What is the extended system ID?
The extended system ID value is added to the bridge priority value in the BID to identify the priority and VLAN of the BPDU frame. When two switches are configured with the same priority and have the same extended system ID, the switch having the MAC address with the lowest hexadecimal value will have the lower BID.
Can spanning tree cause problems?
Spanning Tree is not inherently bad or wrong, but it does have many limitations in its design and operation. The most serious shortcoming is that STP has a brittle failure mode that can bring down entire data center or campus networks when something goes wrong.
What causes spanning tree to block?
The most common reason for disabling spanning tree is that the original 802.1D Spanning Tree Protocol (STP) goes through a fairly lengthy wait period from the time a port becomes electrically active to when it starts to pass traffic.
What is the bridge ID in STP?
Every switch has an identity when they are part of a network. This identity is called the Bridge ID or BID. It is an 8 byte field which is divided into two parts. The first part is a 2-byte Bridge Priority field (which can be configured) while the second part is the 6-byte MAC address of the switch.
How do I set priority in STP?
To ensure that a switch has the lowest bridge priority value, use the spanning-tree vlan vlan-id root primary command in global configuration mode. The priority for the switch is set to the predefined value of 24,576 or to the highest multiple of 4096 less than the lowest bridge priority detected on the network.
What is spanning tree vlan priority?
The spanning tree port priority range is from 0 to 255, configurable in increments of 4. The default value is 128. Cisco software uses the port priority value when an interface is configured as an access port and uses VLAN port priority values when an interface is configured as a trunk port.
What are the disadvantages of Spanning Tree Protocol?
One of the drawbacks of an STP is that in blocking redundant ports and paths, a spanning tree reduces the aggregate available network bandwidth significantly. Additionally, STP can result in circuitous and suboptimal communication paths through the network, adding latency and degrading application performance.
Why is STP rarely used?
Because of its cost and difficulty with termination, STP is rarely used in Ethernet networks.
How do I know if a port is spanning tree blocking?
If you just have command line access to your switches, jump on one of your switches and do show spanning tree there. That will tell you which is the root bridge. To find the entire topology, and to see which ports are forwarding and which are blocking, you really just have to map it out switch by switch.
When should you disable STP?
You can enable or disable STP on the following levels:
- Globally – Affects all ports and port-based VLANs on the device.
- Port-based VLAN – Affects all ports within the specified port-based VLAN.
- Individual port – Affects only the individual port.
What is the difference between root ID and bridge ID?
The bridge ID is the mac-address of the switch you are on. The root ID is the mac-address of the switch that is the root bridge for that vlan. So if the bridge ID and root ID are the same then you are on the root bridge for that vlan.
What are the 4 states of the spanning tree protocol?
STP Port States
Blocking – When a device is connected, the port will first enter the blocking state. Listening -The switch will listen for and send BPDUs. Learning – The switch will receive a superior BPDU, will stop sending its own BPDUs, and will relay the superior BPDUs. Forwarding – The port is forwarding traffic.
What is the highest STP priority?
The priority range is 0 to 61440 in increments of 4096. The default is 32768. The lower the number the more likely the switch will be chosen as the root switch.
What are the 4 states of the Spanning Tree Protocol?
What is STP failure?
It happens when STP erroneously moves one or more ports into the forwarding state. Remember that an Ethernet frame header does not include a TTL field, which means that any frame that enters a bridging loop continues to be forwarded by the switches indefinitely.
Is Spanning Tree Protocol still used?
Spanning Tree Protocol (STP) is dead, or at least it should be. It’s too slow to converge when there’s a change, and it causes issues with performance because there is only one forwarding path.
How does STP decide which port to block?
The STA considers both path and port costs when determining which ports to block. The path costs are calculated using port cost values associated with port speeds for each switch port along a given path. The sum of the port cost values determines the overall path cost to the root bridge.
Should I enable STP on router?
The need for STP occurs when your router is being used in a mesh network with multiple WDS-enabled repeaters, or in an ad hoc network with multiple ad hoc connections. If your router is not being used in either of the given scenarios, then likely STP is not necessary.
Should I enable STP on switch?
STP protects your network in case two switch ports are connected together, so you should use it generally. With a single switch, you can have redundant links to an appropriately configured host.
Does STP use BPDU?
STP uses two types of BPDUs, configuration BPDUs and topology change notification (TCN) BPDUs.
Why root bridge is used in STP?
The root bridge is selected by manually configuring its bridge priority to a low value. 32768 is the default value out of a range from 0 to 61440. If all switches in a single spanning tree have the same bridge priority, the switch with the lowest MAC address will become the root bridge.
What is STP and its types?
STP—Defined in IEEE 802.1D, this is the original standard that provided a loop-free topology in a network with redundant links. Also called Common Spanning Tree (CST), it assumed one spanning-tree instance for the entire bridged network, regardless of the number of VLANs.
What are the two types of Spanning Tree Protocol?
Different types of Spanning Tree Protocol
- The original STP (802.1D) It is also referred to as the Common STP, standardized as 802.1D.
- Per VLAN spanning tree (PVST) and PVST+ It is the advancement or the modification by Cisco to the 802.1d standard.
- Rapid Spanning Tree Protocol (RSTP)
- Rapid PVST and Rapid PVST+
What is the lowest priority for STP?
How do you troubleshoot a STP loop?
Action Plan:
- Implement Spanning Tree PortFast and BPDUGuard on all edge ports.
- Verify that currently the proper switch is STP root for all VLANs.
- Enable loop guard on all distribution/access layer switches*
- Enable BPDU guard on all distribution/access layer switches*
- Enable UDLD on all fiber uplinks*