In this spanning tree protocol tutorial, i will present in simplest terms the operation of stp and indicate how. We will also see how the spanning tree protocol reacts when the topology changes. This can be on a single switchor amongst several switches that are trunked together. 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. The mst instances combine with the ist at the boundary of the. Spanning tree protocol understand stp principles, redundant. Aruba vsf and cisco vss combine multiple switches into a single logical entity. When you connect two or more layer 2 devices, an election is run to designate the root bridge. Spanning tree protocol concepts 45 in many ways, those last two paragraphs sum up what stp does. Spanningtreeinstanceinterfaceshavepriorities36 whatisspanningtreeinstanceinterfacecost.
To combine rstp with mrp, you perform the following steps in sequence. Voiceover a switched networksgreatest enemy is a loop. Stp spanning tree protocol automatically removes layer 2 switching loops by shutting down the redundant links. Pvst uses 1 stp for each vlan, mst uses 1 stp for multiple vlans so we have a mismatch here. A redundant link is an additional link between two switches. Redundancy configuration user manual tcsesm, tcsesme. Understanding and configuring multiple spanning trees cisco. Newest spanningtree questions feed subscribe to rss newest spanningtree questions feed to subscribe to this. 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. On the new version of the cisco ccent 100101, cisco icnd2 200101 and ccna 200120 exams cisco has made the questions much, much, harder than previous versions of the ccna exam.
This creates a loopfree logical topology, so that a broadcast storm cannot occur. Abcs of spanning tree protocol contemporary controls. The interchassis communication protocol iccp supports an inter chassis redundancy mechanism that is used to support high network availability. This is accomplished by placing abstract the spanning tree protocol that is the basis for the ieee standard 802. Spanning tree was great when it came out in 1990, but there have been a number of changes to networking and a number of changes to spanning tree through the years.
The spanning tree protocol stp is a network protocol that ensures a loopfree topology for any bridged ethernet local area network. This standardized solution is called spanning tree protocol stp. The person behind the invention of spanning tree protocol is radia perlman. Cisco home page for the spanningtree protocol family discusses cst. The redundancy configuration user manual contains the information you need to select a. Spanningtree protocol stp has nowadays been implemented by most manufacturers in order to avoid loops in bridged networks.
Spanning tree follows a strict set of rules which when learnt, will allow you to answer any stp questions you get. 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. The basic function of stp is to prevent bridge loops and ensuing broadcast radiation. Arista switches support rapid spanning tree, multiple spanning tree, and rapidper vlan spanning tree protocols. It is quite useful and should be enabled on the switch interfaces. Because spanning tree protocol operates on layer 2 of your network, you can enable this feature without any impact to firebox performance. As with traditional shared ethernet, transparent bridges inherently lack the capability to provide redundancy. Stp will identify if there are any loops, and then disable or block.
Without this protocol our lans would rapidly become congested, with frames looping throughout the network infinitely, making network devices unstable. Stp overview stp is a layer 2 link management protocol that prov ides path redundancy while preventing loops in the network. When the bridged lan topology changes, a new spanning tree is constructed. Switches running stp will build a map or topology of the entire switching network. Hi guys, this post got awarded best publication at the cisco support community. 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. A dependable alternative to the spanning tree protocol. Routing protocols like ospf and eigrp are much faster than spanningtree when they have to deal with changes in the network. Aug 29, 2017 spanning tree follows a strict set of rules which when learnt, will allow you to answer any stp questions you get. To have a tree topology, you need bridges with more than two ports. The spanning tree protocol stp is a network protocol that builds a loopfree logical topology for ethernet networks. Dec 22, 2012 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. The assignment of forwarding and blocking ports are same in both stp and rstp, the main reason to use rstp is to overcome the convergence time and therefore it supposes the spanning tree best practice.
Spanning tree protocol stp stp detects and breaks network loops and provides backup links between switches, bridges or routers. Spanningtree protocols user guide juniper networks. Pvst uses 1 stp for each vlan, mst uses 1 stp for multiple vlans so we have a. If all of the edges of g are also edges of a spanning tree t of g, then g is a tree and is identical to t that is, a tree has a unique spanning tree and it is itself. Why do we use stp spanning tree protocol or rstp rapid spanning tree protocol when packets are not routed optimally. Spanning treeinstanceinterfaceshavepriorities36 whatisspanningtreeinstanceinterfacecost. Understanding issues related to intervlan bridging pdf. By default a cisco switch use pvst per vlan spanning tree but if we use the command show spanning tree with the default configuration the output is. To keep up with the speed of these routing protocols another flavor of spanningtree was createdrapid spanningtree. Pdf formal specification of spanning tree protocol using acp. The spanning tree protocol stp inserts a mechanism into the ethernet transparent bridge environment to dynamically discover the network topology and ensure only one path through the network. Understanding spanning tree protocol this section describes how spanningtree features work. Spanning tree protocol this document descibes spanning tree protocol stp in a wireless environment. The intel pro set ieee rapid spanning tree protocol rstp can be used alongside 802.
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. The latest version of spanning tree is rstp, this is 802. The multiple spanning tree protocol mstp is an stp variant that allows multiple and independent spanning trees to be created over the same physical network. Understanding spanning tree page 2 learn the basics of the spanning tree protocol stp and its drawbacks and alternatives with the enp primer. Radia perlman, distinguished engineer at sun microsystems.
Mtrees merge with the ist at the boundary of the mst region and form the cst. The spanning tree protocol performs this magic by disabling certain connections between switches. The spanning tree protocol run my experiment on geni. Introduction to spanning tree protocol by george thomas, contemporary controls introduction in an industrial automation application that relies heavily on the health of the ethernet network that attaches all the controllers and computers together, a concern exists about what would happen if the network fails. The multiple spanning tree protocol mstp, originally defined in ieee. It should take about 1 hour to run this experiment. Once a stable network topology has been established, all bridges listen for hello bpdus bridge protocol data units transmitted from the root bridge.
In a spanning tree implementation, your network topology has a tree structure. Root path cost known in the mstp specification as the cist root. Multispanning tree protocol allows for resource conservation by now requring an instance for every single vlan in the layer 2 network. The spanning tree protocol addresses this issue in a network with physical loops by setting some redundant paths to a blocked state and leaving others in a forwarding state. Then, we will see how the spanning tree protocol creates a loopfree logical topology in a network with physical loops, so that a broadcast storm cannot occur. Multiple spanning tree multiple spanning tree protocol mstp network organized in regions regions have their own multiple spanning tree instances spanningtree topologies vlans are associated to mstis one common spanning tree cst for the entire network mstp based on rstp rapid stp. It allows a device to interact with other stpcompliant devices in your network to ensure that only one route exists between any two stations on the network.
Stpaware devices exchange bridge protocol data units bpdus periodically. Spanningtree protocol, or stp, prevents switching loops in the layer 2 portion of our network. Multiple spanning tree mst is an ieee standard inspired from the cisco proprietary multiple instances spanning tree protocol mistp implementation. Configuring multiple spanning tree protocol mstp free. These sections describe the arista spanning tree protocol implementation.
Stp is on by default, but it only really comes alive when we have two or more switches interconnected with each other. However, the network still benefits from the added reliability of redundant paths. Dec 09, 2017 spanning tree protocol stp determines the least cost path from the root bridge to other nodes in the networks. 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. Spanning tree protocol stp spanning tree protocol stp was developed to prevent the broadcast storms caused by switching loops. The spanning tree protocol stp is known to have stability problems and poor convergence intervals. Several protocols and variants exist targeting the replacement of stp variants, most of them proprietary and with limited scope of operation. Deactivate the spanning tree protocol for the ports connected to the. Port designations although bridges do not need mac addresses to operate, a mac address is needed to identify bridges in the spanning tree protocol. Rapid spanningtree is not a revolution of the original spanningtree but an evolution. Vlan trunking protocol vtp propagation of the mst configuration is not supported.
A key protocol used to maintain efficiency within a lan is the spanning tree protocol stp, which is standardized as ieee 802. I am new to networking so this probably a naive question. Rfc 7727 spanning tree protocol stp application of the. Spanning tree protocol overview presented by arash foroughi iran, november 2015 2. Read how do all the operations happen and what are the chief components of the same. Spanning tree protocol stp is a layer 2 network protocol used to prevent looping within a network topology. The very nature of ethernet is what causes the issue. Imagine that a switch has a cable loopedto itself from. The basic function of stp is to prevent bridge loops and the broadcast radiation that results from them. Just like every coin has two sides, a redundant link, along with several advantages, has some disadvantages. When too many computers try to send at the same time, overall network performance is affected and can bring all traffic to a near. 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. The multiple spanning tree protocol mstp and algorithm, provides both simple and full.
Perlman devised a method by which bridges can obtain layer 2 routing utopia. Spanning tree protocol the spanning tree protocol stp is an osi layer 2 protocol that is required to create a loop free network topology. This lab will discuss and demonstrate the configuration and verification of 802. This first major section of the chapter begins by explaining the need for stp and the basic ideas of. Modern switches use a spanning tree to determine routes through the switched network and to close off routes that could potentially cause a loop. Merge the contents of the file into your routing platform configuration by issuing. Complex protocol that is generally poorly understood.
This document assumes that the reader is familiar with rapid stp rstp 802. Besides a mac address for each bridge, each port on each bridge must be identified. 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. Multiple spanning tree multiple spanning tree protocol mstp network organized in regions regions have their own multiple spanning tree instances spanningtree topologies vlans are associated to mstis one common spanning tree cst for the entire network. Spanning treeenabled switches go through a root election process based on bridge p rotocol data unit. Before we talk about spanning tree protocol, lets organize the different variants of stp. Today we are going to cover an example of a spanning tree protocol scenario type question that you might see on your. Media in category spanning tree protocol the following 21 files are in this category, out of 21 total.
A root bridge switch is located at the bottom of the tree. Newest spanningtree questions network engineering stack. In this document, provider edge pe devices in a redundancy group rg running iccp are used to offer multihomed connectivity to spanning tree protocol stp networks to improve availability of the stp networks. Hi michael, ist0 is called ist internal spanningtree and these are the vlans that havent been mapped to another instance. In general, a graph may have several spanning trees, but a graph that is not connected will not contain a spanning tree but see spanning forests below.
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. A switching loop occurs when a cable is connectedfrom one switch port to anotherjoining a single layer two network. For two or more switches to be in the same multiple spanning tree mst. Understanding spanning tree protocol this section describes how spanning tree features work.
Spanning tree protocol forconceptualinformationaboutspanningtreeprotocol,seetheusingthespanningtreeprotocolwith theetherswitchnetworkmodule. Ive been reading up on the spanning tree protocol and understand why its necessary in a network it prevents loops and i understand that. Stp spanning tree protocol explained with examples. This is spanning tree standard called rapid spanning tree protocol. The spanning tree protocol stp is a network protocol that builds a loopfree logical topology. The device allows you to set up multiple rings with different redundancy. Exam list exam tutorial exam registration information exam policies. Spanning tree protocol runs on switches and bridges on a lan. This table shows the support for mst in various catalyst switches. Bridgingtransmitting nonip traffic or merging two networks. The election decides which switch will become the root bridge, as well as the.
However, the details of how stp does its work can take a fair amount of study and practice. With its mechanism of having redundant links, it also helps avoiding the chances of mac address instability. 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. Spanning tree protocol in layer 2layer 3 environments. Procurve secure router automatically run rapid spanning tree protocol.