Basic concepts on Spanning Tree Protocol(STP)
STP (Spanning tree protocol) is very simple protocol used in LAN technology to avoid loops in the redundant network. Though it may look very simple, I read many documents to understand how it works and why it is required. However, I hardly could understand it clearly until and unless i worked on it. Yes, we can get many documents/pdfs in the internet but those mayn’t provide you sufficient information to understand it. In this article I am trying to give very clear concept on STP so that one needn’t struggle much to understand it better.
Well, before we begun with STP, let me tell you some special characteristics of switches.
1. Actual Communication at layer-2 happens based on MAC address.
2. Switches make the forwarding decision based on the destination MAC address.
3. Switches learn the MAC addresses of devices on their port so that data is properly forwarded to the destination.
4. Switches use source MAC address to learn where the devices are and enter the information in the MAC address table.
5. Incase switches MAC address table doesn’t contain the destination address associated with the port then switches flood the unknown unicast to all ports except the incoming one.
6. Once Switches learn the MAC address of the destination then unicast frames will be forwarded.
What kind of LAN topology is in use today?
To ensure the quality and reliability, practical LAN topologies are made redundant. And hence we can achieve fault tolerance. That is if one path in the topology fails, packets takes another path. Having said that redundant topology results into many problems in LAN network.
What are the problems of redundant topologies?
- Broadcast storm
- Multiple frame transmission
- Wrong MAC address table
Why do above problems occur?
Unlike IP, in the layer-2 header there is no TTL (time to live).Which means the packets get dropped by node after crossing certain hops. As we don’t TTL in Layer-2 header, frames get replicated in network and keep on looping in the network resulting bandwidth crisis in the network.
How exactly above problems occur?
--Yet to update
How to overcome these problems of redundant network?
Here we go;STP is the protocol which overcomes all the problems identified above in the network. This solution is to allow physical loop (redundant) topology with the loop free logical topology.
How does STP function?
--Yet to update
Comments