Skip to main content

Spanning Tree (STP)

The Spanning Tree Protocol (STP) prevents Layer 2 loops in switched networks by automatically blocking redundant connections and recalculating when link failures occur. A loop can be caused by accidentally connected switch ports or redundant cabling, leading to broadcast storms, MAC flapping and complete network standstill.

tip

STP is exclusively available on the Centro Business 3.0.

Why STP is important in 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 jumping between ports)
  • Complete network standstill (no communication possible)
  • Centro Business may crash or hang

Activate Spanning Tree​

In the router portal of the Centro Business 3.0 under Network → Basic Settings:

  • Activate STP (default is OFF)

Best Practices​

1. Redundant cabling​

If two switches are connected by more than one cable → STP must be activated. Otherwise a Layer 2 loop occurs immediately.

2. Define Root Bridge​

Every STP network has exactly one Root Switch.

  • The most powerful and central switch should be Root (e.g. Core Switch)
  • Edge switches (Access) should NOT become Root
  • Set priority deliberately (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 it becomes active immediately
  • Otherwise the port takes 15–30 seconds (STP Learning/Listening)

5. VLANs & Trunk ports​

When VLAN trunk is running between switches:

  • Configure STP identically everywhere
  • Identical VLANs on both sides, otherwise inconsistent STP topology

Limitations​

  • Only available on Centro Business 3.0
  • Not available with BNS/EC-S contract
  • Only 802.1D is supported (no RSTP/MSTP)

FAQ - Spanning Tree (STP)​

Which STP protocol is supported?

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

What happens if STP is disabled and a loop occurs?

Without STP, a loop immediately causes a broadcast storm. The network becomes overloaded within seconds and the Centro Business may crash. Restarting the router alone does not solve the problem — the loop must be physically removed.

info

Is something missing? Give us your feedback!

Help us improve the CB Guide. Let us know what content you are missing or what we can optimise.

Send feedback

Last updated on