A redundant link is usually created for backup purposes. In the first example shown in figure 9, we will assume that bridge 1 has the lowest bridge id, and that bridge 6 has a higher path cost than bridge 4. Stp is on by default, but it only really comes alive when we have two or more switches interconnected with each other. Download pdf stp spanning tree protocol step by step configuration tutorial when sw3 start receiving inferior bpdus at its interface from sw2, switch3 would ignore the inferior information until the bpdus stored with the blocked port expires max age timer 20 seconds. I think it is a good idea to look at the same concepts using real equipment. Spanning tree protocol in layer 2layer 3 environments. It is quite useful and should be enabled on the switch interfaces. Spanning tree protocol interface states by shabeeribm. Mstp uses bpdus to exchange information between spanningtree compatible devices, to prevent loops in each msti multiple spanning tree instances and in the cist common and internal spanning tree, by selecting. Hi guys, this post got awarded best publication at the cisco support community. Before we talk about spanning tree protocol, lets organize the different variants of stp. Spanningtree protocol, or stp, prevents switching loops in the layer 2 portion of our network. Cisco didnt change the spanning tree protocol, but they extended it so that each vlan can have a separate spanning tree instance pvst. Lets see how we can select the root bridge for spanning tree protocol.
However, without some practice its just academic knowledge. Just like every coin has two sides, a redundant link, along with several advantages, has some disadvantages. Spanning tree protocol explained step by step youtube. Abbreviated stp, a link management protocol that is part of the ieee 802. Loops occur when there are alternate routes between hosts. Stp was created to avoid the problems that arise when computers compete for the ability to use the shared telecommunications path on a local area network. Disable the spanning tree on ports ex 01 and ex 02. Stp spanning tree protocol step by step configuration. Second, when redundant loops are planned on a network, stp deals with remediation of network. The spanning tree protocol is primarily known today by its three most popular variants. Tree protocol is a robust and scalable solution to redundancy in a layer 2 network, the single logical link does. What is happening at this moment is that spanning tree is determining the state of the. The basic function of stp is to prevent bridge loops and the broadcast radiation that results from them. The spanning tree protocol stp is a network protocol that builds a loopfree logical topology.
Multiple spanning tree protocol or multiple instance spanning tree protocol multiple instances of vlan mapped to 1 stp tradeoff between ieee 802. Spanning tree protocol overview presented by arash foroughi iran, november 2015 2. The industry feared extending the influence that cisco has over networking, and it created a competing protocol, vrrp, which really does the same thing that hsrp does. Because spanning tree protocol operates on layer 2 of your network, you can enable this feature without any impact to firebox performance. Tree topology to avoid loops we need a tree topology consisting of a root, a succession of branches and then leaves. Spanning tree protocol networking mcq questions and. Spanning tree also allows a network design to include spare redundant links to provide automatic backup paths if an active link fails. So therefore, if there is a tie in our value with spanningtree protocol, there has to be a tiebreaker mechanism. Stp will identify if there are any loops, and then disable or block. A port can never be both a designated port and a root port. The other requirement is that all leaves are connected. Ports on the root bridge are never placed in a blocking state. This tutorial explains what the stp protocol is and how it removes loops from the network. In this article, we will learn how stp prevents loops, and how it handles the layer 2 convergence.
Spanning tree protocol timing protocol is timer driven too short timers can give loops and instabilities too long timers can give long convergence times until network reaches a stable spanning tree configuration proto id 2 root id 8 ver 1 bpdu type 1 flags 1 root path cost 4 bridge id 8 port id 2 msg age 2 max age 2 hello time 2. Introduction to spanningtree spanningtree is a protocol that runs on our switches that helps us to solve loops. 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. To create a loopfree tree, bridges in the network exchange bpdus, and execute the spanning tree protocol as follows. 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 spanning tree that. Root selection varies depending on the bid of each switch in your lab resulting in varying outputs. You might have noticed that when you plug in a cable to cisco switches the led above the interface was orange and after a while became green. Vlan0005 spanning tree enabled protocol ieee root id priority 32773 address 00. Perlman devised a method by which bridges can obtain layer 2 routing utopia. Complex protocol that is generally poorly understood. Downstream bridge blocks all nonedge designated ports and send. Lesson 21 spanningtree protocol in practice previous post was designed to present in a nutshell the stp operation.
All switch ports in the lan where stp is enabled are categorized. First, it prevents problems caused by loops on a network. Learn spanning tree protocol mcq questions and answers with easy and logical explanations for various competitive examination, interview and entrance test. At this time there were no switches yet, only bridges, but because bridges and switches. Avoids loops by reducing network connectivity reacts to changes in the network topology either good news or bad news is completely transparent to the user stp implements fault tolerance at data link level. Media in category spanning tree protocol the following 21 files are in this category, out of 21 total.
For more information about the default spanning tree protocol settings, see configure spanning tree protocol settings in the cli. Source mac addresses are repeatedly seen coming from different ports. Configuring ports to be edge ports portfast in cisco, reduces the time to establish a connection to just a few seconds. Switches running stp will build a map or topology of the entire switching network. Spanning tree protocol this document descibes spanning tree protocol stp in a wireless environment. The original stp was developed by radia perlman while working for dce back in 1990. Spanning tree protocol spanning tree overview 1461 the following sections describe spanning tree configuration parameters. Spanning tree protocol configuration examples and technotes.
The basic function of stp is to prevent bridge loops and ensuing broadcast radiation. Spanning tree protocol runs on switches and bridges on a lan. Just fyi, you will be asking them to implement rapid spanning tree protocol 802. Even if a loop exists due to cable connection, one of the ports connecting the cable is disabled by the stp. Spanning tree protocol or stp for short was created to solve these kinds of problems. Understanding issues related to intervlan bridging pdf. Indeed there is and an example would be the spanning tree protocol. Spanning tree protocol stp is a layer 2 network protocol used to prevent looping within a network topology. Spanningtree protocol enhancements using loop guard and bpdu skew detection features. The multiple spanning tree protocol mstp and algorithm, provides both simple and full connectivity assigned to any given virtual lan vlan throughout a bridged local area network. Abcs of spanning tree protocol contemporary controls. In the ccna exam, stp and its derivatives are an important topic.
The spanning tree protocol is a link management protocol that is designed to support redundant links while at the same time preventing switching loops in the network. Presentation aqseamanmergedspanningtreeprotocols1108. Example of a bridged network with a loop, and the minimum spanning tree with the loop removed. Root bridge is the switch that has lowest bridge id. Figure 2 shows an example of this process in which requests from host 2 are directed to the switch that acts as the. Spanning tree protocol stp was developed before switches were created in order to deal with an issue that occurred with networks that were implementing network bridges. Many people struggle with stp so in this video, we try to break it down as much as possible. Radia perlman, distinguished engineer at sun microsystems. The spanning tree protocol stp is a network protocol that ensures a loopfree topology for any bridged ethernet local area network. When too many computers try to send at the same time, overall network performance is affected and can bring all traffic to a near. Bpdu packets are send to the network each two seconds.
Understanding spanning tree protocol this section describes how spanningtree features work. Spanning tree enabled switches go through a root election process based on bridge p rotocol data unit. Enablingloopprotectionforspanningtreeprotocols227 configuringloopprotectionforaspanningtreeinstanceinterface228. To tie this all together, lets look at two examples of the spanningtree protocol in action. Introduction to spanning tree protocol contemporary controls. Stp spanning tree protocol explained with examples. Stp spanning tree protocol automatically removes layer 2 switching loops by shutting down the redundant links. The bridge supports both pervlan spanning tree pvst and a single 802. This protocol is a layer two layer two data link layer protocol that is associated with switches and bridges. To have a tree topology, you need bridges with more than two ports. On each switch, display the spanning tree table with the show spanning tree command. Spanning tree protocol stp is a big topic on the ccna exam. February 2006 page 3 spanning tree protocol info sheet.
Therefore, the tree is free of loops that can cause havoc in a network. Spanning tree protocol stp spanning tree protocol stp was developed to prevent the broadcast storms caused by switching loops. The leaves represent end stations, and there is one and only one path from a leaf to another leaf. Overview of spanning tree protocol linkedin slideshare. Using the spanning tree algorithm, stp provides path redundancy while preventing undesirable loops in a network that are created by multiple active paths between stations. Bridge id is the combination of the priority which is a value between 0 61440, default 32768 and mac address. 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. A redundant link is an additional link between two switches.
Spanning tree protocol stp determines the least cost path from the root bridge to other nodes in the networks. When you connect two or more layer 2 devices, an election is run to designate the root bridge. The spanning tree protocol stp is a network protocol that builds a loopfree logical topology for ethernet networks. Figure 3 there are two types of bridge protocol data unit types. Spanning tree protocol interface states sysnet notes.
Predominantly switches really as bridges have fallen by the wayside in terms of usage. The golden rule of spanningtree protocol is lower is better. Solved is there a reason for spanning tree to not be. 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. It effectively eliminates logical loops, while allowing physical loops to still exist. Spanningtree protocols user guide techlibrary juniper. The election decides which switch will become the root bridge, as well as the. Stp works in a broadcast domain therefore each vlan has its own spanning tree. Stp overview stp is a layer 2 link management protocol that prov ides path redundancy while preventing loops in the network. Spanning tree protocol basics the ieee defines the spanning tree protocol that provides a loop free redundant network topology by placing certain ports in the blocking state.
1611 957 444 978 874 1347 566 1624 781 422 765 339 569 88 1386 680 1616 150 1142 1629 648 903 1516 448 622 430 379 937 1588 583 921 1263 122 1043 1409 1074 1412 487 298 1393 1416 834 788