How Stp Works; Stp Port States; Table 11 Stp Path Costs; Table 12 Stp Port States - ZyXEL Communications G-3000 User Manual

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 - see the following table.

Table 11 STP Path Costs

Path Cost
Path Cost
Path Cost
Path Cost
Path Cost
Path 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 bridge 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.

6.4.3 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 bridges 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.

6.4.4 STP Port States

STP assigns five port states (see next table) 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 12 STP Port States

PORT STATES
Disabled
Blocking
Listening
G-3000 Series User's Guide
RECOMMENDED
LINK SPEED
VALUE
4Mbps 250
10Mbps 100
16Mbps 62
100Mbps 19
1Gbps 4
10Gbps 2
DESCRIPTIONS
STP is disabled (default).
Only configuration and management BPDUs are received and processed.
All BPDUs are received and processed.
Chapter 6 Wireless Configuration
RECOMMENDED ALLOWED
RANGE RANGE
100 to 1000 1 to 65535
50 to 600 1 to 65535
40 to 400 1 to 65535
10 to 60 1 to 65535
3 to 10 1 to 65535
1 to 5 1 to 65535
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