Cisco 3550 switch stp learning notes

Cisco 3550 switch stp learning notes STP (Spanning Tree Protocol) (IEEE 802.1D) Spanning Tree Protocol-review the working principles of SW: 1. the frame it forwards cannot be modified. create a MAC-PORT ing table based on source MAC learning. forward the frames in the target MAC ing table directly from the corresponding port. for frames without target MAC ing/Target wide (Group) broadcasting, SW learns different commands from all port forwarding (except source port) switches from different interfaces, it selects the latest learned command. · When there is only one physical device connecting two segments, the single point of failure may occur ". Segment: 1.STP: a network medium (network cable/Optical Fiber ). 2. Data encapsulation: User Data carrying layer-4 headers. 3. Routing: A logical subnet. · A redundant network is constructed to avoid single point of failure. · Problems caused by redundant networks: 1. multi-frame replication (waste of bandwidth) is a major problem in multicast. Here, we will note the problems that will arise during redundancy. MAC Address Table Flip 3. broadcast storms prevent redundant networks. block-STP is built to overcome the transparent bridging loop in redundant networks. STP identifies the location where a loop exists in the network and blocks redundant links to implement a loop-free network. · STP adopts the STA (Spanning Tree Arithmetic) algorithm. STA selects a reference point (the root of the Spanning Tree) in the redundant link. It selects the path to be reached and blocks other redundant paths. If the selected path fails, other paths are enabled. (The smaller the election parameters in STP, the better.) You should note that the smaller the value, the better. there are other elections. haha. various STP elections are achieved by exchanging BPDU packets, which are directly encapsulated in Ethernet frames. One root bridge per network (each network has only One root bridge) · root bridge election: Lowest BID (minimum BID) · STP assigns a unique identifier for each SW, it is called BID (Bridge ID ). Composition of BID: 2 (Bridge Priority) + 6 (MAC) = 8 Bytes default Priority: 32768 (0x8000) 2950 or more vswitches Add VLAN numbers to this value. Each vswitch has a baseline MAC Address. Run the following command to see Sw2 # show versionBase ethernet MAC Address: 00: each port of the 0D: 28: 61: 35: 00 switch has a MAC address, which is obtained by adding the port number to the Base (baseline) MAC address. Show interfacef0/1 this command can see the MAC address of the switch port to view STP information -- Sw2 # show spanning-treeSw3 # show spanning-tree brief (for earlier versions) vswitches lower than 2900 use this command-PVST (Per Vlan Stp) Cisco SW is each VLAN by default, one STP, which does not affect each other. · The Priority of some low-end switches (2900) does not contain vlan numbers. · Set the best-performing SW to the root bridge Sw1 (config) # spanning-tree vlan 1-10 root primary (24576 = 0x6000) (establish a priority to become the root bridge) sw2 (config) # spanning-tree vlan 1-10 root secondary (28672 = 0x7000) (back up the root bridge to prevent the priority root bridge from showdown) Sw1 (config) # spanning-tree vlan 1-10 priority 4096 (the setting must be a multiple of 4096) One root port per nonroot bridge (each non-root bridge has a root port) root port (RP): Lowest path cost to root bridge each non-root bridge has only one root port and the port with the minimum overhead required for non-root bridges to reach the root bridge. (Forwarding traffic) RP/DP election method: 1. lowestRID (minimum RID) is SW1 (root bridge) BID2.Lowest path cost to root bridge (minimum path overhead to the root) 3. lowest sender BID (minimum sent BID) 4. lowest sender portID this option is used when two lines are directly connected between two switches (Bridge Protocol Data Unit): the root Bridge sends messages every two seconds. BPDU is a layer-2 protocol. The last number of MAC addresses is 00. (01: 80: c2: 00: 00: 00) · Path Cost: the COST value issued by the root bridge is 0. The COST value is added at the entrance of the next switch, the COST value at the exit remains unchanged. 10 Mbps: 100/100 Mbps: 19/1 Gbps: 4/10 Gbps: 2Sw1 # show interfaces statusSw1 # show spanning-treeduplex full-> P2pduplex half-> ShareSw1 (config-if) # spanning-tree (vlan 1) cost 22 each VLAN can generate a self-generated tree. By changing the COST value of each VLAN, you can select a different root bridge for each VLAN, generate different spanning trees, make full use of the link Sw1 (config-if) # spanning-tree cost 22 to modify the Cost value of all VLANs. The Port ID is composed of priority + Port number to modify the Port priority: the default value is 128Sw1 (config-if) # spanning-tree port-priority 16One designated port per segm. Ent (each Segment has only one specified port) the RP/DP Method in TCP/UDP encapsulation of the network Segment medium in the Segment route is as follows: 1. lowestRID (minimum RID) is SW1 (root bridge) BID2.Lowest path cost to root bridge (minimum path overhead to the root) 3. lowest sender BID (minimum sent BID) 4. lowest sender port ID-all ports of the root bridge are specified ports (DP ). · Specify the port (DP): the port from which the Lowest path cost to root bridge (=) Lowest sender BID is smaller (forwarding traffic) nondesignated ports are blocked (unspecified ports will be blocked) BPDU (Bridge Protocol Data Unit) for all SW involved in STP, they all obtain information about other SW in the network through the exchange of data messages, which is called BPDU. · BPDU functions: 1. election root bridge 2. determine the location of the redundant Path 3. avoid loops by blocking specific ports. 4. announcement of network topology changes 5. monitor the status of the spanning tree. The BPDU is sent once every 2 seconds by the root bridge. In the initial network, each SW considers itself a root bridge and sends a BPDU. When comparing LowestBID and selecting a root bridge, only the root bridge sends a BPDU. Only Forwarding is performed for non-root bridges. · TCN (Topology Change Notification) BPDU are generated when SW detects a Topology Change. · Protocol ID: 0 Version: 802.1D (0) Message Type: (ConfigBPDU = 0x00/tcn bpdu = 0x80) <Non-root bridge has multiple redundant links connected to the root bridge> · root port (RP): Lowest path cost to root bridge (=) Lowest sender BID (=) lowest sender port ID Entry + cost value = issuing value (e.g. 19 ports + 8 ports = 27 ports refer to switches) · port ID (PID): 1 (Pri) + 1 (Port Num) = 2 Bytes128.24 (default priority = 128) Sw1 (config-if) # spanning-tree (vlan 1) port-priority16 modify Port priority (must be a multiple of 16) to be modified on the sender. <STP port selection basis, comparison> Lowest path cost to root bridgeLowest sender BIDLowest sender port ID <BPDU Timer> BPDU multicast address: 01: 80: c2: 00: 00: 00 · Message Age: maximum survival Time (20 S) Hello Time: root bridge continuous sending BPDU interval (2 S) Forward Time: duration of SW staying in listening and learning status (15 S) spanning-tree vlan 1-10 hello-time 3 change the time interval for sending BPDU spanning-tree vlan 1-10 forward-time 13 modify the forward time spanning-tree vlan 1-10 max- age 33 modify the maximum survival time 1. blocking (loss of BPDU detected) max age = 20 S2. listener time (listening) forward delay = 15s3. learning (learning) forward delay = 15 s Listening BPDU learning MAC Frame Forwarding Blocking √ ×× Listening √ ×( election Root/RP/DP) learning √ × Forwarding √ <STP Topology Change> · when the following event occurs, SW sends TCN: 1. link failure (FWD-> BLK) 2. the port enters the forwarding status, and SW already has DP3. the non-root bridge receives TCN from its DP, and forwards it to tcn bpdu, which contains only three fields: pro id, version, message, that is to say, the first three fields of the BPDU Flags: TC (Topology Change) tc bpdu will only be generated by the Root user for the work done by the Root bridge (Topology Change Acknowledge): 1. convergence Current Network; 2. aging-time: converts the Aging time of the MAC address table to Forward time <STP and 802.1Q> · in a Trunk using 802.1Q, SW maintains an STP for each VLAN allowed in the Trunk. (PVST) · for SW that does not support 802.1Q, all VLANs maintain one STP. (SSTP)-In the switching network, STP is always running. If the link does not have Trunking. STP only maintains VLAN1 information. Per VLAN Spanning Tree advantages: 1. Vlan-based load root; disadvantages: 1. BPDU are run based on Vlan;