Chapter 13 Spanning Tree Protocol
XGS4700-48F User’s Guide
150
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.
13.1.2 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 26
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 XGS4700 Series
Page 2: ......
Page 8: ...Safety Warnings XGS4700 48F User s Guide 8...
Page 24: ...Table of Contents XGS4700 48F User s Guide 24...
Page 25: ...25 PART I User s Guide...
Page 26: ...26...
Page 32: ...Chapter 1 Getting to Know Your Switch XGS4700 48F User s Guide 32...
Page 54: ...Chapter 3 Hardware Overview XGS4700 48F User s Guide 54...
Page 97: ...97 PART II Technical Reference...
Page 98: ...98...
Page 104: ...Chapter 7 System Status and Port Statistics XGS4700 48F User s Guide 104...
Page 118: ...Chapter 8 Basic Setting XGS4700 48F User s Guide 118...
Page 138: ...Chapter 9 VLAN XGS4700 48F User s Guide 138...
Page 142: ...Chapter 10 Static MAC Forward Setup XGS4700 48F User s Guide 142...
Page 174: ...Chapter 14 Bandwidth Control XGS4700 48F User s Guide 174...
Page 188: ...Chapter 17 Link Aggregation XGS4700 48F User s Guide 188...
Page 198: ...Chapter 18 Port Authentication XGS4700 48F User s Guide 198...
Page 216: ...Chapter 21 Policy Rule XGS4700 48F User s Guide 216...
Page 260: ...Chapter 25 AAA XGS4700 48F User s Guide 260...
Page 284: ...Chapter 26 IP Source Guard XGS4700 48F User s Guide 284...
Page 316: ...Chapter 32 Error Disable XGS4700 48F User s Guide 316...
Page 320: ...Chapter 33 Static Route XGS4700 48F User s Guide 320...
Page 328: ...Chapter 35 RIP XGS4700 48F User s Guide 328...
Page 384: ...Chapter 42 ARP Learning XGS4700 48F User s Guide 384...
Page 420: ...Chapter 45 Access Control XGS4700 48F User s Guide 420...
Page 426: ...Chapter 47 Syslog XGS4700 48F User s Guide 426...
Page 434: ...Chapter 48 Cluster Management XGS4700 48F User s Guide 434...
Page 438: ...Chapter 49 MAC Table XGS4700 48F User s Guide 438...
Page 442: ...Chapter 50 IP Table XGS4700 48F User s Guide 442...
Page 446: ...Chapter 52 Routing Table XGS4700 48F User s Guide 446...
Page 454: ...Chapter 54 Troubleshooting XGS4700 48F User s Guide 454...
Page 464: ...Chapter 55 Product Specifications XGS4700 48F User s Guide 464...
Page 473: ...Appendix B Legal Information XGS4700 48F User s Guide 473...
Page 474: ...Appendix B Legal Information XGS4700 48F User s Guide 474...