When too many computers try to send at the same time, overall network performance is affected and can bring all traffic to a near. Spanning tree protocol stp is a layer 2 network protocol used to prevent looping within a network topology. The addition or removal of vlans when stp runs in pervlan spanning tree. Multiple spanning tree mst is an ieee standard inspired from the cisco proprietary multiple instances spanning tree protocol mistp implementation. First, it prevents problems caused by loops on a network. This document presents a list of recommendations that help to implement a safe network with regard to bridging for cisco catalyst switches that run catalyst os catos and cisco ios software. Spanningtree is a protocol that runs on our switches that helps us to solve loops. Not only does spanningtree blocks redundant paths but also reopens them in case of a link failure. User already knows cisco ios format and wants translation to mstpd spanningtree daemon for linux. Spanning tree protocol stp is a layer 2 protocol that runs on bridges and switches. Cisco has some extensions to improve this, for example, portfast, uplinkfast and backbonefast. When a switch receives a bridge protocol data unit bpdu in its port, it increments the path cost with the cost of the incoming port. Rapid spanningtree is not a revolution of the original spanningtree but an evolution. The original stp was developed by radia perlman while working for dce back in 1990.
Cisco spanning tree protocol guide stp examples and. Bridges will perform the spanning tree algorithm when they are first connected to the network or whenever there is a topology change. When two ports on a switch are part of a loop, the spanning tree port priority and port path cost setting determine which port is put in the. The default bridge priority of a cisco switch is 32768. Stp helps find redundant links and place one in a b. So weve seen a few now in the cisco curriculum, 802. Switches running stp will build a map or topology of the entire switching network. Cisco switches provide numerous commands that can be used to tweak specific spanningtree timers as introduced in chapter 1, and discussed in more depth in this section. By default, cisco catalyst 3550 switches used to build this scenario have spanning tree enabled in pvst mode. By means of bridge protocol data units bpdus that exchange between bridges, the stp elects the ports that eventually forward or. Infrastructure devices such as wireless bridges and switches send and receive spanningtree frames, called bridge protocol data units bpdus, at regular intervals.
This command shows only the interfaces that are active on the cisco switch. The main purpose of stp is to ensure that you do not create loops when you have redundant paths in your network. Spanning tree protocol stp determines the least cost path from the root bridge to other nodes in the networks. A cisco proprietary protocol that runs a seperate spanning tree for each vlan. This document assumes that the reader is familiar with rapid stp rstp 802. I need basic and simple explanation for 1 root bridge 2 non root bridge 3 root port 4 designated port 5 blocking port 6 there is three switches with same mac address 0001.
Cisco ccna spanning tree protocolroot bridge, root. Spanningtree operation is transparent to end stations, which cannot detect whether they are connected to a single lan segment or to a. When it comes to ethernet networks, only one active path can exist between two stations in order for them to function properly. A number of cisco ios command parameters are associated with the show spanningtree command. All switches from cisco ship with spanning tree protocol stp enabled by default, but if stp is misconfigured for any reason, you can easily enable it.
Spanning tree protocol explained step by step youtube. Spanning tree protocol stp is standardized as ieee 802. Spanning tree protocol problems and related design. To keep up with the speed of these routing protocols another flavor of spanningtree was createdrapid spanningtree. This is a configurable value between 0 to 61440 but the value has to be in increments of 4096. Before we talk about spanning tree protocol, lets organize the different variants of stp. Rapid for being a fast version of spanningtree protocol and it was labeled as 802. Spanning tree protocol was designed to avoid loops by finding redundant links in a network and shutting them down. These sections describe the arista spanning tree protocol implementation. Pvst stands for pervlan spanning tree protocol and this mode runs an instance of ieee 802. Spanning tree protacol cisco example editable cisco. Spanning tree path cost value and how is spanning tree.
And so, dont be too confused when we say root switch or root bridge, they are the same, they are the same. Many people struggle with stp so in this video, we try to break it down as much as possible. 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. Using the spanning tree protocol with the etherswitch network module. Mst was developed to reduce the number of spanning tree instances to reasonable value thus reducing cpu cycles needed to. This document discusses some of the common reasons that spanning tree protocol stp can fail and the information for which to look to identify the source of the problem. Spanning tree protocol automatically removes layer 2 switching loops by shutting down the redundant links. In a layer 2 environment with no routing, active redundant paths are neither allowed nor desirable, because that can cause loops. The devices do not forward these frames but use them to construct a loopfree path. This protocol was created by radia perlman for bridges, ethernet transparent bridges. It is quite useful and should be enabled on the switch interfaces. Spanning tree protocol stp spanning tree protocol stp was developed to prevent the broadcast storms caused by switching loops. In the below example we will configure sw2 to use fa024 as the root port for all vlans. Spanning tree protocol stp is a big topic on the ccna exam.
Spanning tree protocol stp is a link management protocol that provides path redundancy while preventing undesirable loops in the network. So the same nomenclature for the different reference points lives to this day. To prevent bridging loops redundant paths must be identified and blocked. 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.
Spanning tree protocol routeros is capable of running bridge interfaces with rmstp support in order to create a loopfree and layer2 redundant environment. Rapid spanning tree protocol rstp is the second stp type. Understanding and configuring spanning tree protocol stp. Bottom line here is that a thorough understanding of spanningtree and its benefits is a. Cisco didnt change the spanning tree protocol, but they extended it so that each vlan can have a separate spanning tree instance pvst. Spanningtree protocol types online cisco training materials.
A redundant link is usually created for backup purposes. Spanning tree protocol spanning tree protocols prevent bridging loops in layer 2 ethernet networks. For example, if the idlefree interfaces are closed by the system administrator, you will be able to view only the active interfaces with this command. Stp spanning tree protocol automatically removes layer 2 switching loops by shutting down the redundant links. Cisco 3200 series wireless mic software configuration guide. 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. What spanning tree ieee protocol does the cisco 1252ag aironet access point support.
The etherswitch network module uses spanning tree protocol stp the ieee 802. Path costs are incremented when a bridge protocol data. Understanding and configuring spanning tree protocol stp on. Cisco has also made available features such as backbonefast and uplinkfast to help converge the layer 2. Spanning tree also allows a network design to include backup links providing fault tolerance if an active link fails.
A redundant link is an additional link between two switches. As shown in example 310, the show spanningtree active command displays spanningtree configuration details for the active interfaces only. Unfortunately it only works with ciscos own vlan encapsulation method, isl. One of the most confusing things to understand when learning about the switched part of network is the spanning tree protocol stp 802. The following table lists some of the differences among the.
To enable spanning tree, connect to your switch and type spanningtree mode while in global configuration mode. Spanningtree protocol stp prevents loops from being formed when switches or bridges are interconnected via multiple paths. Lan switching configuration guide spanning tree protocol cisco. Stp is a layer 2 link management protocol that provides path redundancy while preventing loops in the network. 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. Spanning tree path cost value can be defined as the accumulated port costs from a switch other than the root bridge switch to reach the root switch. This command modifies the interface cost used in calculating the root port for spanningtree on a switch. Routing protocols like ospf and eigrp are much faster than spanningtree when they have to deal with changes in the network. Spanningtree protocol is a link management protocol that provides path redundancy while preventing undesirable loops in the network. Because a switch only segments collision domains it does not segment broadcast domains. When a bridge hears a configuration message, a special type of bpdu bridge protocol data unit, it will begin its disruptive spanning tree algorithm. 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. To provide redundant links, multiple connections are done between switches. For an ethernet network to function properly, only one active path can exist between two devices.
Please refer to the spanning tree protocol documentation for more information you can find the cisco configuration guide used to interpret their commands here spanning tree translation table. Spanning tree protocol and rapid spanning tree protocol cisco diagram example template you can edit this template and create your own diagram. And of course without spanning tree we cant have redundant pathways across our lan, and without spanningtree we cant utilise those redundant paths with etherchannel. By default, a single instance of stp runs on each configured vlan provided that you do not manually disable stp. Portfast on switch ports connected to a single workstation or server allows those devices to connect to the network immediately, instead of waiting for the port to transition from the listening and learning. Creately diagrams can be exported and added to word, ppt powerpoint, excel, visio or any other document.
The basic function of stp is to prevent bridge loops and the broadcast radiation that results from them. It is a fast converged version of spanning tree protocol as its name implies. Sometime later cisco revised the protocol with support for the ieee standard for vlan encapsulation 802. Stp spanning tree protocol explained with examples. Portfast feature causes a switch port to enter the spanning tree forwarding state immediately, bypassing the listening and learning states. Vrrp is configured on the hp 8200zl switches in the core. Arista switches support rapid spanning tree, multiple spanning tree, and rapidper vlan spanning tree protocols. In layer 2 domain, redundancy is an important case. Rstp excellent summary of rapid spanning tree protocol. Digital equipment corporation created a protocol called spanning tree protocol stp. For a layer 2 network to function properly, only one active path can exist between any two stations. To select which spanning tree protocol stp protocol to run, use the spanning tree mode command in switch configuration mode. Spanningtree protocol enhancements using loop guard and bpdu skew detection features. For an ethernet network to function properly, only one active.
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. At this time there were no switches yet, only bridges, but because bridges and switches technically. When ports are parts of a spanning tree, they go through some states before they begin to forward user traffic. Rstp bypass the blocking state and listenning state of stp, and provide forwarding state in 15 seconds. The spanning tree protocol stp is a network protocol that builds a loopfree logical topology for ethernet networks. Just like every coin has two sides, a redundant link. Multiple active paths among end stations cause loops in the network.