NEC INTELLIGENT L2 SWITCH N8406-022A Application Manual

Also see for N8406-022A: Reference guide

Contents

NEC INTELLIGENT L2 SWITCH N8406-022A Application Manual Manual pdf 50 page image

Spanning Tree Protocol 50Port path costThe port path cost assigns lower values to high-bandwidth ports, such as Gigabit Ethernet, to encourage their use.The objective is to use the fastest links so that the route with the lowest cost is chosen. A value of 0 indicates thatport cost is computed dynamically based on link speed. This works when forcing link speed, so it does not justapply to “auto negotiated link speed”.By default, all switch ports have the path cost set to 4, independent of the link speed. To use dynamic path cost,based on link speed, set the path cost to 0 (zero). For example, if the path cost is set to zero:• A 100 Mbps link receives a path cost of 19• A 10 Mbps link receives a path cost of 100Spanning Tree Group configuration guidelinesThis section provides important information on configuring Spanning Tree Groups (STGs).Default Spanning Tree configurationIn the default configuration, a single STG with the ID of 1 includes all ports except Port 19 on the switch. It is calledthe default STG. All other STGs (except the default STG) are empty, and VLANs must be added by the user.You cannot assign ports directly to an STG. Add the ports to a VLAN, and add the VLAN to the STG. STGs 1-31are enabled by default and assigned an ID number from 1 to 31. STG 32 is disabled by default, and contains themanagement VLAN 4095.An STG cannot be deleted, only disabled. If you disable the STG while it still contains VLAN members, SpanningTree will be off on all ports belonging to that VLAN.Adding a VLAN to a Spanning Tree GroupIf no VLANs exist beyond the default VLAN 1, see the “Creating a VLAN” section in this chapter for information onadding ports to VLANs.Add the VLAN to the STG using the command /cfg/l2/stp /add .Creating a VLANWhen you create a VLAN, then that VLAN automatically belongs to STG 1, the default STG. If you want the VLANin another STG, you must move the VLAN by assigning it to another STG.To move a newly created VLAN to an existing STG:1. Create the VLAN.2. Add the VLAN to an existing STG.When creating a VLAN also consider the following:• A VLAN cannot belong to more than one STG.• VLANs that span multiple switches must be mapped within the same Spanning Tree Group (have the sameSTG ID) across all the switches.Rules for VLAN tagged portsRules for VLAN tagged ports are listed below:• If a port is tagged, it can belong to multiple STGs.• When a tagged port belongs to more than one STG, the egress BPDUs are tagged to distinguish the BPDUsof one STG from those of another STG.• An untagged port cannot span multiple STGs.