Enterprise voice and data networks are designed with physical component redundancy to eliminate the possibility of any single point of failure causing a loss of function for an entire switched network. Building a reliable switched network requires additional switches and redundant physical links. However, redundant Layer 2 switch topologies require planning and configuration to operate without introducing Layer 2 loops.
企業語音與資料網路在設計時會加入實體元件備援，以消除任何單一故障點導致整個交換式網路功能中斷的可能性。要建置可靠的交換式網路，需要額外的交換器與備援實體鏈路。然而，備援的第 2 層交換拓樸需要事先規劃與設定，才能運作而不會產生第 2 層迴圈。
Physical loops may occur in the network as part of a design strategy for redundancy in a switched network. Adding additional switches to LANs can add the benefit of redundancy. Connecting two switches to the same network segments ensures continuous operation if there are problems with one of the segments. Redundancy can ensure the constant availability of the network. However, when adding redundant physical links and additional switches, a physical loop is created and by spanning a single VLAN between connected switches a Layer 2 loop is also created.
在交換式網路中，做為備援設計策略的一部分，可能會產生實體迴圈。在區域網路（LAN）中新增交換器可帶來備援的好處。將兩台交換器連接到相同的網路區段，可確保在其中一個區段發生問題時仍能持續運作。備援可確保網路持續可用。然而，在新增備援實體鏈路與額外交換器時，會產生實體迴圈，而在連接的交換器之間跨接單一 VLAN，也會同時產生第 2 層迴圈。
Layer 2 LAN protocols, such as Ethernet, lack a mechanism for recognizing and eliminating endless looping of frames, as illustrated in the figure. Some Layer 3 protocols implement a Time to Live (TTL) or hop limit mechanism that limits the number of times that a Layer 3 networking device can retransmit a packet or limit how many Layer 3 devices a packet can traverse. Lacking such a mechanism, Layer 2 devices would continue to retransmit looping traffic indefinitely.
如圖所示，乙太網路等第 2 層 LAN 通訊協定缺乏辨識並消除框架無限循環的機制。部分第 3 層通訊協定實作了存活時間（TTL）或躍點限制機制，限制第 3 層網路裝置重新傳送封包的次數，或限制封包可經過的第 3 層裝置數量。由於缺乏這類機制，第 2 層裝置會不斷無限期地重新傳送循環中的流量。
Layer 2 loops affect performance in a switched LAN. A loop-avoidance mechanism solves these problems and STP was developed for that purpose.
第 2 層迴圈會影響交換式 LAN 的效能。迴圈避免機制可解決這些問題，而 STP 正是為此目的而開發的。