How Stp Works; Stp Port States; Table 23 Stp Port States - ZyXEL Communications ZyXEL Dimension ES-2048 User Manual

ES-2048 User's Guide
Table 22 STP Path Costs
LINK SPEED RECOMMENDED VALUE
Path Cost 16Mbps
Path Cost 100Mbps
Path Cost 1Gbps
Path Cost 10Gbps
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.

11.1.3 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 23 STP Port States

PORT STATE DESCRIPTION
Disabled
Blocking
Listening
106
62
19
4
2
STP is disabled (default).
Only configuration and management BPDUs are received and processed.
All BPDUs are received and processed.
RECOMMENDED
RANGE
40 to 400
10 to 60
3 to 10
1 to 5
Chapter 11 Spanning Tree Protocol
ALLOWED RANGE
1 to 65535
1 to 65535
1 to 65535
1 to 65535