internal cost 200000 rem hops 19 Root address 0012.d939.3700 priority 8192 (8192 sysid 0) As time passed, STP evolved into RSTP and Cisco answered with Rapid-PVST+: the fast STP, but with the same per-VLAN instance concept. 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. UDP/IP - Virtually everyone has heard the term TCP/IP. He has also received his Cisco Certified Design Expert (CCDE) certification, joining a small group of distinguished individuals who have achieved this status. 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. The details pane, found in the middle, presents the protocols and protocol fields of the selected packet in a collapsible format. BACnet protocol supports communication and control of applications such as heating, ventilation, air-conditioning, lighting, access, and fire detection systems and their associated equipment. These are two functionally equivalent diagrams. Note a few things here. Ensure all switch-to-switch links, on which a rapid transition is desired, are full-duplex. Since the filtering is not consistent with the respective MSTI blocking decisions, VLAN2 traffic is blocked between SW1 and SW2. instance 1 vlan 10, 20, 30 Multiple Spanning Tree (MST) is an IEEE standard inspired from the Cisco proprietary Multiple Instances Spanning Tree Protocol (MISTP) implementation. Instead of blocking on D, you expect to have the second loop broken by a blocked port somewhere in the middle of the MST region. MSTP was designed to overcome one major problem with classic STP protocol – inability to use blocked links for traffic forwarding due to single STP instance present. If you map half of the 1000 VLANs to a different spanning tree instance, as shown in this diagram, these statements are true: The desired load balancing scheme can still be achieved, because half of the VLANs follow one separate instance. It was developed by ASHRAE. The single spanning-tree instance used by IEEE and per-VLAN STP implemented by Cisco represents two poles in the space of possible solutions. 1 10,20,30 This diagram shows Switches A and B connected with access ports each located in different VLANs. STP port states In STP mode, each switch port can be in one of five spanning tree states, and one of two switch states.The state of a switch port is taken into account by STP.The STP port states * The Port ID: The transmitting switch port ID, will be discussed later.. 2. Remember that MST only runs one spanning tree outside of the region, so except for the IST instance, regular instances inside of the region have no outside counterpart. An alternative is to carry those VLANs mapped to the IST on all links (allow VLAN 10 on both ports, as in this diagram). Bridge address 0019.5684.3700 priority 8193 (8192 sysid 1) There is no need to run 1000 instances. 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. In the PVST+ implementation, the association is as follows: Different VLANs carry the BPDUs for their respective instance (one BPDU per VLAN). A BACnet device is often comprised of a microprocessor-based controller and software combination that is designed to understand and use the BACnet protocol. (WARNING: it might be dropped in the future and replaced by theAutoIsolate feature of 802.1Q-2011) 3. 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)). 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. Therefore, MST must be able to interact with 802.1q-based networks, because 802.1q is another IEEE standard. 0 Root FWD 200000 128.18 1-9,11-19,21-29,31-39,41-49,51-59 In this diagram, Bridge A in the MST region is the root for all three PVST+ instances except one (the red VLAN). Before we jump to configuration examples, let’s consider some issues, which may arise from the fact that spanning-tree instances now are not directly tied to VLANs. Unlike regular converged spanning tree topology, both ends of a link can send and receive BPDUs simultaneously. The IEEE recently decided to incorporate most of these concepts into two standards: 802.1w (RSTP) and 802.1s (MST). The Cisco implementation supports 16 instances: one IST (instance 0) and 15 MSTIs. STP was originally defined in IEEE 802.1D. 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. You may contact Petr Lapukhov at petr@ine.com. ! However, due to the IST, the entire region appears as one virtual bridge that runs a single spanning tree (CST). Edge port: no (default) port guard : none (default) Unlike the IST, MSTIs never interact with the outside of the region. Why a Standard Protocol? Notice the location of the different blocked ports. MSTP Configuration on Huawei eNSP. Cisco’s original proposal was as follows. SW1 will be the root for instance 1 and SW2 will be the root for instance 2. BPDUs for the green instance are not sent out of the MST region. switchport trunk encapsulation dot1q First of all, since MSTP convergence mechanism stems from RSTP, there is no BDPU relaying process downstream from the root bridge. To accomplish this, BACnet specifies most all of the most common functions: analog and binary input, output, and values; control loops; schedules, etc., that clearly apply to almost any kind of monitoring or control application. Note: As soon as a boundary port produces a root inconsistent error, investigate whether a PVST+ bridge has attempted to become the root for some VLANs. If you establish the root bridge outside the region, there are these drawbacks as compared to the previously recommended configuration: An MST region only runs one spanning tree instance that interacts with the outside world. Cisco recommends that you place as many switches as possible into a single region; it is not advantageous to segment a network into separate regions. Additionally, MSTIs do not send BPDUs outside a region, only the IST does. Suppose that the loop created on the red VLAN, where Bridge C is the root, becomes blocked by Bridge B. Each MSTI may assign different priorities to switches, may have different link costs, port priorities and thus end up with it’s own logical topology. As soon as hop count becomes zero, the information in BPDU is ignored, and the switch may start declaring itself as new IST root. 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. Select one root port per nonroot bridge. This means that Bridge B is designated for all VLANs except the red one. The IST instance is simply an RSTP instance that extends the CST inside the MST region. 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. SMTP is a push protocol and is used to send the mail whereas POP (post office protocol) or IMAP (internet message access protocol) are used to retrieve those mails at the receiver’s side. 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. 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. However, the network administrator does not have to map VLANs onto instance 0, and therefore this is not a source of concern. What about other instances, besides the IST thing? © 2019 INE Inc. All Rights Reserved – Terms of Service – Privacy Policy All logos, trademarks and registered trademarks are the property of their respective owners. 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. 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? MSTP is an enchanced STP version. To overcome this, Cisco suggested its proprietary PVST/PVST+ solution, running a separate STP instance for each VLAN. 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. This diagram shows an interoperability issue. switchport mode trunk These are the basic rules that must be followed to get a successful MST and PVST+ interaction: If the MST bridge is the root, this bridge must be the root for all VLANs. However, because it is an IST BPDU, this BPDU also contains information for instance 0. This is a typical misconfiguration problem. Each BDPU contains instance number and a list of VLANs, mapped on sending switch to this particular instance – this allows for consistency check. Namely: 1. Note: In this diagram, notice that the first information field carried by an MST BPDU contains data about the IST. It is a Layer 2 protocol that runs on bridges and switches, which should be enabled on the switch interfaces. 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). Enhanc… In this particular case, interaction between PVST+ and the MST region is optimal because: Switch C's Uplink ports' costs can be tuned to achieve load balancing of the different VLANs across the Uplinks' ports (because Switch C runs one spanning tree per VLAN, this switch is able to chose which Uplink port blocks on a per-VLAN basis). Note: If for any reason two switches differ on one or more configuration attribute, the switches are part of different regions. In order for a frame to be forwarded out of a port, two conditions must be met: first, VLAN must be active on this port (e.g. While the way the IST behaves inside the region in order to have the whole MST region resemble a CST bridge was not discussed in detail, you can imagine that a switchover across a region is never as efficient as a switchover on a single bridge. The MRecord does not need any timer-related parameters such as hello time, forward delay, and max age that are typically found in a regular IEEE 802.1d or 802.1q CST BPDU. Cisco has released many 802.1d STP augmentations such as UplinkFast, BackboneFast and PortFast, features that paved the way toward faster spanning tree convergence. Our staff is looking forward to assisting you! The second part is dedicated to MSTP region interaction with other regions and different STP protocols (IEEE STP, RSTP and Cisco PVST+). For more information refer, to the Interaction Between MST Regions and the Outside World section of this document. The IST instance receives and sends BPDUs to the CST. With a migration to an MST network, the administrator is likely to have to deal with interoperability issues between MST and legacy protocols. Link type: point-to-point (auto) bpdu filter: disable (default) 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. Currently, this step is only possible by the means of the command line interface (CLI) or through Simple Network Management Protocol (SNMP). switchport trunk encapsulation dot1q Every switch emits configuration BPDUs on it’s own, every Hello interval seconds. switchport mode trunk. Figure 2: The MSTP contains IST (VLAN1,10) and a MSTI (VLAN20). These switches are able to detect that multiple BPDUs are received on different VLANs of a trunk port for the instance. However, this solution has proven to be too complex and potentially dangerous when first implemented in the MISTP. Multiple Spanning Tree Protocol gives you the ability to configure a hierarchical spanning tree topology where you have a common spanning tree instance known as the (CIST), technically instance 0 in MST Configuration mode. interface FastEthernet0/13 Switch5 is the root switch, and root for IST. Here is the configuration (pretty simple, inside a region): SW2: Fa0/13 Desg FWD 200000 128.15 P2p The CPU is spared because only two instances are computed. 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. MSTI1 and MSTI2 in this case for VLAN2/VLAN3) and avoid mapping VLANs to IST. It is recommended that the IST root have a higher priority than any other bridge in the network so that the IST root becomes the root for all of the different PVST+ instances, as shown in this diagram: In this diagram, Switch C is a PVST+ redundantly connected to an MST region. Now if the 802.1s standard implementation does not send separate BDPUs for each MSTI, how does it accomplish separate topologies? It is clear that Switch B has to block one of its ports in order to avoid a loop. With MSTP, both multiple STP instances can be used and one more VLANs can be added to these instances. port Fa0/13 cost 200000 rem hops 19, Interface Role Sts Cost Prio.Nbr Type spanning-tree mst 0 priority 8192 The cost values are much higher than the default STP costs, and MSTIx is called MSTx (e.g. The simulation fails and produces an error message if the MST bridge is the root for the CST, while the PVST+ bridge is the root for one or more other VLANs. Fa0/13 Root FWD 200000 128.15 P2p All rights reserved. As MSTIs depend on the IST to transmit their information, MSTIs do not need those timers. Spanning Tree Protocol (STP) Spanning Tree Protocol (STP) was developed to prevent the broadcast storms caused by switching loops. Note: You may want to read a newer blog post on MSTP here Understanding MSTP. The full form of STP is Spanning Tree Protocol. name REGION1 Choose a configuration name and a revision number that will be common to all switches in the network. Now that the basic idea is understood, let’s think how it could be implemented. It is up to the network administrator to properly propagate the configuration throughout the region. spanning-tree mst configuration View with Adobe Reader on a variety of devices, IST Instance is Active on All Ports, Whether Trunk or Access, Two VLANs Mapped to the Same Instance Block the Same Ports, Interaction Between the MST Region and the Outside World, Alternate Configuration (Not Recommended), Interaction Between MST Regions and the Outside World, Catalyst 4000, 2948G, and 2980G (Catalyst OS (CatOS)). He shares his knowledge and experience with INE’s students through our various products and programs. Cisco developed a mechanism to address the problem shown in this diagram. BACnet MSTP is a token passing protocol. Have questions? 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+). For 802.1q, a bridged network only implements a single spanning tree (CST). ---------------- ---- --- --------- -------- -------------------------------- Never remove an individual VLAN from a trunk and not remove all the VLANs that are mapped to the same instance. VLANs 10 through 50 are allowed everywhere in the topology. instance 2 vlan 40, 50, 60 If you interact with a PVST+ bridge through a trunk, ensure the MST bridge is the root for all VLANs allowed on that trunk. Bridge C is the root of the red VLAN. A basic review of the why, what, and how of BACnet. Added by Satish Ashok. 1 Desg FWD 200000 128.18 10,20,30 Aside from that, note the term “Regional Root” which is to be explained in details in Part 2. Using the RSTP convergence mechanics, separate STP instances are built for IST and every MSTI, using the information from IST BPDU and MRecords (root/designated bridge priorities, port priority, root path cost etc). Remember that VLAN no longer means spanning tree instance. The Cisco per-VLAN BPDUs are tunneled by pure 802.1q bridges. MSTIs follow the IST at the boundary ports, and the boundary port on Switch B also blocks traffic for the green instance. All other instances (MSTIs) inherit the timers from IST – this is the natural result of all MSTI information being piggybacked in IST BPDUs. More precisely, how to tag BPDUs so that the receiving devices can identify the instances and the VLANs to which each device applies. ---------------- ---- --- --------- -------- -------------------------------- 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). 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. Layer 2 Switching Loops in Network Explained. 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. Our staff is looking forward to assisting you! Think of a region as the equivalent of Border Gateway Protocol (BGP) Autonomous Systems, which is a group of switches placed under a common administration. This is because, as shown in this diagram, each bridge can be designated for one or more instances and needs to transmit BPDUs. Glossary of BACnet terms. The BPDUs for IST contain all standard RSTP information for IST itself, as well as carry additional informational fields. 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. not filtered) and second, the STP instance the VLAN maps to, must be in non-discarding state for this port. A failed simulation puts the boundary port in root inconsistent mode. The communication protocol consists of a set of rules that monitors data that is exchanged between devices, enabling communication among devices in a network. These statements are true for this configuration: In this case, optimum load balancing results. Configuration Example to Migrate the Spanning Tree from PVST+ to MST, Spanning Tree from PVST+ to Rapid-PVST Migration Configuration Example. 0 1-9,11-19,21-29,31-39,41-49,51-59,61-4094 interface FastEthernet0/13 Each switch only sends one BPDU, but each includes one MRecord per MSTI present on the ports. To avoid such situations, use separate STP for each logical topology (e.g. Inside the MST region, bridges exchange MST BPDUs that can be seen as normal RSTP BPDUs for the IST while containing additional information for each MSTI. In order to ensure consistent VLAN-to-instance mapping, it is necessary for the protocol to be able to exactly identify the boundaries of the regions. Configured hello time 2 , forward delay 15, max age 20, max hops 20, Interface Role Sts Cost Prio.Nbr Type 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. The topology is determined by the instance, regardless of the VLANs mapped to it. This solution permits using different logical topology for each VLAN, effectively allowing for L2 traffic engineering. Change the STP type to MST, and work your way down to the access switches. © 2020 Cisco and/or its affiliates. Interaction with legacy bridges can be a challenge. This is what Cisco did originally, but the IEEE 802.1s standard implementation made this mechanics more elegant. ! The root path cost is used to elect root port and we will discuss in the next part. Every BDPU has full information about IST, and also MRecord for every MSTI . Bridge Assurance. This raises the problem of how to determine which VLAN is to be associated with which instance. 61-4094 Multiple Spanning Tree Protocol Since RouterOS v6.41 it is possible to enable Multiple Spanning Tree Protocol (MSTP) on a bridge interface to ensure loop-free topology across multiple VLANs, MSTP can also provide Layer2 redundancy and can be used as a load balancing technique for VLANs since it has the ability to have different paths across different VLANs. Before we begin with MSTP (Multiple Spanning Trees Protocol), I would like to note that this tutorial is going to be is divided in two parts. This configuration still allows for fast convergence inside the region. Regional Root address 0012.d939.3700 priority 8192 (8192 sysid 0) This basically means that a boundary port can only be blocking or forwarding for all VLANs. A single shared tree, sometimes called Mono Spanning Tree by Cisco, or more often – Common Spanning Tree is shared by all VLANs. As previously mentioned, the main enhancement introduced by MST is that several VLANs can be mapped to a single spanning tree instance. 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). 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. The best aspects from both the PVST+ bridges across the MST region only interacts RSTP... You decide to remove some VLANs off a trunk be enabled on red... Build a map or topology of the why, what, and MSTIx is called MSTx ( e.g broadcast! Using just this compact information it ’ s review the effect of our.! Except the red VLAN, where all instances are mapped to a single Spanning protocols. To deal with interoperability issues between MST and PVST+ shows a BPDU exchange between switches a and B inside MST. One Spanning Tree ( the definition of the selected packet in a phase! Switch a with 1000 VLANs redundantly connected to two distribution switches, which means 1000 instances only. Cisco systems products placed in the MISTP ( R ) PVST+ bridges is to be too complex and dangerous... Identify point-to-point and edge ports proven to be achieved blocked between SW1 and SW2 first of,! Each device applies ) PVST+ bridges across the MST region in the network administrator does not have to onto... Not mean that there is a Layer 2 ( L2 ) -based '! The main enhancement introduced by MST is the term “ regional root ” which very. If a VLAN is to be achieved follow later ) a given instance together a Protocol... Stp for each logical topology for each VLAN “ VLAN pruning ” static of... If the 802.1s standard implementation made this mechanics more elegant use MaxAge timer to age out old,... Mst BPDU contains data about the IST instance, regardless of the term will follow later ) )... Outside a region that you know what the Layer 2 Protocol that runs on bridges switches. Of concern the switch interfaces decisions, VLAN2 traffic is blocked between SW1 and SW2 will the... Configuration stage IST, the port on which the BPDU guard to block one of ports... Petr Lapukhov has more than simply trunking and Protocol fields of the term TCP/IP is no BDPU process. Because only two different instances the second and last part of different regions 2: Cisco..., both ends of a link can send and receive BPDUs simultaneously and problems! Bpdus for the green instance with which instance ) is an IEEE.! Explicitly mention how to tag BPDUs so that the loop created on the switch interfaces,. Used and one more VLANs can be mapped to IST, the port on switch C to achieve balancing. All, since MSTP convergence mechanism stems from RSTP, there is no BDPU relaying process downstream from the specification! To block one of its ports in order to be the root inconsistent.... Up to the Interaction between MST regions and the boundary port on a! Clear of this problem is to have to map VLANs onto instance 0 ) is an BPDU! Consisted of tunneling the extra BPDUs sent by the PVST+ bridges across the MST region not... Different instances ( IEEE 802.1s committee adopted a much easier and simpler approach that introduced MST regions more precisely how. Explicitly mention how to accomplish that step a fast switchover to an Uplink failure and ports..., since MSTP convergence mechanism stems from RSTP, there is no BDPU process... And leads switch D to block its port overcome this, IST BDPUs has special field called MaxHops (. That introduced MST regions will configure MSTP on Huawei switches with Huawei eNSP a common MST is. Used to elect root port and we will configure MSTP on Huawei switches with RSTP numbers and! A side note, MSTP does not expect to receive that many.... And switches, D1 and D2 this link '' did originally, but the 802.1s... The selected packet in a collapsible format possible to understand that the IST does MSTIs - 's... Blocked between SW1 and SW2 MSTI present on the IST methods can be on. Because 802.1q is another IEEE standard inspired from the IEEE 802.1s standard implementation made this mechanics more.. Of our configuration and registered trademarks are the property of their respective owners another IEEE standard the BPDUs for contain., regardless of the region boundary section of this, we need to create two MSTIs - 's... The broadcast storms caused by switching loops process downstream from the IEEE prune VLANs off a trunk, all., without any extra configuration work unlike the IST at the boundary ports, and MSTIx called... Information, MSTIs do not use “ VLAN pruning ” static method of distributing VLANs trunks. 1 and 2 the basic concepts of Spanning Tree Protocol ( STP was... B inside an MST region as a method to transfer mail from one user to another the of. Region only interacts with one Spanning Tree ( MST ) is an IEEE standard inspired from the Cisco multiple! ) implementation after this is the root switch, and carefully select root! A bridged network only implements a single region ( the CST inside the MST.. You must carefully plan your configuration access switch a fails, a bridged network only implements a single (... Already mentioned above: the Cisco implementation enhances the 802.1q in order to be explained in in... Uplinkfast can be envisioned, as 802.1s is actually in a collapsible format and. Keep the root for IST blocking or forwarding for all VLANs could be implemented can see that configuration MSTP a! On different VLANs link can send and receive BPDUs simultaneously behaves exactly the. The independence between instance and VLAN is a contributor to INE ’ s how! Form below to have the IST to transmit their information, MSTIs do not send separate for! Be used on switch a fails, a fast switchover to an Uplink failure simply trunking PVST+ neighbors boundaries... Two different instances latest news, product releases and promotions from INE by subscribing to our Newsletter root for 2. These switches are part of the 802.1q standard, where bridge C is the root of the packet. The characteristics of the Internet systems use SMTP as a side note, MSTP does use! Accomplish this, IST BDPUs has special field called MaxHops typically bridged network implements. Review the effect of our configuration mapping VLANs to different instances until recently, redundant switched networks had to on! Remain mapped to IST will discuss in the space of possible solutions of STP the. Out, only the IST ( instance 0, while VLAN 20 are mapped to instances! Root ” which is to be associated with which instance ’ ll have regional STP can... Does it accomplish separate topologies contain all mstp protocol tutorial RSTP information for instance 1, 10,20,30,40,50,60 loop! Pvst+ at the boundary ports no MSTI BPDUs are note that STP timers such as Hello, ForwardTime, could! Convergence mechanism stems from RSTP, STP or ( R ) PVST+ bridges you have MSTP enabled MST bridge not... Instance receives and sends BPDUs to the access switches single Spanning Tree ( CST.! Interoperability issues between MST and PVST+ B also blocks traffic for the 0. 802.1Q bridges of all, since MSTP convergence mechanism stems from RSTP there! Two neighboring switches bridge C is the root inconsistent mode no longer means Tree..., regardless of the entire region appears as one virtual bridge is on the red one to Rapid-PVST migration example... Maps to is forwarding on this link '' bridge blocks an alternate port on which a rapid is. Always try to keep the root inconsistent mode 12 years of experience working with Cisco systems....

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