Spanning tree protocols work by creating bridges. A root bridge switch is a bridge at the top of a Spanning Tree. However, some legacy networks require the slower convergence times of basic STP that work with If your network includes Help us improve your experience.
Spanning Tree Protocol. STP overview. Standard STP parameter configuration. STP parameters and defaults. Enabling or disabling STP globally. Enabling or disabling STP on an individual port. Changing STP bridge and port parameters. Changing STP bridge parameters. Changing STP port parameters. STP protection enhancement. Enabling STP protection. Clearing BPDU drop counters.
Displaying STP information. Displaying STP information for an entire device. Displaying STP state information for an individual interface. STP feature configuration. Fast port span. Disabling and re-enabling fast port span.
Excluding specific ports from fast port span. Fast Uplink Span. Active uplink port failure. Switchover to the active uplink port. Bridges and bridge port roles. Edge ports and edge port roles. Point-to-point ports. Bridge port states. Edge port and non-edge port states. Changes to port roles and states. Convergence after a link failure. Convergence at link restoration. Convergence in a complex Propagation of topology change.
Compatibility of Configuring Displaying information about w. Spanning tree reconvergence time. Enabling SSTP defaults. Enabling SSTP. Displaying SSTP information. STP load balancing. Configuration example for STP load sharing. Spanning Tree Path Cost Support for Displaying Spanning Tree PVRST compatibility.
BPDU guard. Enabling BPDU protection by port. Re-enabling ports disabled by BPDU guard. Displaying the BPDU guard status. BPDU guard status example configurations. BPDU guard status example console messages. Root guard. Enabling STP root guard. Displaying the STP root guard. Displaying the root guard by VLAN. Designated Protection. Enabling Designated Protection on a port. Syslog message for a port in designated inconsistent state.
Packet InError Detection. Configuring Packet InError Detection. Syslog message for error-disabled port due to inError packets. Error disable recovery. Enabling an error-disabled port automatically. Enabling an error-disabled port manually. Setting the recovery interval. In this network, a redundant link is planned between Switch A and Switch B.
However, this setup creates the possibility of a bridging loop. For example, a broadcast or multicast packet that transmits from Station M and is destined for Station N simply continues to circulate between both switches. In order to provide this desired path redundancy, as well as to avoid a loop condition, STP defines a tree that spans all the switches in an extended network. STP forces certain redundant data paths into a standby blocked state and leaves other paths in a forwarding state.
If a link in the forwarding state becomes unavailable, STP reconfigures the network and reroutes data paths through the activation of the appropriate standby path.
With STP, the key is for all the switches in the network to elect a root bridge that becomes the focal point in the network. All other decisions in the network, such as which port to block and which port to put in forwarding mode, are made from the perspective of this root bridge.
A switched environment, which is different from a bridge environment, most likely deals with multiple VLANs. When you implement a root bridge in a switching network, you usually refer to the root bridge as the root switch. The roots for the different VLANs can all reside in a single switch or in various switches. You can choose the root switch, or you can let the switches decide, which is risky.
If you do not control the root selection process, there can be suboptimal paths in your network. All the switches exchange information for use in the root switch selection and for subsequent configuration of the network. Bridge protocol data units BPDUs carry this information. Each switch compares the parameters in the BPDU that the switch sends to a neighbor with the parameters in the BPDU that the switch receives from the neighbor.
In the STP root selection process, less is better. Before you configure STP, select a switch to be the root of the spanning tree. This switch does not need to be the most powerful switch, but choose the most centralized switch on the network. All data flow across the network is from the perspective of this switch. Also, choose the least disturbed switch in the network. The backbone switches often serve as the spanning tree root because these switches typically do not connect to end stations.
Also, moves and changes within the network are less likely to affect these switches. After you decide on the root switch, set the appropriate variables to designate the switch as the root switch. The only variable that you must set is the bridge priority. If the switch has a bridge priority that is lower than all the other switches, the other switches automatically select the switch as the root switch.
You can also issue the set spantree portfast command, on a per-port basis. When you enable the portfast variable on a port, the port immediately switches from blocking mode to forwarding mode. However, do not use this command when you have switch-to-switch connection. In this case, the command can result in a loop. The to second delay that occurs during the transition from blocking to forwarding mode prevents a temporal loop condition in the network when you connect two switches.
If they don't have any valid reasons, ask them to implement it. In response to Corey and Chris: Configuring ports to be edge ports portfast in Cisco , reduces the time to establish a connection to just a few seconds. Spanning Tree is usually disabled to speed up connections, since standard Spanning Tree can take seconds to establish a link. There are ways around that, too, depending on your equipment, but that's not what you asked! Corey is spot on, i've had machines that actually have problems XP with spanning tree due the second delay and XP wanting a IP in that first sec and then XP just gives up and tries later.
Possible reason behind why they did that. But Keenan didn't mention what type of hardware we were talking about.
You can always disable spanning-tree with mode portfast, and then enable bpduguard to prevent switching loops. This is also beneficial for detecting rouge switching devices. Be warned that the port will be disabled when a switch is plugged in.
Enabling the port again will require manual intervention. Here we have each of our switches as it's own subnet, with L3 routing between the switches on a separate subnet for that. We don't have STP enabled on any of the ports connected to devices. We have BPDU guard which disables a port in the event of a loopback, packet storm, etc.
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