CISCO RSTP TUTORIAL PDF - STP is the short form for Spanning Tree Protocol & RSTP (Rapid Spanning Tree Protocol), MSTP (Multiple Spanning Tree Protocol) are all. STP is a link management protocol designed to support redundant links that stops switching loops in the STP network. Instance Vlans mapped The MST bridge either expects to receive one or to send one, depending on whether the bridge is the root of the CST or not. Now that the basic idea is understood, let’s think how it could be implemented. Cisco developed a mechanism to address the problem shown in this diagram. Note: You may want to read a newer blog post on MSTP here Understanding MSTP. From a technical standpoint, MST is the best solution. SMTP Fundamentals SMTP is an application layer protocol. This document assumes that the reader is familiar with Rapid STP (RSTP) (802.1w), as MST heavily relies on this other IEEE standard. Most of the internet systems use SMTP as a method to transfer mail from one user to another. See the wiki page: Also MSTPD includes a number of useful features which are not defined in802.1Q-2005 standard, but are found on many commercial switches. Please call 1-877-224-8987 (Outside US: 1-775-826-4344) or fill out the form below to have a training advisor contact you. interface FastEthernet0/13 Carefully decide how many instances are needed in the switched network, and keep in mind that an instance translates to a logical topology. Now that we have basic understanding of how MSTP works inside a region, let’s jump to the configuration stage. Change the STP type to MST, and work your way down to the access switches. This implies that the IST (instance 0) is always present everywhere inside an MST region. Here we’ve selected the Bacnet MSTP protocol at tab11, picked the ‘destination address’ filter at tab 12, selected ‘==’ at tab 13 to pick an exact match and finally entered the Bacnet address ID in hex format, 0x03 at tab 14. 2 Altn BLK 200000 128.18 40,50,60. However, until recently, redundant switched networks had to rely on the relatively sluggish 802.1d STP to achieve those goals. Each switch running MST in the network has a single MST configuration that consists of these three attributes: An alphanumeric configuration name (32 bytes), A configuration revision number (two bytes), A 4096-element table that associates each of the potential 4096 VLANs supported on the chassis to a given instance. BACnet MSTP is a token passing protocol. There is no need to run 1000 instances. MSTI1 and MSTI2 in this case for VLAN2/VLAN3) and avoid mapping VLANs to IST. Cisco also provides an efficient yet simple compatibility mechanism between MST and PVST+. switchport mode trunk, SW3: When Switch A and Switch B exchange STP information for VLAN 20, the switches send an IST BPDU with an MRecord for instance 1 because that is where VLAN 20 is mapped. Operational hello time 2 , forward delay 15, max age 20, txholdcount 6 Fa0/16 Altn BLK 200000 128.18 P2p, SW1#show spanning-tree mst interface fastEthernet 0/13, FastEthernet0/13 of MST0 is designated forwarding MSTP Tutorial Before we start with MSTP (Multiple Spanning Trees Protocol), I would like to note that this tutorial is going to be is divided in two parts. Through these forms of promotion, MSTP technology has a wide range of bandwidth and bandwidth adaptation capabilities, while supporting more functions, including ATM services, and effective … For two switches to become members of the same region, the following attributes must match: IEEE 802.1s implementation does not send a BDPU for each active STP instance, nor does it encapsulate VLAN list in each configuration message. The CPU is spared; only one instance needs to be computed. Shortly after this is completed, the network administrator notices that users in VLAN 20 have lost connectivity to the network. However, this solution has proven to be too complex and potentially dangerous when first implemented in the MISTP. Instead of this, IST BDPUs has special field called MaxHops. Bridge address 0019.5684.3700 priority 32768 (32768 sysid 0) * The Port ID: The transmitting switch port ID, will be discussed later.. 2. The idea is that several VLANs can be mapped to a reduced number of spanning tree instances because most networks do not need more than a few logical topologies. Our staff is looking forward to assisting you! To avoid such situations, use separate STP for each logical topology (e.g. With the implementation of these new protocols, convergence times in the low hundreds of milliseconds can be expected while scaling to thousands of VLANs. The IST can represent the entire MST region as a CST virtual bridge to the outside world. As for IST (MSTI0), let’s make SW3 the root switch for it (though it’s not recommended to assign root roles to access switches). ! In this diagram, Bridge A in the MST region is the root for all three PVST+ instances except one (the red VLAN). Unfortunately, this is the only port that VLAN3 can use. In the PVST+ implementation, the association is as follows: Different VLANs carry the BPDUs for their respective instance (one BPDU per VLAN). VLANs 10 and 20 are both mapped to instance 1, which means there is only one logical topology for both VLANs. Decide what VLANs to map onto those instances, and carefully select a root and a back-up root for each instance. STP is the short form for Spanning Tree Protocol & RSTP (Rapid Spanning Tree Protocol), MSTP (Multiple Spanning Tree Protocol) are all advanced/ improved implementations of STP. Seeing the limitations of PVST approach, Cisco came with idea of decoupling the STP instance from a VLAN (they were bound together in PVST). Bpdus sent 550, received 1099, Instance Role Sts Cost Prio.Nbr Vlans mapped This diagram shows the logical topology of the IST instance: Switch B receives two BPDUs for instance 0 from Switch A (one on each port). 0 Root FWD 200000 128.18 1-9,11-19,21-29,31-39,41-49,51-59 interface FastEthernet0/16 This table shows the support for MST in various Catalyst switches: For more information on RSTP (802.1w), refer to this document: Understanding Rapid Spanning Tree Protocol (802.1w). Before we continue discussing IEEE’s implementation, let’s define MSTP region as a collection of switches, sharing the same view of physical topology partitioning into set of logical topologies. If by error, two switches were misconfigured and had a different range of VLANs associated to the same instance, it was difficult for the protocol to recover properly from this situation. This means that all PVST+ instances have a better root than the IST instance, as shown in this diagram: This case corresponds to a PVST+ core and an MST access or distribution layer, a rather infrequent scenario. The exact same mechanism also leads Bridge A to block its boundary port. This standard defines a Common Spanning Tree (CST) that only assumes one spanning tree instance for the entire bridged network, regardless of the number of VLANs. The port is placed in the root inconsistent mode. In this diagram, the port on B1 is at the boundary of region A, whereas the ports on B2 and B3 are internal to region B: According to the IEEE 802.1s specification, an MST bridge must be able to handle at least these two instances: One or more Multiple Spanning Tree Instance(s) (MSTIs). Namely: 1. In generic terms, a port is at the boundary of a region if the designated bridge on its segment is in a different region or if it receives legacy 802.1d BPDUs. Remember that VLAN no longer means spanning tree instance. In order to easily achieved this, elect Bridge D1 to be the root for VLANs 501 through 1000, and Bridge D2 to be the root for VLANs 1 through 500. Figure 2: The MSTP contains IST (VLAN1,10) and a MSTI (VLAN20). All logos, trademarks and registered trademarks are the property of their respective owners. Consider the following physical topology already mentioned above: The topology has VLANs 1, 10,20,30,40,50,60. The diagram shown here demonstrates MST BDPUs sent inside and outside of an MST region: The MRecord contains enough information (mostly root bridge and sender bridge priority parameters) for the corresponding instance to calculate its final topology. A key design criterion (enumerated in some detail at the kick-off meeting in Nashville) was that the protocol had to be applicable to all building automation needs. The IEEE 802.1s committee adopted a much easier and simpler approach that introduced MST regions. Different paths … In this setup, users connect to Switch A, and the network administrator typically seeks to achieve load balancing on the access switch Uplinks based on even or odd VLANs, or any other scheme deemed appropriate. The first part describes how MSTP works inside a single region (the definition of the term will follow later). Cisco released PVST+ at the same time as support for 802.1q was announced. Once a switch receives a BPDU, the switch extracts the digest (a numerical value derived from the VLAN-to-instance mapping table through a mathematical function) and compares this digest with its own computed digest. The details pane, found in the middle, presents the protocols and protocol fields of the selected packet in a collapsible format. The show command reveals that Switch B is blocking the link to Switch A in VLAN 10, as shown in the this diagram: How is that possible in such a simple topology, with no apparent loop? Instead of that, a special STP instance number 0 called Internal Spanning Tree (IST or MSTI0) is designated to carry all “signaling” information. If you decide to remove some VLANs off a trunk, remove all the VLANs mapped to a given instance together. However, because it is an IST BPDU, this BPDU also contains information for instance 0. Added by Satish Ashok. A failed simulation puts the boundary port in root inconsistent mode. port Fa0/13 cost 200000 rem hops 19, Interface Role Sts Cost Prio.Nbr Type This is the term often generically applied to anything Internet or anything using "standard" networking. Share data among different vendor's systems for a more sensible and integrated approach to facilities management Access all systems from a common interface to permit common graphics, event and alarm enunciation, and data logging The MSTIs information is piggybacked into IST BPDUs in special MRecord fields (one for every active MSTI), which carries root priority, designated bridge priority, port priority and root path cost among others. One spanning tree instance for each VLAN is maintained, which means 1000 instances for only two different final logical topologies. Consider the following example: In this topology, VLANs are manually pruned on trunks. The IEEE recently decided to incorporate most of these concepts into two standards: 802.1w (RSTP) and 802.1s (MST). Switched networks must fulfill stringent robustness, resiliency, and high-availability requirements. These statements are true for this configuration: In this case, optimum load balancing results. Fa0/13 Root FWD 200000 128.15 P2p The first part of this tutorial is the following. Please advise if the MSTP configuration for priority is right as per Figure 2. The IST Instance is Active on All Ports, Whether Trunk or Access section illustrates some common pitfalls and how to avoid them. Bridge address 0019.5684.3700 priority 32770 (32768 sysid 2) This is accomplished by running multiple spanning trees in a topology and mapping VLANs to different trees for traffic forwarding. For more information refer to the Region Boundary section of this document. Since the filtering is not consistent with the respective MSTI blocking decisions, VLAN2 traffic is blocked between SW1 and SW2. Let’s review the effect of our configuration. The full form of STP is Spanning Tree Protocol. Root address 001e.bdaa.ba80 priority 8194 (8192 sysid 2) Cisco remains the leader in the industry and offers these two protocols along with proprietary augmentations in order to facilitate the migration of and interoperability with legacy bridges. BPDUs for the green instance are not sent out of the MST region. Multiple Spanning Tree (MST) is an IEEE standard inspired from the Cisco proprietary Multiple Instances Spanning Tree Protocol (MISTP) implementation. Link type: point-to-point (auto) bpdu filter: disable (default) spanning-tree mst 2 priority 8192 More precisely, how to tag BPDUs so that the receiving devices can identify the instances and the VLANs to which each device applies. Well, obviously, all VLANs could be mapped to IST – this is the default configuration. interface FastEthernet0/16 Edge port: no (default) port guard : none (default) The communication protocol consists of a set of rules that monitors data that is exchanged between devices, enabling communication among devices in a network. However, with the number of VLANs growing, PVST becomes a waste of switch resources and management burden, for the number of logical topologies is usually much smaller than the number of active VLANs. Here the MS stands for Master - Slave and the TP stands for Token Passing.This flavor of BACnet is mainly used for connecting field devices to controllers / routers / control applications. BACnet was designed specifically to meet the communication needs of building automation and control systems. VLAN 10 is mapped to instance 0, while VLAN 20 is mapped to instance 1. The UDP side of the stack operates in parallel to TCP, and is automatically included in most implementations of an Ethernet based protocol stack. The terminology continues to evolve, as 802.1s is actually in a pre-standard phase. Petr works with all of the technologies covered within his four CCIE tracks on a daily basis, staying current with any changes in the industry. multiple root bridges? The CPU is spared because only two instances are computed. Have questions? 1 10,20,30 Notice the location of the different blocked ports. The preferred solution is to use one instance for VLAN 10 and another instance for VLAN 20 to avoid mapping VLANs to the IST instance. Switch3 is the root for MSTI. ---------------- ---- --- --------- -------- -------------------------------- The initial implementation was called MISTP (Multiple Instances Spanning Tree) and later evolved into new IEEE 802.1s standard called MSTP (Multiple Spanning Trees Protocol). ! Among others fields there are configuration name, revision number and a hash value computed over VLAN to STP instance mapping table contents. port Fa0/16 path cost 0 MST seamlessly interoperates with standard 802.1q CST networks; however, only a handful of networks are based on the 802.1q standard because of its single spanning tree restriction. Effectively, this represents the case of classic IEEE RSTP with all VLANs sharing the same spanning-tree. First of all, since MSTP convergence mechanism stems from RSTP, there is no BDPU relaying process downstream from the root bridge. SW1#show spanning-tree mst, ##### MST0 vlans mapped: 1-9,11-19,21-29,31-39,41-49,51-59,61-4094 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. Switch5 is the root switch, and root for IST. As soon as hop count becomes zero, the information in BPDU is ignored, and the switch may start declaring itself as new IST root. Ensure all switch-to-switch links, on which a rapid transition is desired, are full-duplex. This issue is explained by the fact that MST information is conveyed with only one BPDU (IST BPDU), regardless of the number of internal instances. The root path cost is used to elect root port and we will discuss in the next part. Unlike the IST, MSTIs never interact with the outside of the region. This does not mean that there is a loop in VLANs 10 through 50. The cost values are much higher than the default STP costs, and MSTIx is called MSTx (e.g. Root port is the port that is closest to the root bridge, which means it is the port that receiving the lowest-cost BPDU from the root.. Every non-root bridge must have a root port. The exact mechanism that makes the region appear as one virtual CST bridge is beyond the scope of this document, but is amply described in the IEEE 802.1s specification. this link is non-backup in your logical topology), ensure the STP instance it maps to is forwarding on this link". Can we have… multiple STPs? In the topology described in the first diagram, there are only two different final logical topologies, so only two spanning tree instances are really necessary. The IST instance is simply an RSTP instance that extends the CST inside the MST region. Note that STP timers such as Hello, ForwardTime, MaxAge could only be tuned for IST, the instance 0. The Spanning Tree Protocol (STP) is a network protocol that builds a loop-free logical topology for Ethernet networks.The basic function of STP is to prevent bridge loops and the broadcast radiation that results from them. Petr Lapukhov has more than 12 years of experience working with Cisco Systems products. Load-sharing cannot be achieved, as shown here: Because of the manual pruning, VLAN 20 is only allowed on the blocked port, which explains the loss of connectivity. This diagram shows a BPDU exchange between Switches A and B inside an MST region. With growing technologies such as Voice over IP (VoIP) and Video over IP, fast convergence around link or component failures is no longer a desirable characteristic: fast convergence is a must. The BPDUs for IST contain all standard RSTP information for IST itself, as well as carry additional informational fields. We want to achieve the following: 1) VLANs 10,20,30 should follow uplink from SW3 to SW1 2) VLANs 40,50,60 should follow uplink from SW3 to SW2 3) If any of the uplinks fail, the respective VLANs should use the other uplink. The table of 4096 elements which map the respective VLAN to STP instance number. Bridge C is the root of the red VLAN. In order to achieve load balancing, the network administrator must map VLAN 10 and 20 to two different instances. In order to clearly understand the role of the IST instance, remember that MST originates from the IEEE. Thanks Edge port: no (default) port guard : none (default) To accomplish this, we need to create two MSTIs - let's give them numbers 1 and 2. The MST region replicates the IST BPDU on all the VLANs to simulate a PVST+ neighbor. For more information refer, to the Interaction Between MST Regions and the Outside World section of this document. You just need to execute some caution, when filtering and mapping VLANs, but if you plan logical topologies in advance this should not cause any problems. In this lesson, we will configure MSTP on Huawei switches with Huawei eNSP. Note: In this diagram, notice that the first information field carried by an MST BPDU contains data about the IST. Never remove an individual VLAN from a trunk and not remove all the VLANs that are mapped to the same instance. Note: If for any reason two switches differ on one or more configuration attribute, the switches are part of different regions. The second part is dedicated to MSTP region interaction with other regions and different STP protocols (IEEE STP, RSTP and Cisco PVST+). Also, that virtual bridge is on the C to D segment and leads Switch D to block its port. As for this part, you can see that configuration MSTP inside a region is pretty simple. Switches running STP will build a map or topology of the entire switching network. This considerably wastes CPU cycles for all of the switches in the network (in addition to the bandwidth used for each instance to send its own Bridge Protocol Data Units (BPDUs)). ! Obviously, due to multiple logical topologies a single port could be blocking for one instance and forwarding for another (note that in (R)PVST+ a port is either forwarding or discarding for a VLAN). instance 2 vlan 40, 50, 60 It is up to the network administrator to properly propagate the configuration throughout the region. Individual instances do not send individual BPDUs. 61-4094 ! UDP/IP - Virtually everyone has heard the term TCP/IP. However, PVST+ bridges run one Spanning Tree Algorithm (STA) per VLAN, and as a result, send one BPDU on each VLAN every two seconds. Configured hello time 2 , forward delay 15, max age 20, max hops 20, Interface Role Sts Cost Prio.Nbr Type interface FastEthernet0/13 You may contact Petr Lapukhov at [email protected] Glossary of BACnet terms. The Multiple Spanning Tree Protocol (MSTP) and algorithm, gives both straightforward and full network doled out to any given Virtual LAN (VLAN) all through a Bridged Local Area Network. This means that the IST instance is active on all ports inside an MST region, whether these ports carry VLANs mapped to the IST instance or not. If you interact with a PVST+ bridge through a trunk, ensure the MST bridge is the root for all VLANs allowed on that trunk. Using just this compact information it’s easy to detect misconfiguration on two neighboring switches. Introduction []. The following questions need to be answered: Original Cisco MISTP pre-standard implementation sends separate BPDUs for each instance – this allows for separate STP calculations. switchport mode trunk. It is clear that Switch B has to block one of its ports in order to avoid a loop. MSTIs do not send independent individual BPDUs. 61-4094 If the CST is applied to the topology of this diagram, the result resembles the diagram shown here: In a network running the CST, these statements are true: No load balancing is possible; one Uplink needs to block for all VLANs. Boundary : internal bpdu guard : disable (default) All other instances (MSTIs) inherit the timers from IST – this is the natural result of all MSTI information being piggybacked in IST BPDUs. Configuration Example to Migrate the Spanning Tree from PVST+ to MST, Spanning Tree from PVST+ to Rapid-PVST Migration Configuration Example. spanning-tree mst configuration Instead of running an STP instance for each VLAN, let’s run a number of VLAN-independent STP instances (representing logical topologies) and then map each VLAN to the most appropriate logical topology (instance). Edge ports are defined through the PortFast feature. Q: configuring MSTP with only a default IST has the same result as configuring the 3 switches with RSTP? Another possibility is to have the IST region be the root for absolutely no PVST+ instance. This diagram shows a common design that features access Switch A with 1000 VLANs redundantly connected to two distribution Switches, D1 and D2. switchport trunk encapsulation dot1q Stay connected with the latest news, product releases and promotions from INE by subscribing to our Newsletter. However, if you keep this virtual bridge property of the MST region in mind, the interaction with the outside world is much easier to understand. These instances run the RSTP automatically by default, without any extra configuration work. Fa0/16 Root FWD 200000 128.18 P2p, ##### MST1 vlans mapped: 10,20,30 The original IEEE 802.1q standard defines much more than simply trunking. Cisco also answered large Layer 2 (L2)-based networks' scalability issues with the development of the MISTP. Thus, the number of STP instances is kept to minimum (saving switch resources), but the network capacity is utilized in optimal fashion, by using all possible paths for VLAN traffic. This often turned out to be the network administrator's most challenging task. As MSTIs depend on the IST to transmit their information, MSTIs do not need those timers. ------------------------------------------------------------------------------- As previously mentioned, the main enhancement introduced by MST is that several VLANs can be mapped to a single spanning tree instance. The only instance in the MST region to use these parameters is the IST; the hello time determines how frequently BPDUs are sent, and the forward delay parameter is mainly used when rapid transition is not possible (remember that rapid transitions do not occur on shared links). -------- ---- --- --------- -------- ------------------------------- 1 Desg FWD 200000 128.18 10,20,30 The red links represent the IST, and therefore also represent the CST. The Cisco per-VLAN BPDUs are tunneled by pure 802.1q bridges. If the PVST+ bridge is the root, this bridge must be the root for all VLANs (including the CST, which always runs on VLAN 1, regardless of the native VLAN, when the CST runs PVST+). Enhanc… In order to be part of a common MST region, a group of switches must share the same configuration attributes. The switch forwarding logic for VLAN traffic was changed a little bit. This is a typical misconfiguration problem. Each switch only sends one BPDU, but each includes one MRecord per MSTI present on the ports. Rapid Spanning Tree Protocol (RSTP) One big disadvantage of STP is the low convergence which is very important in switched network. Interaction with legacy bridges can be a challenge. Added by Satish Ashok. Fa0/16 Desg FWD 200000 128.18 P2p, ##### MST2 vlans mapped: 40,50,60 1 Desg FWD 200000 128.15 10,20,30 spanning-tree mst configuration This means that Bridge B is designated for all VLANs except the red one. In other terms, there is no load balancing possible between the region's two Uplinks that lead to Switch C. The Uplink on Switch B for the instance will be blocking for all VLANs while Switch A will be forwarding for all VLANs. STP was originally defined in IEEE 802.1D.

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