ZyXEL Communications P-794H User Manual page 133

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 59 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.
7.8.2.2 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 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.
P-794H User's Guide
RECOMMENDE
LINK SPEED
D VALUE
4Mbps 250
10Mbps 100
16Mbps 62
100Mbps 19
1Gbps 4
10Gbps 2
Chapter 7 WAN Setup
RECOMMENDE ALLOWED
D 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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