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you can also visit this link
www.en.wikipedia.org/wiki/Spanning_tree_protocol

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Posted by waqasahmad

For detail follow the link www.en.wikipedia.org/wiki/Spanning_tree_protocol

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Posted by HamidAliKhan

The functions of a switch were Layer 2 Loop removal. The Spanning Tree Protocol (STP) carries out this function. STP is a critical feature; without it many switched networks would completely cease to function. Either accidentally or deliberately in the process of creating a redundant network, the problem arises when we create a looped switched path. A loop can be defined as two or more switches that are interconnected by two or more physical links.

Switching loops create three major problems:
• Broadcast storms - Switches must flood broadcasts, so a looped topology will create multiple copies of a single broadcast and perpetually cycle them through the loop.
• MAC table instability - Loops make it appears that a single MAC addresses is reachable on multiple ports of a switch, and the switch is constantly updating the MAC table.
• Duplicate frames - Because there are multiple paths to a single MAC, it is possible that a frame could be duplicated in order to be flooded out all paths to a single destination MAC.

All these problems are serious and will bring a network to an effective standstill unless prevented.

Other than simple error, the most common reason that loops are created is because we want to build a redundant or fault-tolerant network. By definition, redundancy means that we have a backup, separate path for data to follow in the event the first one fails. The problem is that unless the backup path is physically disabled - perhaps by unplugging it - the path creates a loop and causes the problems mentioned previously. We like redundant systems; we do not like loops and the problems they cause. We need a mechanism that automatically detects and prevents loops so that we can build the fault-tolerant physical links and have they become active only when needed. The mechanism is called the Spanning Tree Protocol; STP is a protocol that runs on bridges and switches to find and block redundant looped paths during normal operation. Spanning Tree was originally developed by the Digital Equipment Corporation (DEC), and the idea was adopted and modified by the IEEE to become 802.1d. The two are incompatible, but it is exceedingly rare to find a DEC bridge these days, so the incompatibility is not usually a problem.

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Posted by thomas

Please visit:
www.en.wikipedia.org/wiki/Spanning_tree_protocol

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Posted by sagitraz