One
of the biggest issues that network administrators face when designing a switched
network is the prevention of loop. In network topology changes always happen
and if in case a loop forms then the traffic that passes through the affected switches
can easily drain out the entire bandwidth allocated to these switches. There
are several solutions to handle such issue but the best way to prevent the
formation of loops in a switched network is to deploy the Spanning Tree
Protocol (STP).
What is Spanning Tree Protocol?
STP
is a standardized solution provided by IEEE which helps to prevent loop
formation in data networks. It was invented by Dr. Radia Perlman.
In a
switched network all the switches generate data messages, which are known as Bridge
Protocol Data Units (BPDUs). The working principle behind the exchange of BPDUs
is that switches will be able to indentify redundant paths in a network by
applying the STP algorithm and ensure that no loops are formed. The STP algorithm
identifies all active redundant links and blocks them to prevent the formation
of loops. The entire working of Spanning Tree Protocol can be broken down into
three easy steps
Step
1: All STP enabled switches in a network elect a root bridge. All the switches
exchange messages (BPDUs) among themselves and elect a root bridge. This
process is known as Root Bridge Election.
Step
2: The second step is known as Root Port Election. Once all switches have
elected a Root Bridge, the next part is to decide which port of a switch will
communicate with the Root Bridge.
Step
3: The final step is to have only one
active path left open in every part of the network and bypass the creation of a
loop. This is known as Designated Port Election.
What is Spanning Tree Protocol Important?
STP’s
importance lies in the fact that it provides data redundancy to all devices in
a network. It means the every connection has a backup so that it is able to
send data in case the primary connection is down. However, only one path is
open at a time. In the event that the open path experiences any error another
path will open up ensuring constant flow to data to all devices. STP also
prevents the formation of bridge loops so that the entire bandwidth allocated
doesn’t get drained. Loops occur when there are multiple open paths for data
transmission which can result for errors in data processing and forwarding.
With STP only one path is open at a time thus eliminating loops.
Topology
changes happen all the time in any network and more so in large networks. But
network failure even for a few seconds can bring about serious consequences especially
for multinational organizations. Spanning tree protocol ensures that the
network keeps running without any data loss between devices and makes high
availability of a network possible. Conventional STP takes around 50 seconds to
adapt to any changes in the network but for large networks this is a lot of
inactivity time. Currently a new upgraded version of STP is available called
Rapid Reconfiguration or Fast Spanning Tree which cuts down on convergence time
and helps recover quickly from network failure or session timeouts.
