Asus GigaX2024SX - Manual (Page 117)

Spanning Tree Algorithm Configuration
The Spanning Tree Algorithm (STA) can be used to detect and disable network
e over when a primary link goes down.
The spanning tree algorithms supported by this switch include these versions:
• STP – Spanning Tree Protocol (IEEE 802.1D)
• RSTP – Rapid Spanning Tree Protocol (IEEE 802.1w)
STA uses a distributed algorithm to select a bridging device (STA-compliant
switch, bridge or router) that serves as the root of the spanning tree network. It
selects a root port on each bridging device (except for the root device) which
incurs the lowestpath cost when forwarding a packet from that device to the root
device. Then it selects a designated bridging device from each LAN which incurs
the lowest path cos
to the root device
ll ports connected
designated ports, and disables all other ports. Network packets are therefore only
forwarded between root ports and designated ports, eliminating any possible
loops, and to provide backup links between switches, bridges or routers. This
allows the switch to interact with other bridging devices (that is, an STA-compliant
switch, bridge or router) in your network to ensure that only one route exists
between any two stations on the network, and provide backup links which
automatically tak
. t when forwarding a packet from that LAN
to designated bridging devices are assigned as designated A
ports. After determining the lowest cost spanning tree, it enables all root ports and
network loops.
Once a stable network topology has been established, all bridges listen for Hello
e
BPDUs (Bridge Protocol Data Units) transmitted from the Root Bridge. If a bridge
does not get a Hello BPDU after a predefined interval (Maximum Age), the bridge
assumes that the link to the Root Bridge is down. This bridge will then initiate
negotiations with other bridges to reconfigure the network to reestablish a valid
network topology.
RSTP is designed as a general replacement for the slower, legacy STP. RSTP
achieves must faster reconfiguration (i.e., around one tenth of the time required
by STP) by reducing the number of state changes before active ports start
learning, predefining an alternate route that can be used when a node or port fails,
itive to changes in the tre and retaining the forwarding database for ports insens
structure when reconfiguration occurs.
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