What is STP and how does it work?
The operation of STP is as follows: STP enabled switches exchange BPDU messages between them to agree upon the "root bridge;" the process is called Root Bridge Election. Once the root bridge is elected, every switch has to determine which of its ports will communicate with the root bridge.
Where should STP be activated?
Therefore, great caution needs to be taken where to activate STP. As a rule of thumb STP should be disabled on access ports.
Should STP be enabled or disabled on ports?
As a rule of thumb STP should be disabled on access ports. To do that you should set all access ports as portfast (meaning that these ports should be put immediately back in forwarding state and avoid the 50 seconds of blackout) and also enable bpdufilter on those ports so that they do not participate in STP.
What is STP (spanning protocol data units)?
As the name implies, STP, spans all switches in a network or subnet. All switches generate and process data messages called Bridge Protocol Data Units (BPDUs). The basic idea behind the exchange of BPDUs is for switches to identify redundant paths and by using the Spanning Tree algorithm, to ensure that there is no loop path in the network.
What protocol is used to prevent switching loops?
the Spanning Tree algorithmAll switches generate and process data messages called Bridge Protocol Data Units (BPDUs). The basic idea behind the exchange of BPDUs is for switches to identify redundant paths and by using the Spanning Tree algorithm, to ensure that there is no loop path in the network.
How does STP prevent a network storm?
To prevent broadcast storms, the Spanning Tree Protocol (STP) eliminates redundant paths by placing only one switch port in forwarding mode and placing all other ports connected to the same segment in blocking mode.
How does STP work in networking?
Spanning Tree Protocol (STP) Operations The Spanning Tree Protocol (STP) is responsible for identifying links in the network and shutting down the redundant ones, preventing possible network loops. In order to do so, all switches in the network exchange BPDU messages between them to agree upon the root bridge.
What does STP do in networking?
Spanning Tree Protocol (STP) is a Layer 2 network protocol used to prevent looping within a network topology. STP was created to avoid the problems that arise when computers exchange data on a local area network (LAN) that contains redundant paths.
How does STP work?
STP works on Ethernet LAN’s. STP prevents loops, selects the best LAN path, and provides redundancy if a link fails. Part of selecting the best path is calculating the best path to the root switch is calculating the link costs, based on the speed of the links. A port can be in any of 5 states with STP – blocking, listening, learning, forwarding, ...
How to avoid a loop in LAN?
A loop in your LAN can bring down the whole network. You can avoid a loop by using Spanning Tree protocol (STP). Let’s find out what Spanning Tree is, how it works, and how it can save your day by preventing a loop on your network.
What is a Spanning Tree?
What is Spanning Tree? The Spanning Tree protocol is a networking standard, as defined by the IEEE in the 802.1d standard. The purpose of Spanning Tree is to prevent loops in the LAN and to select the fastest network links, if there are redundant links in the network. In the event that a link in the network goes down, ...
What are the criteria for a Spanning Tree?
The three criteria Spanning Tree uses to decide if an interface should be in forwarding state are: All interfaces on the root bridge are put in forwarding state. For other bridges that are not the root bridge, the port that is closest to the root bridge is put in forwarding state. The bridge with the lowest administrative distance to ...
Can you use multiple links in Spanning Tree?
Spanning Tree cannot use multiple links to the same destination. There is no load-sharing feature with Spanning Tree. Any redundant link that is not as preferred is blocked (essentially shut down) until the primary link goes down. Because Spanning Tree is a complex protocol, this article won’t cover every possible feature.
Switching 101
To understand what a switching loop is and how it happens, it’s necessary to have a basic grasp of network switching.
How loops happen
During normal operation, switches forward traffic along a path from one destination to another hop by hop. However, when switches are connected in such a way that it creates a loop, network traffic can get stuck in this loop and never reach its destination.
Troubleshooting a switching loop
Although protocols exist to help prevent switching loops, they are not always implemented. When they are, they are sometimes not implemented correctly. As a result, knowing how to trace the source of a loop manually is a good skill for an administrator to have.
Preventing switching loops
As the saying goes, “an ounce of prevention is worth a pound of cure.” Knowing how to identify the source of a switching loop is a good skill to have, but ideally, a network administrator will want to leverage protocols and technologies that prevent switching loops from occurring.
Conclusion
Switching loops can take down an entire network. It is important for network administrators to understand how they happen, because understanding them gives administrators a better grasp of how network traffic flows and the ability to troubleshoot loops to avoid frustration.
