, then this Switch has been accepted as the root bridge of the spanning tree network.
For each LAN segment, a designated bridge is selected. This bridge has the lowest cost to the
root among the bridges connected to the LAN.
10.1.2 How STP Works
After a bridge determines the lowest cost-spanning tree with STP, it enables the root port and
the ports that are the designated ports for connected LANs, and disables all other ports that
participate in STP. Network packets are therefore only forwarded between enabled ports,
eliminating any possible network loops.
STP-aware switches exchange Bridge Protocol Data Units (BPDUs) periodically. When the
bridged LAN topology changes, a new spanning tree is constructed.
Once a stable network topology has been established, all bridges listen for Hello BPDUs
(Bridge Protocol Data Units) transmitted from the root bridge. If a bridge does not get a Hello
BPDU after a predefined interval (Max Age), the bridge assumes that the link to the root
bridge is down. This bridge then initiates negotiations with other bridges to reconfigure the
network to re-establish a valid network topology.
10.1.3 STP Port States
STP assigns five port states to eliminate packet looping. A bridge port is not allowed to go
directly from blocking state to forwarding state so as to eliminate transient loops.
Table 20
STP Path Costs
LINK
SPEED
RECOMMENDED
VALUE
RECOMMENDED
RANGE
ALLOWED
RANGE
Path
Cost
4Mbps
250
100 to 1000
1 to 65535
Path
Cost
10Mbps
100
50 to 600
1 to 65535
Path
Cost
16Mbps
62
40 to 400
1 to 65535
Path
Cost
100Mbps
19
10 to 60
1 to 65535
Path
Cost
1Gbps
4
3 to 10
1 to 65535
Path
Cost
10Gbps
2
1 to 5
1 to 65535
Table 21
STP Port States
PORT STATE DESCRIPTION
Disabled
STP is disabled (default).
Blocking
Only configuration and management BPDUs are received and processed.
Summary of Contents for Dimension GS-2024
Page 2: ......
Page 7: ...Safety Warnings GS 2024 User s Guide 7 This product is recyclable Dispose of it properly ...
Page 8: ...Safety Warnings GS 2024 User s Guide 8 ...
Page 26: ...List of Tables GS 2024 User s Guide 26 ...
Page 28: ...28 ...
Page 36: ...Chapter 2 Hardware Installation and Connection GS 2024 User s Guide 36 ...
Page 44: ...44 ...
Page 62: ...Chapter 6 System Status and Port Statistics GS 2024 User s Guide 62 ...
Page 70: ...Chapter 7 Basic Setting GS 2024 User s Guide 70 Figure 27 Basic Setting IP Setup ...
Page 74: ...Chapter 7 Basic Setting GS 2024 User s Guide 74 ...
Page 76: ...76 ...
Page 88: ...Chapter 8 VLAN GS 2024 User s Guide 88 ...
Page 110: ...Chapter 13 Mirroring GS 2024 User s Guide 110 ...
Page 120: ...Chapter 15 Port Authentication GS 2024 User s Guide 120 ...
Page 138: ...Chapter 18 Multicast GS 2024 User s Guide 138 ...
Page 152: ...Chapter 19 Authentication Accounting GS 2024 User s Guide 152 ...
Page 157: ...157 PART IV IP Application Static Route 159 Differentiated Services 163 DHCP 167 ...
Page 158: ...158 ...
Page 162: ...Chapter 21 Static Route GS 2024 User s Guide 162 ...
Page 166: ...Chapter 22 Differentiated Services GS 2024 User s Guide 166 ...
Page 174: ...174 ...
Page 198: ...Chapter 25 Access Control GS 2024 User s Guide 198 ...
Page 200: ...Chapter 26 Diagnostic GS 2024 User s Guide 200 ...
Page 204: ...Chapter 27 Syslog GS 2024 User s Guide 204 ...
Page 218: ...218 ...
Page 222: ...Chapter 32 Troubleshooting GS 2024 User s Guide 222 ...
Page 230: ...Chapter 33 Product Specifications GS 2024 User s Guide 230 ...
Page 232: ...232 ...
Page 240: ...Appendix A Pop up Windows JavaScripts and Java Permissions GS 2024 User s Guide 240 ...
Page 252: ...Appendix C Legal Information GS 2024 User s Guide 252 ...
Page 258: ...Appendix D Customer Support GS 2024 User s Guide 258 ...
Page 266: ...Index GS 2024 User s Guide 266 ...