Moxa Technologies PT-7728 user manual Using STP on a Network with Multiple VLANs

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PT-7728 User’s Manual

Featured Functions

yBridge A has been selected as the Root Bridge, since it was determined to have the lowest Bridge Identifier on the network.

ySince Bridge A is the Root Bridge, it is also the Designated Bridge for LAN segment 1. Port 1 on Bridge A is selected as the Designated Bridge Port for LAN Segment 1.

yPorts 1 of Bridges B, C, X, and Y are all Root Ports sine they are nearest to the Root Bridge, and therefore have the most efficient path.

yBridges B and X offer the same Root Path Cost for LAN segment 2. However, Bridge B was selected as the Designated Bridge for that segment since it has a lower Bridge Identifier. Port 2 on Bridge B is selected as the Designated Bridge Port for LAN Segment 2.

yBridge C is the Designated Bridge for LAN segment 3, because it has the lowest Root Path Cost for LAN Segment 3:

yThe route through Bridges C and B costs 200 (C to B=100, B to A=100)

yThe route through Bridges Y and B costs 300 (Y to B=200, B to A=100)

yThe Designated Bridge Port for LAN Segment 3 is Port 2 on Bridge C.

Using STP on a Network with Multiple VLANs

IEEE Std 802.1D, 1998 Edition, does not take into account VLANs when calculating STP information—the calculations only depend on the physical connections. Consequently, some network configurations will result in VLANs being subdivided into a number of isolated sections by the STP system. You must ensure that every VLAN configuration on your network takes into account the expected STP topology and alternative topologies that may result from link failures.

The following figure shows an example of a network that contains VLANs 1 and 2. The VLANs are connected using the 802.1Q-tagged link between Switch B and Switch C. By default, this link has a port cost of 100 and is automatically blocked because the other Switch-to-Switch connections have a port cost of 36 (18+18). This means that both VLANs are now subdivided—VLAN 1 on Switch units A and B cannot communicate with VLAN 1 on Switch C, and VLAN 2 on Switch units A and C cannot communicate with VLAN 2 on Switch B.

100BaseTX full-duplex Link; only carries VLAN1 (path cost =18)

Block

100BaseTX full-duplex Link; only carries VLAN2 (path cost =18)

802.1Q tagged, 10BaseTx half-duplex Link camies VLAN1, 2 (path cost = 100)

To avoid subdividing VLANs, all inter-switch connections should be made members of all available 802.1Q VLANs. This will ensure connectivity at all times. For example, the connections between Switches A and B, and between Switches A and C should be 802.1Q tagged and carrying VLANs 1 and 2 to ensure connectivity.

See the Configuring Virtual LANs section for more information about VLAN Tagging.

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Contents First Edition, February Moxa Inc Moxa PowerTrans Switch PT-7728 User’s ManualCopyright Notice TrademarksDisclaimer Table of Contents Appendix a MIB Groups Appendix B Specifications Introduction ‰ Overview ‰ Package Checklist ‰ Software FeaturesPackage Checklist Software FeaturesOverview Getting Started Serial Console Configuration 115200, None, 8, 1, VT100 PT-7728 User’s Manual Getting Started Key Function Configuration by Telnet ConsolePT-7728 User’s Manual Getting Started PT-7728 User’s Manual Getting Started Configuration by Web Browser Disabling Telnet and Browser Access Featured Functions System Identification Configuring Basic SettingsPassword PasswordAccount Grant access to one host with a specific IP address Accessible IPGrant access to any host on a specific subnetwork Hosts That Need Access Input FormatPort EnableDescription NameNetwork SpeedFDX Flow Ctrl Switch IP Address Auto IP ConfigurationSwitch Subnet Mask Default GatewayDaylight Saving Time TimeCurrent Time Current DateSystem File Update-By Remote Tftp Tftp Server IP/Name Configuration Files Path and NameFirmware Files Path and Name Log Files Path and NameFactory Default System File Update-By Local Import/ExportPort Trunking Concept Using Port TrunkingTrunk Group Maximum of 4 trunk groups Configuring Port TrunkingTrunk Type Available Ports/Member PortsConfiguring Snmp Setting DescriptionTrunk Table Snmp Versions Snmp Read/Write SettingsV1, V2c Read Community V1, V2c Write/Read Community1st Trap Server IP/Name Setting Description Factory Default Setting Description Factory DefaultPrivate MIB information Using Communication RedundancyTurbo Ring Concept Initial setup for Turbo Ring or Turbo RingTurbo Ring with odd number switches Determining the Redundant Path for Turbo Ring Ring Coupling ConfigurationSwitch B Configuring Turbo Ring and Turbo Ring Dual-Homing Configuration for Turbo RingConfiguring Turbo Ring Master/Slave Now ActiveRedundancy Protocol Set as MasterEnable Ring Coupling Coupling PortCoupling Control Port Ring 1/2-Status Enable RingRing 1/2-1st Ring Port Status Ring 1/2-2nd Ring Port Status Coupling-ModePrimary/Backup Port Coupling ModeSTP/RSTP Concept What is STP?PT-7728 User’s Manual Featured Functions How STP Works STP ConfigurationSTP Requirements Port Speed Path Cost 802.1D Edition 802.1w-2001STP Reconfiguration Differences between Rstp and STPSTP Example Using STP on a Network with Multiple VLANs Root/Not Root Configuring STP/RSTPProtocol of Redundancy Bridge PriorityEnable STP per Port Forwarding DelayHello Time sec Max. Age secConfiguration Limits of RSTP/STP Using Traffic PrioritizationWhat is Traffic Prioritization? Traffic Prioritization ConceptIeee 802.1p Priority Level Ieee 802.1D Traffic Type How Traffic Prioritization WorksDifferentiated Services DiffServ Traffic Marking Traffic PrioritizationTraffic Queues QoS Classification Configuring Traffic PrioritizationQueuing Mechanism Inspect TOSCoS Mapping Setting Description FactoryTOS/DiffServ Mapping Inspect COSUsing Virtual LAN What is a VLAN?Virtual LAN Vlan Concept Benefits of VLANs VLANs and the PowerTransManaging a Vlan Communication Between VLANsVLANs Tagged and Untagged Membership Sample Applications of VLANs using PT-7728PT-7728 User’s Manual Featured Functions Vlan Settings Configuring Virtual LANManagement Vlan ID Port TypeWhat is an IP Multicast? Using Multicast FilteringConcept of Multicast Filtering Vlan TableBenefits of Multicast Multicast FilteringNetwork without multicast filtering Igmp Internet Group Management Protocol Snooping Mode Multicast Filtering and Moxa PowerTrans SwitchQuery Mode Network with multicast filteringIgmp Multicast Filtering Configuring Igmp SnoopingGmrp Garp Multicast Registration Protocol Static Multicast MACIgmp Snooping Settings Add Static Multicast MAC Configuring Gmrp Using Bandwidth ManagementGmrp enable Gmrp TableConfiguring Bandwidth Management Broadcast Storm Protection Traffic Rate Limiting SettingsIngress Configuring Static Port Lock Using Port Access ControlStatic Port Lock IeeeDatabase Option Configuring IeeeRadius Server Server PortLocal User Database Setup 802.1X Re-AuthenticationUsing Auto Warning Port Access Control TableLocal User Database Setup Event Type Configuring Email WarningMoxaPowerTransSwitch0001@SwitchLocation Email SetupPort Events Mail Server IP/NamePassword Setting Configuring Relay WarningAccount Name Email AddressEvent Setup Using Set Device IP Using Line-Swap-Fast-RecoveryConfiguring Line-Swap Fast Recovery Override relay alarm settingsSet up the connected devices Configuring Set Device IPMirror Port Using DiagnosisUsing Monitor Monitor by SwitchPing Monitor by Port Using the MAC Address TableMAC Using Event LogSyslog Server Using SyslogPT-7728 User’s Manual Featured Functions MIB II.2 Interfaces Group MIB II.1 System GroupMIB II.4 IP Group MIB II.5 Icmp GroupMIB II.10 Transmission Group MIB II.11 Snmp GroupMIB II.17 dot1dBridge Group Private Traps Public TrapsSwitch Properties TechnologyInterface Optical Fiber 100BaseFX PowerWarranty MechanicalEnvironmental
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