And so, dont be too confused when we say root switch or root bridge, they are the same, they are the same. This creates a loopfree logical topology, so that a broadcast storm cannot occur. Example of a bridged network with a loop, and the minimum spanning tree with the loop removed. On each switch, display the spanning tree table with the show spanning tree command.
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. Understanding spanning tree protocols stp, rstp, mstp. The main purpose of stp is to ensure that you do not create. Edc0 this bridge is the root hello time 2 sec max age 20 sec forward delay 15 sec bridge id priority 32769 priority 32768 sysidext 1 address 0001. How to manage rapid spanning tree rstp thru command line.
Root selection varies depending on the bid of each switch in your lab. A wellknown spanning tree algorithm is the breadth first search algorithm. Apr 16, 2011 so, rapid spanning tree protocol rstp was conceived to overcome this problem rstp takes 56 seconds to update and reconfigure the new network topology routes. Spanningtree is used on switches to create a loopfree l2 topology. Spanning tree protocol example rstp protocol in networking. The spanning tree protocol is primarily known today by its three most popular variants. Pdf formal specification of spanning tree protocol using acp. In practical scenario, redundant links are created to avoid complete network failure in. In the graph, all potential neighbors are connected. The mac address comes from the bridge vendor, but the priority. So weve seen a few now in the cisco curriculum, 802. Just like every coin has two sides, a redundant link, along with several advantages, has some disadvantages. On each bridge, select a root port port with the least cost path to the root bridge. 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.
In simple words, whenever a topology change occurs in the network e. Read how do all the operations happen and what are the chief components of the same. In spanning tree protocol configuration, the shortest path to the root bridge switch is called the root port. Spanningtree protocol is a link management protocol that provides path redundancy while preventing undesirable loops in the network. Spanning treeinstanceinterfaceshavepriorities36 whatisspanningtreeinstanceinterfacecost. Aug 29, 2017 spanning tree protocol stp is a big topic on the ccna exam. Stp will identify if there are any loops, and then disable or block.
Root bridge is a switch in a single vlan or whole topology according to the type of stp standard used which is responsible for distributing bpdus and block the least redundant port. Im implementing hsrp on core switch in my network, but spanning tree always block one port on the layer 2 switch. Spanning tree protocol routeros is capable of running bridge interfaces with rmstp support in order to create a loopfree and layer2 redundant environment. The following code will enable the cisco proprietary rapid per vlan spanning tree protocol pvst over the open standard of multiple spanning tree protocol mstp. Understanding and configuring spanning tree protocol stp on. Stp spanning tree protocol step by step configuration. This protocol also allows a network design to include redundant links for providing automatic backup paths. Spanning tree protocol concepts and configuration spanning. Spanning tree protocol stp has nowadays been implemented by most manufacturers in order to avoid loops in bridged networks. Spanning treeenabled switches go through a root election process based on bridge p rotocol data unit. First, it prevents problems caused by loops on a network. Besides a mac address for each bridge, each port on each bridge must be identified.
Stp spanning tree protocol automatically removes layer 2 switching loops by shutting down the redundant links. This protocol was created by radia perlman for bridges, ethernet transparent bridges. The spanning tree algorithm itself is defined by the ieee standard 802. Understanding and configuring spanning tree protocol stp. The basic function of stp is to prevent bridge loops and ensuing broadcast radiation. Spt is employed for the prevention of bridge loops and the broad cast radiation of them. Abcs of spanning tree protocol contemporary controls.
For bridges, a unique 64bit bridge identifier is assigned by appending a 16bit priority field in front of a unique 48bit mac address resulting in a bridge id. Spanningtree protocol stp has nowadays been implemented by most manufacturers in order to avoid loops in bridged networks. Understanding and configuring spanning tree protocol stp on catalyst switches contents introduction prerequisites requirements components used background theory network diagram concepts description of the technology stp operation task stepbystep instructions verify troubleshoot stp path cost automatically changes when a port speedduplex is. However, the network still benefits from the added reliability of redundant paths. Understanding spanning tree protocol this section describes how spanning tree features work.
The stp uses the spanning tree algorithm sta algorithm to avoid loops. A redundant link is usually created for backup purposes. What is rapid spanning tree protocol sysnettech solutions. Stop, when n 1 edges have been added, because then we must have spanning tree. The problem is that when we create redundancyat a layer 2 level of our networks,we create loops that traffic will traverse indefinitely. Stp is enabled by default on all vlans on catalyst switches. Therefore, the switch2 and switch3 ethernet0 0 interfaces above will be configured as root ports. Lecture notes on spanning trees carnegie mellon school. Spanning tree is basically used to find a minimum path to connect all nodes in a graph. Configuring stp protocol techlibrary juniper networks. We start with the graph where the vertices are the cells and the edges represent the neighbors we can move to in the maze. In the link or the cable failure that occurs on the network configured the spanning tree protocol, it is calculated the. Understanding stp, understanding system identifiers for bridges in stp or rstp instances, configuring stp on ex series switches cli procedure. Once the root switch is elected, each of the ports is given a role depending on its place within the stp topology.
So the same nomenclature for the different reference points lives to this day. Dec 09, 2017 spanning tree protocol stp determines the least cost path from the root bridge to other nodes in the networks. Switches running stp will build a map or topology of the entire switching network. Download spanning tree protocol interview questions and. The spanning tree protocol stp is a network protocol that ensures a loopfree topology for any bridged ethernet local area network. How to manage rapid spanning tree rstp thru command line on. Root selection varies depending on the bid of each switch in your lab resulting in varying outputs. Although the operational logic of the stp is mainly mixed, it is very easy to configure on switches. If you have not yet registered, you will be prompted to register, before proceeding to access this content. Stp spanning tree protocol chooses the best path as well as preventing loops on the network. This content is only accessible by registered users. Spanning tree protocol this document descibes spanning tree protocol stp in a wireless environment.
Second, when redundant loops are planned on a network, stp deals with remediation of network. Stp spanning tree protocol explained with examples. For an ethernet network to function properly, only one active. Spanning tree root port is used to select path cost. Spanning tree protocol spanning tree overview 1459 multiple spanning tree instances mstis consist of vlans that are assigned through mst configuration statements.
Traditional spanning tree protocol, by implementation, takes about fifty 50 seconds to adapt and converge to topology changes. Vlan0005 spanning tree enabled protocol ieee root id priority 32773 address 00. 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. The spanning tree protocol stp is a network protocol that builds a loopfree logical topology for ethernet networks. Sorting the edges will take oe loge steps with most appropriate sorting algorithms. The basic function of stp is to prevent bridge loops and the broadcast radiation that results from them. Spanningtree protocol is a protocol used in switching network to create a loopfree topology. Perlman devised a method by which bridges can obtain layer 2 routing utopia. The spanning tree protocol run my experiment on geni. A root port carries traffic back to the root bridge with the. Vlans assigned to an msti are removed from the ist instance. Vlans in an msti operate as a part of a single spanning tree topology. 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.
Many people struggle with stp so in this video, we try to break it down as much as possible. Spanning tree protocol stp spanning tree protocol stp was developed to prevent the broadcast storms caused by switching loops. Spanning tree protocol stp determines the least cost path from the root bridge to other nodes in the networks. 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. In this article, we will try to understand the basic concepts of spanning tree protocols and their implementation. A designated port is a port that forwards traffic away from the root and toward the leaves. Spanning tree also allows a network design to include spare redundant links to provide automatic backup paths if an active link fails. 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. Stp path cost automatically changes when a port speedduplex is changed troubleshoot commands command summary related information introduction spanning tree protocol stp is a layer 2 protocol that runs on bridges and switches. Spanning tree protocol stp is a protocol which prevents layer 2 loops. The node with the smallest id is selected the root bridge 2. In rstp, link status of each port are monitored proactively instead of waiting for the bpdu messages to detect network topology changes.
This article explains how rapid spanning tree protocol rstp is implemented on dell networking powerconnect switches thru command line interface cli. Stp overview stp is a layer 2 link management protocol that prov ides path redundancy while preventing loops in the network. Spanning tree protocol spanning tree overview 1461 the following sections describe spanning tree configuration parameters. Stp enables switches to become aware of each other so that they can negotiate a loopfree path through network. Spanning tree protocol in layer 2layer 3 environments. Stp switches send bpdus bridge protocol data units to each other to form their topology databases. Understanding spanning tree protocol this section describes how spanningtree features work. Why does this create a minimumweight spanning tree. To create a loopfree tree, bridges in the network exchange bpdus, and execute the spanning tree protocol as follows. Download what is spanning tree protocol stp and its types in pdf click here 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.
Under normal conditions, the path costs assumed by the ieee are calculated as. This is because layer 2 ethernet frameshave no time to live or time out mechanismbuilt into the frame. It is a straightforward application of the cycle property see exercise2. A redundant link is an additional link between two switches. In these lessons you will learn the basics of spanningtree and the different versions. It is always recommended to manually set up each bridges priority, port priority, and port path cost to ensure proper layer2 functionality at all times. Radia perlman, distinguished engineer at sun microsystems. The idea of this algorithm is to start with a node as a root of the tree, and then sweep through all its neighbors first to select to add to the tree as the first hop away from the root node. Spanning tree also allows a network design to include backup links providing fault tolerance if an active link fails. Rootthe port given this role is the selected best path to reach the root switch. Spanning tree protocol spt is a network protocol which make sure of loopfree topology for any bridged ethernet local area network.
Rapid for being a fast version of spanningtree protocol and it was labeled as 802. Rapid spanning tree protocol rstprstp is defined in ieee 802. Consider, city network as a huge graph and now plans to deploy telephone lines in such a. Spanning tree protocol stp is used to make a loop free network by monitoring the network to track all the links and shut down the least redundant ones. In addition to configuring stp on the switch, you will also configure port 2 on the switch for portfast, which allows the port to immediately transition to forwarding mode. You will learn how spanningtree works and how you can verify the spanningtree config on cisco switches. What is spanning tree protocol stp sysnettech solutions. Spanning tree protocol explained step by step youtube. 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.
323 821 93 417 675 385 315 1274 659 1254 611 1156 641 1315 93 228 166 469 805 244 1200 352 993 41 9 1093 132 960 338 180 592 137 535 1303 272 1136 897