Chapter 11 Spanning Tree Protocol
GS-2724 User’s Guide
102
Path cost is the cost of transmitting a frame onto a LAN through that port. It 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 root port is the port through which this bridge communicates with the root.
It 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.
11.1.2 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.
Table 21
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
Summary of Contents for GS-2724
Page 1: ...www zyxel com GS 2724 Ethernet Switch User s Guide Version 3 70 4 2007 Edition 1 ...
Page 2: ......
Page 7: ...Safety Warnings GS 2724 User s Guide 7 ...
Page 8: ...Safety Warnings GS 2724 User s Guide 8 ...
Page 22: ...Table of Contents GS 2724 User s Guide 22 ...
Page 30: ...List of Tables GS 2724 User s Guide 30 ...
Page 32: ...32 ...
Page 36: ...Chapter 1 Getting to Know Your Switch GS 2724 User s Guide 36 ...
Page 40: ...Chapter 2 Hardware Installation and Connection GS 2724 User s Guide 40 ...
Page 46: ...Chapter 3 Hardware Overview GS 2724 User s Guide 46 ...
Page 48: ...48 ...
Page 58: ...Chapter 4 The Web Configurator GS 2724 User s Guide 58 ...
Page 64: ...Chapter 5 Initial Setup Example GS 2724 User s Guide 64 ...
Page 70: ...Chapter 6 System Status and Port Statistics GS 2724 User s Guide 70 ...
Page 84: ...84 ...
Page 94: ...Chapter 8 VLAN GS 2724 User s Guide 94 Figure 36 Port Based VLAN Setup All connected ...
Page 126: ...Chapter 16 Port Authentication GS 2724 User s Guide 126 ...
Page 130: ...Chapter 17 Port Security GS 2724 User s Guide 130 ...
Page 136: ...Chapter 18 Classifier GS 2724 User s Guide 136 Figure 58 Classifier Example ...
Page 139: ...Chapter 19 Policy Rule GS 2724 User s Guide 139 Figure 59 Policy ...
Page 145: ...Chapter 20 Queuing Method GS 2724 User s Guide 145 ...
Page 146: ...Chapter 20 Queuing Method GS 2724 User s Guide 146 ...
Page 152: ...Chapter 21 VLAN Stacking GS 2724 User s Guide 152 ...
Page 166: ...166 ...
Page 183: ...Chapter 27 DHCP GS 2724 User s Guide 183 Figure 89 DHCP Relay Configuration Example ...
Page 184: ...Chapter 27 DHCP GS 2724 User s Guide 184 ...
Page 186: ...186 ...
Page 210: ...Chapter 31 Syslog GS 2724 User s Guide 210 ...
Page 224: ...Chapter 36 Routing Table GS 2724 User s Guide 224 ...
Page 228: ...228 ...
Page 262: ...Chapter 38 Introducing Commands GS 2724 User s Guide 262 ...
Page 296: ...Chapter 42 IEEE 802 1Q Tagged VLAN Commands GS 2724 User s Guide 296 ...
Page 300: ...Chapter 44 Routing Domain Command Examples GS 2724 User s Guide 300 ...
Page 304: ...304 ...
Page 312: ...Appendix B Changing a Fuse GS 2724 User s Guide 312 ...
Page 332: ...Appendix E Common Services GS 2724 User s Guide 332 ...
Page 336: ...Appendix F Legal Information GS 2724 User s Guide 336 ...
Page 348: ...Index GS 2724 User s Guide 348 ...