Radware Alteon User Manual

Document ID: RDWR-ALOS-V2900_AG1302 99
Chapter 7 – Spanning Tree Protocol
When multiple paths exist on a network, the Spanning Tree Protocol (STP) configures the network so
that Alteon uses only the most efficient path.
The following topics are addressed in this chapter:
• Overview, page 99
• Bridge Protocol Data Units (BPDUs), page 99
• Spanning Tree Group Configuration Guidelines, page 100
• Multiple Spanning Trees, page 102
• Rapid Spanning Tree Protocol, page 105
• Multiple Spanning Tree Protocol, page 107
Overview
STP detects and eliminates logical loops in a bridged or switched network. STP forces redundant
data paths into a standby (blocked) state. When multiple paths exist, STP configures the network so
that an Alteon uses only the most efficient path. If that path fails, STP sets up another active path
on the network to sustain network operations.
The relationship between port, trunk groups, VLANs, and spanning trees is described in Table 11:
Note: Due to STP’s sequence of listening, learning, and forwarding or blocking, lengthy delays may
occur. For more information on using STP in cross-redundant topologies, see Eliminating Loops with
STP and VLANs, page 568.
Bridge Protocol Data Units (BPDUs)
To create a spanning tree, Alteon generates a configuration Bridge Protocol Data Unit (BPDU), which
it then forwards out of its ports. All devices in the Layer 2 network participating in the spanning tree
gather information about other devices in the network through an exchange of BPDUs.
A BPDU is a 64-byte packet that is sent out at a configurable interval, which is typically set at 2
seconds. The BPDU is used to establish a path, much like a "hello" packet in IP routing. BPDUs
contain information about the transmitting bridge and its ports, including bridge and MAC addresses,
bridge priority, port priority, and path cost. If the ports are tagged, each port sends out a special
BPDU containing the tagged information.
Table 11: Relationship Between Port, Trunk Groups, VLANs, and Spanning Trees
Alteon Element Belongs to
Port Trunk group or one or more VLANs
Trunk group One or more VLANs
VLAN One STP group

Radware Alteon Specifications

General

Model	Alteon
Manufacturer	Radware
Layer	Layer 4-7
Type	Application Delivery Controller (ADC)
Features	Load balancing, SSL offloading, application acceleration, DDoS protection
Form Factor	Virtual Appliance