The node with the smallest id is selected the root bridge 2. Spanning tree protocol spanning tree port priority. Configuring the spanning tree protocol j web procedure. In the following example, we configure a dell powerconnect 5224 switch and a dell powerconnect 3348.
Spanning treeenabled switches go through a root election process based on bridge p rotocol. Configuration vlans, spanning tree, and link aggregation avaya ethernet routing switch 5000 series release 6. Example of a bridged network with a loop, and the minimum spanning tree with the loop removed. Stp spanning tree protocol explained with examples. Understanding and configuring spanning tree protocol stp on. Chapter 28 spanning tree protocols information about spanning tree protocols stp overview stp, the ieee 802. Below is an example of a bpdu sent out port fa03 by a switch with the default priority for vlan 1 of. The main purpose of stp is to ensure that you do not create loops when you have redundant paths in your network.
Thats to say it runs at the ethernet layer and is totally unrelated to dynamic ipbased routing protocols like rip, ospf or olsr which can take into. Highavailability networks with spanning tree and rapid. Otherwise, the port with the lowest root path cost will be the root port. A redundant link is an additional link between two switches. Rapid spanning tree protocol rstp introduction spanning tree protocol stp is a link layer network protocol that prevents bridge loops and flooding in local networks with redundant connections. Stp spanning tree protocol automatically removes layer 2 switching loops by shutting down the redundant links. Spanning tree protocol overview the plugandplay spanning tree protocol stp, a layer 2 protocol that ensures a loopfree topology in bridged lans, has been around for decades.
Rfc 7727 spanning tree protocol stp application of the. For example, all the edge weights could be identical in which case any spanning tree will be minimal. Figure 3 there are two types of bridge protocol data unit types. I have a new switch hp procurve 1810g and this switch is little bit diffrent as hp 281024 series,i need to active spanning tree protocol but i cant understand where is. Like alwaysit depends, lets take a look at an example. Spanning tree protocol stp stp often accounts for more than 50 % of the configuration, troubleshooting, and maintenance headaches in real world campus networks especially if they are poorly designed. To ensure a loop free topology, rapid spanning tree protocol rstp disables some connections leaving a single active path between any two devices. Understanding and configuring spanning tree protocol stp. Select the ports tab to configure the ports associated with this spanning tree. Spanning tree protocol stp spanning tree protocol stp was developed to prevent the broadcast storms caused by switching loops. Spanning tree also allows a network design to include spare redundant links to provide automatic backup paths. Spanning tree protocols help prevent broadcast storms 20. Switches running stp will build a map or topology of the entire switching network. On each switch, display the spanning tree table with the show spanningtree command.
The spanning tree map plugin display a graphical map of the bridgesswitches and help the adminitsrator to performs a real time monitoring of the links. By definition a tree is loop free stp does its work at layer 2 datalink of the osi model. Default port cost values port speed default port cost value 10mbps 100 100mbps 19. Stprstp configuration s12700 v200r010c00 configuration.
Stp overview stp is a layer 2 link management protocol that prov ides path redundancy while preventing loops in the network. To have a tree topology, you need bridges with more than two ports. A redundant link is usually created for backup purposes. Dell networking and cisco spanning tree interoperability. The spanning tree protocol stp is a network protocol that ensures a loopfree topology for any bridged ethernet local area network. Abcs of spanning tree protocol contemporary controls. Couper une liaison active entre 2 commutateurs ports actifs sur les 2. Im implementing hsrp on core switch in my network, but spanning tree always block one port on the layer 2 switch. On this map, all devices behaving as bridge are represented. Stp, rstp, and mstp page 3 overview of spanning trees overview of spanning trees the concept of the spanning tree protocol was devised to address broadcast storming.
Spanning tree protocol maintains a loopfree networkby pruning redundant links and monitors the stateof the network and will change the pathwaysto fit the current link conditions in orderto keep it. When you are adding a spanning tree, select a protocol name. Hu china telecom january 2016 spanning tree protocol stp application of the interchassis communication protocol iccp abstract the interchassis communication protocol iccp supports an inter chassis redundancy. Spanning tree protocol timing protocol is timer driven too short timers can give loops and instabilities too long timers can give long convergence. If you want to use the examples in this manual, you can use the load merge or the. In this article, i am going to explain all the terms, concepts and working of spanning tree protocol stp with the example, i have tried to clear all the concepts and doubts which usually rises in the spanning tree protocol so, if you are interested to know something more about spanning tree protocol keep reading this article till the end. S12700 v200r010c00 configuration guide ethernet switching this document describes the configuration of ethernet services, including configuring link aggregation, vlans, voice vlan, vlan mapping, qinq, gvrp, mac table, stprstpmstp, sep, and so on. Traditional spanning tree protocol, by implementation, takes about fifty 50 seconds to adapt and converge to topology changes. The spanning tree protocol stp is a network protocol that builds a loopfree logical topology for ethernet networks. This is because layer 2 ethernet frameshave no time to live or time out mechanismbuilt into the frame. Root selection varies depending on the bid of each switch in your lab resulting in varying outputs.
On the right is the minimum weight spanning tree, which has. To create a loopfree tree, bridges in the network exchange bpdus, and execute the spanning tree protocol as follows. Pdf spanning tree protocol simulation based on software. As the name suggests, it creates a spanning tree within a mesh network of connected layer2 bridges typically ethernet switches, and disables those links that are not part of the spanning tree, leaving a single active path between any two network nodes. This is necessary to avoid the potential bridging loop formed by the triangular architecture of the routers. Spanning tree protocol in layer 2layer 3 environments. The spanning tree protocol is primarily known today by its three most popular variants. The spanning tree protocol stp is a method for dynamically calculating the best spanningtree of a computer network with or without loops.
By default a cisco switch use pvst per vlan spanning tree but if we use the command show spanningtree with the default configuration the output is. Besides a mac address for each bridge, each port on each bridge must be identified. Spanning tree protocol is applicable for essentially any network that has two or more switches and. February 2006 page 3 spanning tree protocol info sheet. Just like every coin has two sides, a redundant link, along with several advantages, has some disadvantages. This document presents an overview of rapid spanningtree protocol rstp and multiple spanningtree protocol mstp and how to implement each. This section discusses the implementation of the spanning tree algorithm.
The basic function of stp is to prevent bridge loops and ensuing broadcast radiation. Root ports ports directly connected to the root bridge will be the root ports. Understanding spanning tree protocol this section describes how spanningtree features work. However, everything is viewed in relation to the root bridge. Bpdus are forwarded out all ports every two seconds. Intended audience this document is an implementation guide for deploying the recently ratified 802. Pvst, rapid spanning tree protocolrstp and multi spanning tree protocol mstp. Instructor spanning tree protocol is used ona local area network because in most casesswitches have redundant links for fault tolerance. The following image shows how the stp changes a physically looped topology into a virtually looped free topology.
All of the devices used in this document started with a cleared default configuration. Complex protocol that is generally poorly understood. The basic function of stp is to prevent bridge loops and the broadcast storms that. Port designations although bridges do not need mac addresses to operate, a mac address is needed to identify bridges in the spanning tree protocol. When you have 20 vlans, it means there are 20 instances of spanning tree. Spanning tree also allows a network design to include backup links providing fault tolerance if an active link fails as the name suggests, stp creates a. Lecture notes on spanning trees carnegie mellon school. Although the cisco switches in this example use cisco ios version 12. With iosbased switches you can check what version you are running with the command show spanningtree summary. If your network is live, make sure that you understand the. Spanningtree protocol is a link manage ment protocol that provides. Stp switches exchange bridge protocol data units bpdus to build the topology database.
To view the information about the stp operation, you can use the show spanningtree command from the privilegedexec mode. Spanning tree protocol stp is standardized as ieee 802. Radia perlman spanning tree protocol eliminate edges until the result is loop free actually add edges without creating loops this transforms the graph into a tree changes in the topology cause the tree to change a root bridge is elected as the root of the tree example spanning tree. Prerequisites requirements there are no specific requirements for this. The basic function of stp is to prevent bridge loops and the broadcast radiation that results from them. Read how do all the operations happen and what are the chief components of the same. Spanning tree protocol this document descibes spanning tree protocol stp in a wireless environment. The information in this document is current as of the date on the title page.
The spanning tree protocol stp is designed to prevent layer 2 loops. This means that each vlan is mapped to a single spanning tree instance. The spanning tree algorithm itself is defined by the ieee standard 802. Spanningtree protocols user guide juniper networks. Spanning tree protocol stp is a layer 2 protocol that runs on bridges and switches. Spanningtree protocol the spanning tree protocol stp is a network protocol that ensures a loopfree topology for any bridged ethernet local area network. Mstp is configured on the three routers so the set of vlans has an independent, loopfree topology. The spanning tree protocol stp enables loopfree, redundant bridging paths by. Spanning tree protocol stp determines the least cost path from the root bridge to other nodes in the networks. Spanning tree protocol spanning tree overview 1461 the following sections describe spanning tree configuration parameters. In order to provide this desired path redundancy, as well as to avoid a loop condition, stp defines a tree that spans all the switches in an extended network. The problem is that when we create redundancyat a layer 2 level of our networks,we create loops that traffic will traverse indefinitely. In simple words, whenever a topology change occurs in the network e. Configure the spanning tree protocol on all three routers.