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Spanning Tree Protocol - Computer Network - Lecture Slides, Slides of Computer Networks

Chhattisgarh Swami Vivekanand Technical University Computer Networks

Spanning Tree Protocol, Redundancy, Redundant Topologies, Redundantly Switched Networks, Broadcast Storms, STP Process, Selecting the Root Bridge, Spanning Tree Port States and many other topics of Computer Network can be find in my documents.

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Spanning Tree Protocol

Semester 3 – Module 7

Students completing this module should be able to:

Define redundancy and its importance in networking

Describe the key elements of a redundant networking topology

Define broadcast storms and describe their impact on switched networks

Define multiple frame transmissions and describe their impact on switched networks

Identify causes and results of MAC address database instability

Identify the benefits and risks of a redundant topology

Describe the role of spanning tree in a redundant-path switched network

Identify the key elements of spanning tree operation

Describe the process for root bridge election

List the spanning-tree states in order

Compare Spanning-Tree Protocol and Rapid Spanning-Tree Protocol

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Spanning Tree Protocol

Semester 3 – Module 7

Students completing this module should be able to:

Define redundancy and its importance in networking Describe the key elements of a redundant networking topology Define broadcast storms and describe their impact on switched networks Define multiple frame transmissions and describe their impact on switched networks Identify causes and results of MAC address database instability Identify the benefits and risks of a redundant topology Describe the role of spanning tree in a redundant-path switched network Identify the key elements of spanning tree operation Describe the process for root bridge election List the spanning-tree states in order Compare Spanning-Tree Protocol and Rapid Spanning-Tree Protocol Docsity.com

Overview

Redundancy in a network is extremely important

because:

Provides fault tolerance
protect against network downtime due to a single point of failure
Network engineers are often required to make

difficult decisions, balancing the cost of

redundancy with the need for network availability

The Spanning-Tree Protocol is used in switched

networks to create a loop free logical topology

from a physical topology that has loops

Redundant Topologies

• A goal of redundant topologies is to

eliminate network outages caused by a

single point of failure

• All networks need redundancy for

enhanced reliability

• Switches can be used for creating

Redundantly Switched Networks

Downfalls:
- Broadcast storms
- Multiple frame copies
- MAC address table instability problems

Broadcast Storms

• No Time To Live (TTL) in frames, so

switches send and resend the same

broadcast/mulitcast over and over until one

of the switches is disconnected

• Multicasts are treated as broadcasts by the

switches

• Broadcasts and multicasts frames are

flooded out all ports, except the one on

which the frame was received

STP – The Process

Select a Route Bridge
- Based on BID sent from each Bridge, containing a Bridge Priority and the Base Switch MAC address
- Lowest Priority is designated as ROOT
Select a Route Port on all NON-Route Bridges
- Best path to Root Bridge
Select one Designated Port per segment
- Forwarding Ports that are part of the Spanning-tree
Select Non-designated ports
- Placed in Blocking mode

Spanning-Tree Protocol - BPDUs

BPDUs – messages sent by a switch to allow information to be shared to create a loop free logical topology
BPDUs are sent every two seconds by default
BPDUs are sent when changes occur in the network to the Root Bridge to be distributed to all Bridges in the Spanning- tree
BPDUs contain enough information so that all switches can do the following: - Select a single switch that will act as the root of the spanning tree - Calculate the shortest path from itself to the root switch - Designate one of the switches as the closest one to the root, for each LAN segment. This bridge is called the “designated switch”. The designated switch handles all communication from that LAN towards the root bridge - Choose one of its ports as its root port, for each non-root switch. This is the interface that gives the best path to the root switch - Select ports that are part of the spanning tree, the designated ports. Non- designated ports are blocked

Spanning-Tree Port States

NOTE: Total time for a port to go from Blocking to Forwarding is 50 seconds! Docsity.com

Spanning Tree Protocol - Computer Network - Lecture Slides, Slides of Computer Networks

Related documents

Partial preview of the text

Download Spanning Tree Protocol - Computer Network - Lecture Slides and more Slides Computer Networks in PDF only on Docsity!

Spanning Tree Protocol

Overview

because:

difficult decisions, balancing the cost of

redundancy with the need for network availability

networks to create a loop free logical topology

from a physical topology that has loops

Redundant Topologies

• A goal of redundant topologies is to

eliminate network outages caused by a

single point of failure

• All networks need redundancy for

enhanced reliability

• Switches can be used for creating

Redundantly Switched Networks

Broadcast Storms

• No Time To Live (TTL) in frames, so

switches send and resend the same

broadcast/mulitcast over and over until one

of the switches is disconnected

• Multicasts are treated as broadcasts by the

switches

• Broadcasts and multicasts frames are

flooded out all ports, except the one on

which the frame was received

STP – The Process

Spanning-Tree Protocol - BPDUs

Spanning-Tree Port States

Spanning-Tree Recalculation

the switch and bridge ports are in either the

forwarding or blocked state

and BPDUs

and bridges recompute the Spanning Tree and

cause a disruption of user traffic

using the IEEE 802.1D standard can take up to

50 seconds

Rapid STP

• Link types have been defined as point-to-

point, edge-type, and shared.

switched network to be learned immediately

• Point-to-point links and edge-type links

can go to the forwarding state immediately

• Network convergence does not need to be

any longer than 15 seconds with these

changes