Port Speed Link Type Path Cost 802.1D-1998 802.1w | 3Com 3 specification

How STP Works 37

cost, the less efficient the link. Table 3 shows the default port costs for a Switch.

Table 3 Default port costs

Port Speed	Link Type	Path Cost	Path Cost
Port Speed	Link Type	802.1D-1998	802.1w

10 Mbps	Half Duplex	100	2,000,000
	Full Duplex	95	1,999,999
	Aggregated Link	90	1,000,000*
100 Mbps	Half Duplex	19	200,000
	Full Duplex	18	199,999
	Aggregated Link	15	100,000*
1000 Mbps	Full Duplex	4	20,000
	Aggregated Link	3	10,000*

*This path cost is correct where there are two ports in an aggregated link. However, if there are more ports in the aggregated link, the path cost will be proportionately lower. For example, if there are four ports in the aggregated link, the 802.1w path costs will be: 500,000 for

10 Mbps, 50,000 for 100 Mbps, and 5,000 for 1000 Mbps. The 802.1D-1998 path cost values are not affected by the number of ports in an aggregated link.

STP Calculation The first stage in the STP process is the calculation stage. During this stage, each bridge on the network transmits BPDUs that allow the system to work out:

■The identity of the bridge that is to be the Root Bridge. The Root Bridge is the central reference point from which the network is configured.

■The Root Path Costs for each bridge — that is, the cost of the paths from each bridge to the Root Bridge.

■The identity of the port on each bridge that is to be the Root Port. The Root Port is the one that is connected to the Root Bridge using the most efficient path, that is, the one that has the lowest Root Path Cost. Note that the Root Bridge does not have a Root Port.

■The identity of the bridge that is to be the Designated Bridge of each LAN segment. The Designated Bridge is the one that has the lowest Root Path Cost from that segment. Note that if several bridges have the same Root Path Cost, the one with the lowest Bridge Identifier becomes the Designated Bridge.

All traffic destined to pass in the direction of the Root Bridge flows through the Designated Bridge. The port on this bridge that connects to the segment is called the Designated Bridge Port.

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3Com 3 manual Port Speed Link Type Path Cost 802.1D-1998 802.1w

Contents

SuperStack 3Com Corporation 5400 Bayfront Plaza Santa Clara, California Contents Using Multicast Filtering Status Monitoring and Statistics IP Addressing About this Guide List conventions that are used throughout this guide Conventions Documentation RelatedComments Pddtechpubscomments@3com.com Registration Product Switch Features Page Switch Features What isManagement Software? Switch Features Overview For more information about multicast filtering, see Using Ports operating at 1000 Mbps only support full duplex modeDuplex Flow Control Resilience Features For more information about STP and RSTP, see Using For more information about Quality of Service, see Using Quality of ServiceEvent Notification For more information about VLANs, see Setting Up Virtual Port Features Ports operating at 1000 Mbps support full duplex mode only Port Features Switch units connected using an aggregated link Aggregated Links Traffic Distribution and Link Failure on Aggregated Links 2 Gbps aggregated link between two Switch units Optimizing Bandwidth Relevant multicast group Using Multicast Filtering Using Multicast Filtering Snooping Mode Query modeQuery Mode That support IP Igmp v2 protocolIgmp multicast filtering works as follows Enabling Igmp Multicast Learning Igmp Multicast Filtering Using Multicast Filtering Protocol STP Spanning TreeNetwork Ieee 802.1w standard What is STP? Traffic flowing through Bridge B Port Speed Link Type Path Cost 802.1D-1998 802.1w Using Resilience Features Port costs in a network Configuration 2 Redundancy through Meshed Backbone Configuration 1 Redundancy for Backbone LinkConfiguration 3 Redundancy for Cabling Error STP configurations Using STP on a Default BehaviorNetwork with Multiple VLANs Configuration that separates VLANs Using Resilience Features How Switch What is the SwitchDatabase? Database Entries Databases entries can have three states Switch Database Entry States Prioritization? What is TrafficAvailable Converged network applications Used by organizations with a 802.1D Priority Levels How Traffic Prioritization Works Traffic Prioritization Your Switch Configuring traffic prioritization for QoS on a Switch How traffic is processed to provide Quality of Service Using Traffic Prioritization Network efficiency and reduce the load on your network What is RMON?That allows you to monitor the traffic of LANs or VLANs Events AlarmsIt improves your efficiency Rmon Switch Low Threshold Statistic High Threshold Recovery Period Low Threshold Statistic High Threshold Recovery Status Monitoring and Statistics Hardware Status Monitoring Example device summary web Setting UP Virtual Lans VLANs provide extra security VLANs ease the movement of devices on networks VLANs help to control traffic Creating an Ieee 802.1Q Tagged Link Membership Two Vlans connected via a router Using Untagged ConfigurationConfigure the VLANs Examples Add endstation ports on Switch 1 to the VLANs Configure the VLANs on SwitchAdd ports to the VLANs Add endstation ports on Switch 2 to the VLANs Add port 12 on Switch 1 to the VLANsAdd port 11 on Switch 2 to the VLANs Check the Vlan membership for both switches Configuration Obtains IP How Your SwitchInformation How Automatic IP How Automatic IP Configuration Works That a Switch may change its IP address whilst in use Automatic IP configuration featureConsiderations IP Addressing Configuration RulesGlossary IndexPage Configuration Rules for Gigabit Ethernet Configuration Rules Fast Ethernet configuration rules Configuration Rules for Fast Ethernet Appendix a Configuration Rules This chapter contains the following sections Network Simple Network Segments are connected to the Switch which is positionedFamily and 4900 family can be used in your network Example Dual Speed Hub Switch Improving Advanced NetworkResilience of Your Network Performance EnhancingTherefore the overall network performance Simple Overview IP Addresses IP Address Obtaining a Registered IP Address Decimal value of an octet whose bits are all 1s is Dotted Decimal NotationNetwork Portion Subnet mask Extending the Network Prefix Subnet Mask Numbering Or leave the field blank Glossary Glossary Ethernet EndstationEthernet address Fast Ethernet Half duplex GatewayHub Ieee 802.1D Line speed See baud Glossary Rstp See Rapid Spanning Tree Protocol STP See Spanning Tree Protocol STP Page Glossary Numbers Index Igmp multicast filtering 30 Internet Addresses 85 InterNIC Sub-networks. See subnets Switch Database