PortFast and BPDU Guard for Spanning Tree
The PortFast and BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard features enhance network reliability, manageability, and security for Layer-2 STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. .
Some devices and local stacks running on systems or workstations are capable of generating potential STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. BPDUs that cause DOS attacks. PortFast and BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard features provide stability and security for network topologies to prevent such attacks, and can be applied either independently or together.
The following sections describe:
PortFast
The PortFast feature is introduced to avoid network connectivity issues. These issues are caused by delays in STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. enabled ports moving from blocking-state to forwarding-state after transitioning from the listening and learning states. STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. enabled ports that are connected to devices such as a single switch, workstation, or a server can access the network only after passing all these STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. states. Some applications need to connect to the network immediately, else they will timeout.
Enabling the PortFast feature causes a switch or a trunk port to enter the STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. forwarding-state immediately or upon a linkup event, thus bypassing the listening and learning states. The PortFast feature is enabled at a port level, and this port can either be a physical or a logical port. When PortFast feature is enabled on a switch or a trunk port, the port immediately transitions to the STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. forwarding state.
Though PortFast is enabled the port still participates in STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks.. If the port happens to be part of topology that could form a loop, the port eventually transitions into STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. blocking mode. PortFast is usually configured on an edge port, which means the port should not receive any STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. BPDUs. If the port receives any STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies., it moves back to normal or regular mode and will participate in the listening and learning states.
In most deployments, edge ports are access ports. However, in this scenario there are no restrictions in enabling the PortFast feature. The mode of the port changes from PortFast to non-PortFast when the port receives a STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies.. To re-enable this feature on a port, run the command followed by a command at the interface or port level.
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Configuring PortFast on a non-edge port can cause instability to the STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. topology. |
BPDU Guard
BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard feature protects the port from receiving STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. BPDUs, however the port can transmit STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. BPDUs. When a STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. is received on a BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard enabled port, the port is shutdown and the state of the port changes to (Error-Disable) state. The port remains in the state until the port status is manually changed by using the configuration command followed by a applied on the interface. In most deployments, BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard feature is configured over the PortFast enabled STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. ports, but in this implementation the BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard feature can be enabled on any of the STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. ports, with or without PortFast feature being enabled on these ports.
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It is recommended not to enable the BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard feature on a trunk port that forms the STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. topology. |
Scenarios Supported on PortFast and BPDU Guard
PortFast and BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard features are applied at the port or interface level. These features can also be applied in the following scenarios:
RSTP Rapid Spanning Tree Protocol. RSTP provides significantly faster spanning tree convergence after a topology change, introducing new convergence behaviors and bridge port roles to do this. and PVST Per-VLAN Spanning Tree. PVST provides load balancing of VLANs across multiple ports resulting in optimal usage of network resources. modes
Access and Trunk ports
Physical and Logical ports
In the global RSTP Rapid Spanning Tree Protocol. RSTP provides significantly faster spanning tree convergence after a topology change, introducing new convergence behaviors and bridge port roles to do this. mode, there is only one RSTP Rapid Spanning Tree Protocol. RSTP provides significantly faster spanning tree convergence after a topology change, introducing new convergence behaviors and bridge port roles to do this. instance running in the entire Mobility Master. If the port that is enabled with PortFast and BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard receives any STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies., it affects all ports, as the global RSTP Rapid Spanning Tree Protocol. RSTP provides significantly faster spanning tree convergence after a topology change, introducing new convergence behaviors and bridge port roles to do this. runs on a port basis.
In the PVST Per-VLAN Spanning Tree. PVST provides load balancing of VLANs across multiple ports resulting in optimal usage of network resources. mode, there can be multiple instances of RSTP Rapid Spanning Tree Protocol. RSTP provides significantly faster spanning tree convergence after a topology change, introducing new convergence behaviors and bridge port roles to do this. running, as they are based per VLAN Virtual Local Area Network. In computer networking, a single Layer 2 network may be partitioned to create multiple distinct broadcast domains, which are mutually isolated so that packets can only pass between them through one or more routers; such a domain is referred to as a Virtual Local Area Network, Virtual LAN, or VLAN.. Though it is based per VLAN Virtual Local Area Network. In computer networking, a single Layer 2 network may be partitioned to create multiple distinct broadcast domains, which are mutually isolated so that packets can only pass between them through one or more routers; such a domain is referred to as a Virtual Local Area Network, Virtual LAN, or VLAN., it will still behave in the same way as it does in the global RSTP Rapid Spanning Tree Protocol. RSTP provides significantly faster spanning tree convergence after a topology change, introducing new convergence behaviors and bridge port roles to do this. mode. For example, if there are five VLANs Virtual Local Area Network. In computer networking, a single Layer 2 network may be partitioned to create multiple distinct broadcast domains, which are mutually isolated so that packets can only pass between them through one or more routers; such a domain is referred to as a Virtual Local Area Network, Virtual LAN, or VLAN. and each VLAN Virtual Local Area Network. In computer networking, a single Layer 2 network may be partitioned to create multiple distinct broadcast domains, which are mutually isolated so that packets can only pass between them through one or more routers; such a domain is referred to as a Virtual Local Area Network, Virtual LAN, or VLAN. has a separate RSTP Rapid Spanning Tree Protocol. RSTP provides significantly faster spanning tree convergence after a topology change, introducing new convergence behaviors and bridge port roles to do this. instance running, then any STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. received on any of these five ports effects all ports.
If an STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. is received from any one of the five RSTP Rapid Spanning Tree Protocol. RSTP provides significantly faster spanning tree convergence after a topology change, introducing new convergence behaviors and bridge port roles to do this. instances running, the port that is enabled with BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard shuts down and goes to state. In other words, both PortFast and BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard features are applied on a port basis for both global RSTP Rapid Spanning Tree Protocol. RSTP provides significantly faster spanning tree convergence after a topology change, introducing new convergence behaviors and bridge port roles to do this. and PVST Per-VLAN Spanning Tree. PVST provides load balancing of VLANs across multiple ports resulting in optimal usage of network resources. modes, even though the PVST Per-VLAN Spanning Tree. PVST provides load balancing of VLANs across multiple ports resulting in optimal usage of network resources. runs on a per VLAN Virtual Local Area Network. In computer networking, a single Layer 2 network may be partitioned to create multiple distinct broadcast domains, which are mutually isolated so that packets can only pass between them through one or more routers; such a domain is referred to as a Virtual Local Area Network, Virtual LAN, or VLAN. basis.
Enabling PortFast on a Port
The following procedure enables PortFast on a port:
1. In the node hierarchy, select the device and navigate to .
2. In the table, click the port number for which you want to enable PortFast and BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard.
3. Select the link at the bottom of the tab .
4. Select the check box.
5. Click .
6. Click .
7. In the window, select the check box and click .
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It is recommended to enable PortFast only on access port types. However, PortFast can be enabled on the trunk ports by selecting the check box in the WebUI. |
Execute the following commands to enable PortFast:
(host) [mynode] (config) #interface gigabitinternet <slot>/<module>/<port>
(host) [mynode] (config-if)#spanning-tree portfast
Execute the following commands to disable PortFast:
(host) [mynode] (config) #interface gigabitinternet <slot>/<module>/<port>
(host) [mynode] (config-if) #no spanning-tree portfast
Execute the following command to enable PortFast on trunk ports:
(host) [mynode] (config) #interface gigabitethernet <slot>/<module>/<port>
(host) [mynode] (config-if)#spanning-tree portfast trunk
Execute the following show command to display the status of the STP Spanning Tree Protocol. STP is a network protocol that builds a logical loop-free topology for Ethernet networks. ports:
(host) [mynode] (config-if) #show spanning-tree interface gigabitethernet <slot>/<module>/<port>
Enabling BPDU Guard on a Port
The following CLI Command-Line Interface. A console interface with a command line shell that allows users to execute text input as commands and convert these commands to appropriate functions. command enables PortFast and BPDU Bridge Protocol Data Unit. A BPDU is a data message transmitted across a local area network to detect loops in network topologies. Guard:
(host) [mynode] (config) #interface gigabitinternet <slot>/<module>/<port>
(host) [mynode] (config-if)#spanning-tree bpduguard
