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. Carefully decide how many instances are needed in the switched network, and keep in mind that an instance translates to a logical topology. Just as a side note, MSTP does not use MaxAge timer to age out old information, like RSTP/STP do. The BPDUs for IST contain all standard RSTP information for IST itself, as well as carry additional informational fields. Aside from that, note the term “Regional Root” which is to be explained in details in Part 2. The single spanning-tree instance used by IEEE and per-VLAN STP implemented by Cisco represents two poles in the space of possible solutions. The IST instance receives and sends BPDUs to the CST. Unlike regular converged spanning tree topology, both ends of a link can send and receive BPDUs simultaneously. A detailed technical description of how BACnet devices may communicate using the Internet protocols. ---------------- ---- --- --------- -------- -------------------------------- 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. In addition to expanding each selection, you can apply individual Wireshark filters based on specific details and follow streams of data based on protocol type by right-clicking the desired item. Why a Standard Protocol? The issue is irrelevant in the case of the 802.1q standard, where all instances are mapped to a unique instance. Therefore, MST must be able to interact with 802.1q-based networks, because 802.1q is another IEEE standard. Cisco developed a mechanism to address the problem shown in this diagram. Consider the following example: In this topology, VLANs are manually pruned on trunks. Boundary : internal bpdu guard : disable (default) 61-4094 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. Each switch only sends one BPDU, but each includes one MRecord per MSTI present on the ports. Always try to keep the root of the CST and IST inside the region. ! This tutorial is the second and last part of the article "Layer 2 switching loop: - causes and solutions". interface FastEthernet0/16 Contact an INE Training Specialist today! 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. 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. switchport mode trunk ! The MST region replicates the IST BPDU on all the VLANs to simulate a PVST+ neighbor. A BACnet device is often comprised of a microprocessor-based controller and software combination that is designed to understand and use the BACnet protocol. 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? The switch forwarding logic for VLAN traffic was changed a little bit. 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. switchport mode trunk. 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. Figure 2: The MSTP contains IST (VLAN1,10) and a MSTI (VLAN20). MSTP technology is the result of multiple technical forms and integrations, which fully utilizes a GFP (Generic Frame Protocol) data encapsulation, virtual concatenation mapping and RPR. 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). The full form of STP is Spanning Tree Protocol. 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). The old MaxAge/ForwardDelay timers are still used when MSTP interacts with RSTP, STP or (R)PVST+ bridges. This solution permits using different logical topology for each VLAN, effectively allowing for L2 traffic engineering. 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. First, a short history tour. ! Boundary : internal bpdu guard : disable (default) This configuration results in pcA 's inability to send frames to pcB. switchport trunk encapsulation dot1q 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). For 802.1q, a bridged network only implements a single spanning tree (CST). Operational hello time 2 , forward delay 15, max age 20, txholdcount 6 Bridge address 0019.5684.3700 priority 32770 (32768 sysid 2) From an end-user's perspective, the main drawbacks associated with a migration to MST are: The protocol is more complex than the usual spanning tree and requires additional training of the staff. MSTP is based on EIA-485 and within the same unified standard it provides a sophisticated routing capability allows scaling of BACnet inter networks into large and efficient systems. Let’s review the effect of our configuration. IST is MST0). This means that Bridge B is designated for all VLANs except the red one. ------------------------------------------------------------------------------- Cisco also answered large Layer 2 (L2)-based networks' scalability issues with the development of the MISTP. There is no need to run 1000 instances. 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 One spanning tree instance for each VLAN is maintained, which means 1000 instances for only two different final logical topologies. The boundary MST bridge does not expect to receive that many BPDUs. Page 6 | Spanning Tree Protocols: STP, RSTP, and MSTP Spanning Tree Protocol (STP) STP uses the process described in Table 1 on page 4, to avoid loops. The IST Instance is Active on All Ports, Whether Trunk or Access section illustrates some common pitfalls and how to avoid them. interface FastEthernet0/13 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. 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. STP was originally defined in IEEE 802.1D. The terminology continues to evolve, as 802.1s is actually in a pre-standard phase. 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. This feature behaves exactly as the PVST in this example. switchport trunk encapsulation dot1q The UDP side of the stack operates in parallel to TCP, and is automatically included in most implementations of an Ethernet based protocol stack. 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)). instance 1 vlan 10, 20, 30 Each BDPU contains instance number and a list of VLANs, mapped on sending switch to this particular instance – this allows for consistency check. This diagram shows a problem that is a variant of the one discussed in the IST Instance is Active on All Ports, Whether Trunk or Access section: Suppose that VLANs 10 and 20 are both mapped to the same instance (instance 1). In order to clearly understand the role of the IST instance, remember that MST originates from the IEEE. (WARNING: it might be dropped in the future and replaced by theAutoIsolate feature of 802.1Q-2011) 3. Different paths … 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. Bridge C is the root of the red VLAN. This document assumes that the reader is familiar with Rapid STP (RSTP) (802.1w), as MST heavily relies on this other IEEE standard. BPDUs for the green instance are not sent out of the MST region. This is a typical misconfiguration problem. 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. The IST can represent the entire MST region as a CST virtual bridge to the outside world. This makes it possible to understand that the virtual bridge blocks an alternate port on B. Root address 0012.d939.3700 priority 8192 (8192 sysid 0) 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. This configuration still allows for fast convergence inside the region. Regional Root address 0012.d939.3700 priority 8192 (8192 sysid 0) In this lesson, we will configure MSTP on Huawei switches with Huawei eNSP. 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. This diagram shows a common design that features access Switch A with 1000 VLANs redundantly connected to two distribution Switches, D1 and D2. 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