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Spanning Tree (SPT)

The Spanning Tree Protocol (STP) is a network protocol developed to prevent loops in networks with multiple devices or switches. Loops can occur when multiple connections exist between switches, which can lead to problems such as broadcast storms and network congestion.

Goal & Purpose​

The Spanning Tree Protocol (STP) prevents Layer 2 loops in switched networks. A loop occurs, for example, due to accidentally connected switch ports or redundant cabling.


Goal of STP:​

  • Loop-free topology

  • Automatic blocking of redundant connections

  • Automatic recalculation in case of link failures


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Why STP is important for larger networks:​

Without STP, a single LAN loop can cause the following problems:

  • Broadcast storms (Network overload, up to 100% CPU/load on switch & router)

  • MAC flapping (MAC addresses jump between ports)

  • Total network standstill (communication no longer possible)

  • Centro Business can crash or hang


Activate Spanning Tree​

  • In the router portal of the Centro Business 3.0, under the tab Network ➜ Basic settings
  • Activate STP (Default is OFF)

Key points to consider​

1. Redundant cabling​

If two switches are connected via more than one cable → STP must be activated. Otherwise, a Layer 2 loop is created immediately.

2. Define Root Bridge​
  • Every STP network has exactly one Root Switch.

Best Practice:

  • The most powerful & central switch should be Root (e.g., Core Switch)

  • Switches at the edge (Access) should NOT become Root

  • Set priority specifically (e.g., 4096 for Core Switch)

3. Connection to Centro Business​

The Centro Business itself is not an STP Root. STP must be properly configured on the connected switches, otherwise:

  • Ports go into blocking

  • Network unstable

  • DHCP/VoIP/Internet intermittent

4. Ports in Edge/Access Mode​

For end devices (servers, PCs, printers, WLAN APs):

  • Configure port as Edge/PortFast so that it becomes active immediately. Otherwise, the port takes 15–30 seconds (STP Learning/Listening).

5. VLANs & Trunk Ports​

If a VLAN trunk is running between switches:

  • Configure STP identically everywhere

  • Identical VLANs on both sides, otherwise inconsistent STP topology


Limitations​

  • Not available with BNS/EC-S contract

FAQ - Spanning Tree (SPT)​

Which SPT protocol is supported?

Only the Spanning Tree Protocol 802.1D is supported by the Centro Business 3.0.

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