Spanning Tree Protocol (STP, IEEE 802.1D) is a layer-2 protocol that allows a switched network to have redundant physical links without creating loops. Switches exchange messages called BPDUs, elect a root bridge and then place some ports into a blocking state, leaving a loop-free tree.
Why it matters
Ethernet frames have no hop limit like IP's TTL, so a loop lets broadcast frames circulate and multiply endlessly, a broadcast storm that can bring down a whole network in seconds. STP lets you wire extra cables for redundancy: if an active link fails, a blocked port is unblocked and traffic resumes. The original protocol took tens of seconds to reconverge; Rapid STP (802.1w) usually recovers within a second or so, and per-VLAN variants are common.
Example
Three switches are cabled in a triangle. The one with the lowest bridge priority becomes root. The link between the two non-root switches farthest from the root has one end blocked. If the link between a switch and the root is cut, the blocked port moves to forwarding.
Common mistakes
- Leaving root election to chance; set the bridge priority on the intended core switch.
- Plugging a desktop switch into two wall ports without STP protection such as BPDU guard.
- Disabling STP to "fix" a slow port instead of using PortFast on edge ports.
Related
Get notified when this term updates
Plus occasional practical tips on uptime and monitoring, nothing else. Unsubscribe anytime.
यह पेज सामान्य जानकारी है, जिसे हमारी संपादकीय टीम ने लिखा है और दस्तावेज़ीकरण बदलने पर अपडेट किया जाता है। सर्वर और प्रदाता अलग-अलग होते हैं, इसलिए बदलाव पहले सुरक्षित तरीके से जाँचें। देखें: संपादकीय नीति और अस्वीकरण.