Chapter 7 Configuring STP and RSTP on the ML-Series Card

STP Features

STP Overview

STP is a Layer 2 link management protocol that provides path redundancy while preventing loops in the network. For a Layer 2 Ethernet network to function properly, only one active path can exist between any two stations. Spanning-tree operation is transparent to end stations, which cannot detect whether they are connected to a single LAN segment or a switched LAN of multiple segments.

When you create fault-tolerant internetworks, you must have a loop-free path between all nodes in a network. The spanning-tree algorithm calculates the best loop-free path throughout a switched Layer 2 network. Switches send and receive spanning-tree frames, called bridge protocol data units (BPDUs), at regular intervals. The switches do not forward these frames, but use the frames to construct a loop-free path.

Multiple active paths among end stations cause loops in the network. If a loop exists in the network, end stations might receive duplicate messages. Switches might also learn end-station MAC addresses on multiple Layer 2 interfaces. These conditions result in an unstable network.

Spanning tree defines a tree with a root switch and a loop-free path from the root to all switches in the Layer 2 network. Spanning tree forces redundant data paths into a standby (blocked) state. If a network segment in the spanning tree fails and a redundant path exists, the spanning-tree algorithm recalculates the spanning-tree topology and activates the standby path.

When two interfaces on a switch are part of a loop, the spanning-tree port priority and path cost settings determine which interface is put in the forwarding state and which is put in the blocking state. The port priority value represents the location of an interface in the network topology and how well it is located to pass traffic. The path cost value represents media speed.

Supported STP Instances

The ML-Series card supports the per-VLAN spanning tree (PVST+) and a maximum of 255 spanning-tree instances.

Caution At more than 100 STP instances the STP instances may flap and may result in MAC entries flushed, and MAC entries learned again and again. This will cause flooding in the network. So it is recommended to keep the STP instances to be less than 100, to keep system from being unstable.

Bridge Protocol Data Units

The stable, active, spanning-tree topology of a switched network is determined by these elements:

•Unique bridge ID (switch priority and MAC address) associated with each VLAN on each switch

•Spanning-tree path cost to the root switch

•Port identifier (port priority and MAC address) associated with each Layer 2 interface

When the switches in a network are powered up, each functions as the root switch. Each switch sends a configuration BPDU through all of its ports. The BPDUs communicate and compute the spanning-tree topology. Each configuration BPDU contains this information:

•Unique bridge ID of the switch that the sending switch identifies as the root switch

•Spanning-tree path cost to the root

•Bridge ID of the sending switch

Cisco ONS 15310-CL, ONS 15310-MA, and ONS 15310-MA SDH Ethernet Card Software Feature and Configuration Guide, R9.1 and R9.2

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Cisco Systems ONS 15310-MA, ONS 15310-CL manual STP Overview, Supported STP Instances, Bridge Protocol Data Units
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ONS 15310-CL, ONS 15310-MA, Cisco ONS 15310-MA specifications

Cisco Systems has long been a leader in networking and telecommunications technology, and among its impressive lineup of products, the Cisco ONS 15310 series stands out as an essential solution for optical networking. This series includes models such as the ONS 15310-MA, ONS 15310-CL, and ONS 15310-CA, each designed to meet the diverse needs of service providers and enterprises seeking to enhance their optical transport networks.

The Cisco ONS 15310-MA is an advanced multi-service platform designed for metropolitan area networks. It facilitates the seamless transport of data, voice, and video over optical networks. One of its main features is its ability to support a variety of interfaces, including Ethernet, SONET/SDH, and Wavelength Division Multiplexing (WDM), allowing users to integrate multiple services into a single platform. Additionally, the ONS 15310-MA supports advanced traffic management and Quality of Service (QoS) features to prioritize critical applications and ensure consistent performance.

The ONS 15310-CL variant is tailored for more specific applications, providing enhanced capabilities aimed at delivering carrier-grade services. It features a robust architecture that accommodates high-capacity traffic without compromising reliability. This model emphasizes low power consumption and a compact design, making it suitable for deployment in space-constrained environments. The ONS 15310-CL also supports a wide range of optical interfaces, making it highly flexible for various network configurations.

In terms of technologies, the Cisco ONS 15310 series leverages Optical Transport Network (OTN) capabilities, providing high efficiency and greater bandwidth utilization. OTN technology enables efficient error correction and adds resilience to the network through its built-in protection mechanisms. Furthermore, the series supports seamless integration with existing IP/MPLS networks, creating a cohesive infrastructure as organizations evolve their networking requirements.

One of the defining characteristics of the ONS 15310 series is its focus on scalability. Network operators can start with a modest deployment and gradually expand capacity as demand grows. This adaptability is complemented by Cisco's comprehensive management and monitoring tools, providing operators with real-time insights into network performance and facilitating proactive management.

In conclusion, the Cisco ONS 15310-MA and ONS 15310-CL models represent sophisticated solutions for modern optical networks. With their versatile features, advanced technologies, and robust design, they empower service providers and enterprises to build resilient, high-capacity networks that meet the demands of today’s data-driven world.
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