Spanning Tree Protocol (STP)
In Layer 2 domain, redundancy is an important case. To provide redundant links, multiple connections are done between switches. But this redundancy mechanism can cause an undesirable situation that is called “L2 Loop”. To provide L2 redundancy and to avoid L2 loops, Spanning Tree Protocol (STP) has been developed.
During the development period, various versions of STP has been introduced. Different standards has been created beside Cisco specific versions. These STP versions are :
• STP (Spanning Tree Protocol) – 802.1D
• RSTP (Rapid Spanning Tree Protocol) – 802.1W
• PVST+ (Per VLAN Spanning Tree Plus) – Cisco Proprietary
• Rapid PVST+ (Rapid Per VLAN Spanning Tree Plus) – Cisco Proprietary
• MST (Multiple Spanning Tree) – 802.1s
In this article, mainly we will focus on STP (802.1D).
Redundant Layer 2 Problems
Redundancy is an important term for a network. Layer 2 Redundancy is also important but need more caution. Without a mechanims like STP, Layer 2 Redundancy mechanisms can cause the below problems:
• Layer 2 Loops and Broadcast Storms
• MAC Address Instability
• Duplicate Frame Transmission
Let’s talk about each of these Layer 2 Redundacy problems.