Installation and Getting Started Guide
STP also ensures that the device uses the most efficient path when multiple paths exist between ports. Moreover,
if a selected path fails, STP searches for and then establishes an alternate path to prevent or limit retransmission
STP is disabled by default on routing switches but is enabled by default on switches.
For information about configuring STP, see the "Configuring Spanning Tree Protocol (STP)" chapter in the
Advanced Configuration and Management Guide.
HP provides a set of Layer 2 features that extend the operation of standard STP. These features enable you to
fine tune standard STP and avoid some of its limitations. The STP enhancements include the following features:
Fast Port Span – By default, devices running Fast Port Span perform Spanning Tree Protocol (STP)
convergence in four seconds instead of 30 or more seconds for certain ports connected to end stations.
Fast Uplink Span – Enhances STP by allowing an HP device with redundant uplinks to quickly resume
forwarding, in just four seconds. This feature is similar to Fast Port Span but applies to certain inter-switch
links on HP devices, instead of HP links to end stations.
Single-instance STP – Runs a single spanning tree on all ports in the HP device, even if you have already
configured multiple port-based VLANs on the device.
Per VLAN Spanning Tree+ (PVST+) Compatibility – HP devices that are configured to support a separate
spanning tree in each port-based VLAN can interoperate with Cisco devices that are running Per VLAN
Spanning Tree (PVST) or PVST+, Cisco proprietary STP implementations that support separate spanning
trees in each port-based VLAN.
For more information and configuration procedures, see the "Configuring Spanning Tree Protocol (STP)" chapter
in the Advanced Configuration and Management Guide.
A trunk group is a set of ports that provide a high speed link between two HP devices or between an HP device
and a server. A trunk group can provide a transfer rate of up to 4 Gbps of bi-directional traffic.
In addition to enabling load sharing of traffic, trunk groups provide redundant, alternate paths for traffic. Thus, if a
link in a trunk group fails, the device still uses the other links in the trunk group.
A trunk group can consist of two to four ports, and up to 8 ports on a Chassis device. You can configure up to 64
trunk groups on a Chassis device, and up to four trunk groups on Fixed-port devices.
For configuration information, see "Configuring Trunk Groups" on page 9-34.
Port-Based Virtual LANs (VLANs)
By default, all ports in an HP device belong to a common Layer 2 broadcast domain. When the device sends a
Layer 2 broadcast packet, the packet goes out all active ports. A port-based VLAN (Virtual LAN) is a subset of
ports on an HP device that constitutes a Layer 2 broadcast domain.
Port-based VLANs can reduce the likelihood and severity of broadcast storms by reducing the number of ports
affected by a storm. In addition, for devices such as servers that can cause broadcast storms, you can add static
MAC entries for the devices and assign the static entries to a VLAN.
By default, each port-based VLAN maintains a separate spanning tree. You can override this behavior and
configure the device to use the same spanning tree for all VLAN ports if desired. See the "Configuring Spanning
Tree Protocol (STP)" chapter in the Advanced Configuration and Management Guide.
For VLAN configuration information, see the "Configuring Virtual LANs (VLANs)" chapter in the Advanced
Configuration and Management Guide.
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