How Stp Works; Stp Port States; Table 25 Stp Port States - ZyXEL Communications VDSL SWITCH VES-1616F-3X User Manual

Chapter 10 Spanning Tree Protocol
Table 24 STP Path Costs
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 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 25 STP Port States

PORT STATE
Disabled
Blocking
Listening
Learning
Forwarding
102
LINK RECOMMENDED
SPEED VALUE
100Mbps 19
1Gbps 4
10Gbps 2
DESCRIPTION
STP is disabled (default).
Only configuration and management BPDUs are received and processed.
All BPDUs are received and processed.
All BPDUs are received and processed. Information frames are submitted to the
learning process but not forwarded.
All BPDUs are received and processed. All information frames are received and
forwarded.
RECOMMENDED ALLOWED
RANGE RANGE
10 to 60 1 to 65535
3 to 10 1 to 65535
1 to 5 1 to 65535
VES-1616F-3x Series User's Guide