STP

When the design requires some LAN switches, network engineer generally include a redundant LAN segment between these switches.

The goal is simple, the switches are likely to fail in operation, or there is the possibility of the cable was disconnected or unplug redundant so that the existence of this segment, the network service can still be running even though there are obstacles above.

LAN with redundant link that allows the frame looping endlessly in the network.

These looping frames that cause performance problems on the network.

STP is a protocol contained in the OSI layer 2 functions to ensure the absence of loops in the network topology LAN. STP allows a network to include links that are free (extra) to provide automatic backup if the primary link being active failed, without danger of the loop on the bridge, enable or disable this backup link manually. Bridge loops must be avoided. because it could create a network flooding occurs.
Excess Spanning Tree Protocol (STP)
1. Avoiding Traffic with mesegmentasi high bandwidth access through the switch
2. Provides Backup / stand-by path to avoid loops and switches the failed / failing
3. Prevent looping

Common problems can be alleviated by the Spanning Tree Protocol is a broadcast storm. Broadcast storm caused a lot of broadcast (or multicast or unicast-destination unknown) in the loop on the network continuously. This will create a link that is not useful (because of the dual link between the bridge / switch) and will significantly affect the performance of end-user's computer because of too many existing broadcast process.

Broadly speaking, Spanning Tree Protocol work this way:
Determine the root bridge.

Root bridge of the spanning tree bridge ID is a bridge with the smallest (lowest). Each bridge has a unique identifier (ID) and a priority number which can be configured. To compare two bridge ID, priority number than the first time. If the priority number between the two bridges are the same, then that will be compared next is the MAC addresses. For example, if switches A (MAC = 0000.0000.1111) and B (MAC = 0000.0000.2222) have the same priority number, say 10, then switch A which will be selected to be the root bridge. If the network admin to switch B is to become root bridge, then the priority number switch B must be smaller than 10.

Determine the least cost paths to the root bridge.

Spanning tree that has been calculated to have the property that is the message from all devices connected to root bridge with traverse with the lowest cost path, the path of the tool to the root has the lowest cost of all paths of the tool to root.Cost of traversing a path is number of cost-cost of the existing segments in the path. Different technologies possessed a different default cost for the network segments. Administrators can modify the cost to visitor network segment that feels important.