Cisco ONS 15454 SDH Specifications download pdf (Page 388)

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Cisco ONS 15454 SDH Installation and Operations Guide, R3.3

May 2002

Chapter 9 Ethernet Operation

E Series Spanning Tree (IEEE 802.1D)

STP detects and eliminates network loops. When STP detects multiple paths between any two network

hosts, STP blocks ports until only one path exists between any two network hosts (Figure 9-34). The

single path eliminates possible bridge loops. This is crucial for shared packet rings, which naturally

include a loop.

Figure 9-34 An STP blocked path

To remove loops, STP defines a tree that spans all the switches in an extended network. STP forces

certain redundant data paths into a standby (blocked) state. If one network segment in the STP becomes

unreachable, the spanning-tree algorithm reconfigures the spanning-tree topology and reactivates the

blocked path to reestablish the link. STP operation is transparent to end stations, which do not

discriminate between connections to a single LAN segment or to a switched LAN with multiple

segments. The ONS 15454 SDH supports one STP instance per circuit and a maximum of eight STP

instances per ONS 15454 SDH.

Caution Multiple circuits with spanning tree protection enabled will incur blocking, if the circuits traverse a

common card and use the same VLAN.

9.7.1 E Series Multi-Instance Spanning Tree and VLANs

The ONS 15454 SDH can operate multiple instances of STP to support VLANs in a looped topology.

You can dedicate separate circuits across the SDH ring for different VLAN groups (i.e., one for private

TLS services and one for Internet access). Each circuit runs its own STP to maintain VLAN connectivity

in a multi-ring environment.

Procedure: Enable E Series Spanning Tree on Ethernet Ports

Step 1 Display the CTC card view.

Step 2 Click the Provisioning > Port tabs.

Step 3 In the left-hand column, find the applicable port number and check the Stp Enabled checkbox to enable

STP for that port.

Step 4 Click Apply.

9.7.2 E Series Spanning Tree Parameters

Default spanning tree parameters are appropriate for most situations. Contact the Cisco Technical

Assistance Center (TAC) before you change the default STP parameters. To obtain a directory of toll-free

Cisco TAC telephone numbers for your country, refer to the Cisco ONS 15454 SDH Product Overview

preference section.

43388

Redundant path (blocked)

Primary path (forwarding)

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Cisco ONS 15454 SDH Specifications Page 388