This example shows how to enable PortFast on port 1 of module 4 of a trunk port, bring the trunk port to a forwarding state, and verify the configuration the PortFast status is shown in the "Fast-Start" column :.
Note When you enable PortFast between two switches, the system will verify that there are no loops in the network before bringing the blocking trunk to a forwarding state. To disable PortFast on a switch or trunk port, perform this task in privileged mode:.
To reset PortFast on a switch or trunk port to its default settings, perform this task in privileged mode:. This example shows how to reset PortFast to its default settings on port 1 of module The port configuration overrides the global configuration unless the port configuration is set to default.
If the port configuration is set to default, the global configuration is checked. If the port configuration is enabled, the port configuration is used and the global configuration is not used. By default, BPDU filtering is set for each port. The following sections describe how to configure the UplinkFast feature on the switch. When you enable UplinkFast on the switch, UplinkFast processing is enabled and the spanning tree bridge priority for all VLANs is set to 49,, making it unlikely that the switch will become the root switch.
The spanning tree port cost and port-VLAN cost of all ports on the switch is increased by Enter the all-protocols on keywords on switches that have UplinkFast enabled, but do not have protocol filtering enabled, and that are connected to upstream switches in the network that have protocol filtering enabled.
The all-protocols on keywords cause the switch to generate multicasts for each protocol-filtering group. On switches with both UplinkFast and protocol filtering enabled, or if no other switches have protocol filtering enabled, you do not need to use the all-protocols on keywords.
This example shows how to enable UplinkFast with a station-update rate of 40 packets per ms and verify that UplinkFast is enabled:. To disable UplinkFast and restore the default spanning tree bridge priority, port cost, and port-VLAN cost values to their default values, enter the clear spantree uplinkfast command.
You can disable only spanning tree UplinkFast processing on the switch using the set spantree uplinkfast disable command. This command does not affect the bridge priority, port cost, and port-VLAN cost values on the switch.
This example shows how to disable UplinkFast on the switch and restore the default bridge priority, port cost, and port-VLAN cost values:. Note You must enable BackboneFast on all switches in the network. This feature is supported for use with third-party switches. This example shows how to enable BackboneFast on the switch and verify the configuration:.
This example shows how to disable BackboneFast on the switch and verify the configuration:. Enter the set spantree guard command to enable spanning tree loop guard on a per-port basis. To set all the ports on the switch, use the set spantree mst global-defaults loop-guard command.
To enable loop guard on an individual port, perform this task in privileged mode:. Enter the set spantree guard command to disable spanning tree loop guard on a per-port basis. To disable loop guard on all the ports on a switch, use the set spantree mst global-defaults loop-guard command.
Caution You can use PortFast to connect a single end station or a switch port to a switch port. If you enable PortFast on a port that is connected to another Layer 2 device, such as a switch, you might create network loops. Warning:Connecting Layer 2 devices to a fast start port can cause. Then, if a BPDU is received, the port will be shut down. So if you do plug a switch into a port, it will receive a BPDU on there and this can allow you to switch to automatically shut down that port to prevent a loop from happening.
It is best practise to use these commands on your networks where you've got ports that the end hosts are going to be plugged into.
To do that in global config, we use the command:. Spanning Tree Root Guard prevents an unintended switch from becoming the root bridge. For example, you have an old switch which had been in a different office and it happened to be the root bridge in that different office, but it's a much older switch than the root bridge which is in your main office. It happens to have a higher priority than the current root bridge. Now, that old switch is going to become the root bridge and you want to make sure that this should not happen.
Another reason that the wrong switch could become a root bridge is maybe that you're under an attack. What the attacker will do is put a switch in the network, trying to make that the root bridge to force traffic to come through the switch that they're controlling. They'll then be able to sniff the traffic and gain access to sensitive information. Labels: LAN Switching.
Ganesh Hariharan. Global mode spanning-tree portfast bpduguard default It enables bpduguard on ports that have port-fast configuration, puts port in errdisable upon receiving a bpdu. Global mode spanning-tree portfast bpdufilter default It enables bpdufiltering on ports that have port-fast configuration, so it sends a few bpdu while enabling port then it filters bdpu unless receives a bpdu, after that it changes from port-fast mode and disables filtering for port to operate like a normal port because it has received bpdu.
Tags: authentication. Mohamed Sobair. Rising star. HTH Mohamed. I would stay clear from it personally. Community Member. I can answer that one ayokunies. Karthikeyan Ravichandran. Regards, Dave. Naveen Gurjar. Shaun Whitehorse. It seems that you already have it configured correctly. Latest Contents. Created by Zydain on PM. Created by hmc on AM. Just those 2 switches. Created by RB on AM. When the link on a bridge port goes up, STP calculation occurs on that port.
The result of the calculation is the transition of the port into forwarding or blocking state. The result depends on the position of the port in the network and the STP parameters.
This calculation and transition period usually takes about 30 to 50 seconds. At that time, no user data pass via the port. Some user applications can time out during the period.
In order to allow immediate transition of the port into forwarding state, enable the STP PortFast feature. PortFast immediately transitions the port into STP forwarding mode upon linkup.
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