Stp timers

Max Age — Maximum period of time that passes before a bridge port saves a configuration BPDU info, 20 sec by default — tune-able between 6 — 40 seconds. Message Age — not a fixed value, the length of time that has passed since the root bridge initially originated the BPDU. When Root bridge sends it, its value is 0 and increments after every bridge-hop. The age time starts at the message age that is received in that configuration BPDU.

IF this age timer reaches max age before another BPDU is received that refreshes the timer, the info is aged out for that port. Diameter of the STP domain dia — Maximum number of bridges between any 2 points on topology any two points of end hosts attachment. IEEE recommends 7 with default timers. Local latency. IEEE says it should be maximum 1 seconds. IEEE recommended 1 second maximum. Message age increment over-estimate msg overestimate — This is the increment that each bridge adds to the message age before forwarding the BPDU.

Cisco switches add 1 second. IEEE recommendation is 1 second. It is also the time between CPU decision to send a frame and the moment when the frame effectively begins to leave the bridge. IEEE says 0. Maximum frame lifetime — maximum time a frame that was previously sent to the bridge network remains in the network before the frame reaches that destination.

Maximum transmission halt delay — time that is necessary in order to effectively block a port after the decision to block is made — 1 seconds max transmission halt delay. In addition, we need to count the same delay that we use to count max age.

Time for last bridge to stop forwarding frame that are received on the previous topology max trans halt delayuntil the last frame that is forwarded on the previous topology disappears max frame lifetime. The other parameters should be considered fixed and non-tune-able.

The formula comes out to be be:.

stp timers

But, doubles the repletion and increases load on switches. Several switches and trunks will definitely add more load to the CPU. You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account.Nowadays we see more and more routing in our networks.

To keep up with the speed of these routing protocols another flavor of spanning-tree was created… rapid spanning-tree. Rapid spanning-tree is not a revolution of the original spanning-tree but an evolution. Take a look at the picture below:. Remember the port states of spanning-tree?

We have a blocking, listening, learning and forwarding port state. This is the first difference between spanning-tree and rapid spanning-tree. Rapid spanning-tree only has three port states:. You already know about learning and forwarding but discarding is a new port state. Basically it combines the blocking and listening port state. Do you remember all the other port roles that spanning-tree has? The other switches non-root have to find the shortest cost path to the root bridge.

This is the root port. The next step is to select the designated ports:. The port will become the designated port if it can send the best BPDU. SW1 as a root bridge will always have the best ports so all of interfaces will be designated.

The interfaces that are left will be blocked:. Let me show you a new example with a port state that is new for rapid spanning-tree:. You are very unlikely to see this port on a production network though.

The BPDU is different for rapid spanning-tree. In the classic spanning-tree the flags field only had two bits in use:. All bits of the flag field are now used. The role of the port that originates the BPDU will be added by using the port role field, it has the following options:. Switches running the old version of spanning-tree will drop this new BPDU version. In case you are wondering…rapid spanning-tree and the old spanning are compatible! Rapid spanning-tree has a way of dealing with switches running the older spanning-tree version.

BPDUs are now sent every hello time. Only the root bridge generated BPDUs in the classic spanning-tree and those were relayed by the non-root switches if they received it on their root port. Rapid spanning-tree works differently…all switches generate BPDUs every two seconds hello time. This is the default hello time but you can change it.

The classic spanning-tree uses a max age timer 20 seconds for BPDUs before they are discarded. Rapid spanning-tree works differently!You are not advised to directly change the preceding three timers. The three parameters are relevant to the network scale; therefore, it is recommended that you set the network diameter so that the spanning tree protocol automatically adjusts these timers.

When the default network diameter is used, the three timers also retain their default values. To prevent frequent network flapping, make sure that the Hello Time, Forward Delay, and Max Age timer values conform to the following formulas:. Setting the STP Timers Context The following timers are used in spanning tree calculation: Forward Delay: specifies the delay before a state transition.

After the topology of a ring network changes, it takes some time to spread the new configuration BPDU throughout the entire network. As a result, the original blocked port may be unblocked before a new port is blocked. When this occurs, a loop exists on the network.

Setting the STP Timers

You can set the Forward Delay timer to prevent loops. When the topology changes, all ports will be temporarily blocked during the Forward Delay. Hello Time: specifies the interval at which hello packets are sent. A device sends configuration BPDUs at the specified interval to detect link failures. To prevent frequent network flapping, make sure that the Hello Time, Forward Delay, and Max Age timer values conform to the following formulas: 2 x Forward Delay - 1.

Procedure Run system-view The system view is displayed. Run stp timer forward-delay forward-delay The Forward Delay timer is set for the switching device.

By default, the Forward Delay timer is centiseconds 15 seconds. Run stp timer hello hello-time The Hello Time is set for the switching device. By default, the Hello Time is centiseconds 2 seconds. Run stp timer max-age max-age The Max Age timer is set for the switching device. By default, the Max Age timer is centiseconds 20 seconds.All the same Lynda. Plus, personalized course recommendations tailored just for you. All the same access to your Lynda learning history and certifications.

Same instructors. New platform. Observe how Spanning Tree Protocol transitions ports through several states to safely begin forwarding frames in a loop-free fashion. Discover the three timers utilized by traditional STP. Understand how these timers are used to carefully transition ports through the various STP states, as well as their role in reacting to topology changes.

No MAC address learning occurs…on the interface either. Are you sure you want to mark all the videos in this course as unwatched? This will not affect your course history, your reports, or your certificates of completion for this course. Type in the entry box, then click Enter to save your note.

Packet Magnifier

Start My Free Month. You started this assessment previously and didn't complete it. You can pick up where you left off, or start over. Develop in-demand skills with access to thousands of expert-led courses on business, tech and creative topics.

Video: STP states and timers. You are now leaving Lynda. To access Lynda. Visit our help center. Network Administration. Preview This Course. Resume Transcript Auto-Scroll. Author Greg Sowell. Here, Greg covers the fundamentals of switch network design, as well as SDM templates, switchport configuration and troubleshooting, and discovering connected devices. Skill Level Advanced.

Show More Show Less.These timers can be configured to affect STP convergence. However, you are not advised to directly change these timers. Instead, it is recommended that you set the network diameter so that the spanning tree protocol automatically adjusts these timers in accordance with the network scale. To prevent frequent network flapping, make sure that the Hello Time, Forward Delay, and Max Age timer values conform to the following formulas:.

The following timers are used in spanning tree calculation: Forward Delay: specifies the delay before a state transition. After the topology of a ring network changes, it takes some time for the new configuration BPDU to spread throughout the entire network. As a result, the original blocked port may be unblocked before a new port is blocked, creating a loop on the network. The purpose of the Forward Delay timer is to prevent loops. When the topology changes, all ports will be temporarily blocked during the Forward Delay.

Hello Time: specifies the interval at which hello packets are sent. A device sends configuration BPDUs at the specified interval to detect link failures. To prevent frequent network flapping, make sure that the Hello Time, Forward Delay, and Max Age timer values conform to the following formulas: 2 x Forward Delay - 1. Procedure Run system-view The system view is displayed. Run stp timer forward-delay forward-delay The Forward Delay timer is set for the device.

By default, the Forward Delay timer is centiseconds 15 seconds. Run stp timer hello hello-time The Hello Time is set for the device. By default, the Hello Time is centiseconds 2 seconds. Run stp timer max-age max-age The Max Age timer is set for the device. By default, the Max Age timer is centiseconds 20 seconds. Run commit The configuration is committed.Understanding Multiple Spanning Tree Protocol Understanding Rapid Spanning Tree Protocol This document assumes a good understanding of STP.

If you are unfamiliar with STP, changes that you make can cause any of these occurrences:. Refer to Refer to Cisco Technical Tips Conventions for more information on document conventions. This time is equal to 2 seconds sec by default, but you can tune the time to be between 1 and 10 sec. This time is equal to 15 sec by default, but you can tune the time to be between 4 and 30 sec. This time is 20 sec by default, but you can tune the time to be between 6 and 40 sec.

Each configuration BPDU contains these three parameters. In addition, each BPDU configuration contains another time-related parameter that is known as the message age. The message age is not a fixed value. The message age contains the length of time that has passed since the root bridge initially originated the BPDU. The root bridge sends all its BPDUs with a message age value of 0, and all subsequent switches add 1 to this value.

stp timers

Effectively, this value contains the information on how far you are from the root bridge when you receive a BPDU. This diagram illustrates the concept:. The age timer begins to run.

The age timer starts at the message age that is received in that configuration BPDU.

stp timers

If this age timer reaches max age before another BPDU is received that refreshes the timer, the information is aged out for that port. On the port that goes to A, the information ages out in max age — 0 sec. This time is 20 sec by default. On the port that goes to A, the information ages out in max age — 1 sec. This time is 19 sec by default.

27 STP timers

On the port that goes to E, the information ages out in max age — 2 sec. This time is 18 sec by default. IEEE This is logically the latency through the bridge. The IEEE recommendation is to consider 1 sec as the maximum bridge transit delay. The IEEE recommendation is to use 1 sec for this parameter.

It is the time between the CPU decision to send a frame and the moment when the frame effectively begins to leave the bridge. The IEEE recommendation is to use 0. From these parameters, you can calculate other values. This list provides the additional parameters and the calculations. The calculations assume that you use the default recommended IEEE values for all parameters.

Assume a diameter of seven hops, three BPDUs that can be lost, and a hello time of 2 sec. In this case, the formula is:. Message age overestimate —The purpose of this parameter is to account for the age of the BPDU since origination. Assume that each bridge increases the BPDU message age by 1 sec. The formula is:.You can:.

If an STP request is issued for another processor operations connection type, it will be rejected. Requirements The requirements for the STP command to complete successfully are: Processor operations must be active.

The addressed target system must be initialized, or if the target hardware is addressed, at least one target system on that hardware must be initialized.

The target system cannot be the CTS. The target system must be the CTS.

STP Timers and Topology Change Notifications

The target system must be the system that will become the CTS. Note that the active DST settings cannot be queried. This is a z System API limitation. The string must not exceed eight characters. It bypasses a number of validity checks on server connectivity, and it allows the configuration of servers that may not be in POR-complete state or do not yet have coupling link connectivity to the selected CTS. NO Specifies that various verifications will be made before allowing the configuration to be set.

If the connections are not there, the configuration will fail. YES Specifies that the configuration will be applied without verifications. It defines the CTN time to run with the daylight saving time either enabled or disabled. Config Specifies the type of server that a configuration is being set for. This is the server that is assigned to take over as the CTS, either because of a planned or unplanned reconfiguration.

This is usually a Stratum 2 server that should be attached to the Preferred Time Server as well as all the servers that are attached to the Preferred Time Server. This is the server that is assigned to provide additional means for the Backup Time Server to determine whether it should take over as the Current Time Server.

The only values that are allowed are Preferred or Backup. Parent topic: Common Commands.


Comments

Leave a Reply

Your email address will not be published. Required fields are marked *