Spanning Tree Spanning Tree ProtocolProtocolImplementing Cisco Networks

OutlineOutline

IntroductionWhy Use STP?Spanning Tree TermsSpanning Tree Operation

(STA)STP Port StatesSTP TimersSTP Versions

CCNA Project Report 2

IntroductionIntroduction

Layer 2 Bridge-to-Bridge ProtocolLoop Avoidance MechanismDeveloped by Radia PerlmanDefined in IEEE 802.1d standardEnabled by default on Cisco

Catalyst switchesUses the Spanning Tree AlgorithmCreates Loop-free Logical Topology

CCNA Project Report 3

Why Use STP?Why Use STP?

The Need for STPIn a layer 2 switched network, while multiple links betweendevices provide protection against single points of failure,they also introduce physical loops in the network.Redundant links can cause a lot of problems, including:

• Broadcast storms• Multiple copies of Ethernet frame• Thrashing of the MAC table

STP prevents physical networking loops from occurringby identifying the redundant links in the network, and blockingsome of them to create a loop-free logical topology.

CCNA Project Report 4

Spanning Tree TermsSpanning Tree Terms

Root Bridge – the focal point of the network that influences all STP decisions

Root Port – the port (on a nonroot bridge) used to reach the root bridge

Designated Port – the port with the least advertised path cost to the root bridge

CCNA Project Report 5

Spanning Tree Terms Spanning Tree Terms (contd.)(contd.)

Bridge ID – Priority + MAC Address, used to identify each switch in the network, default priority = 32,768

BPDU – Bridge Protocol Data Unit, used by switches to exchange STP information among themselves

Path/Port Cost – determined by the bandwidth of a link

CCNA Project Report 6

Spanning Tree Operation Spanning Tree Operation (STA)(STA)

Step 1: Electing a Root Bridge

• Bridge Priority, Bridge ID, Root Bridge

Step 2: Electing Root Ports

• Path/Port Cost, Root Path Cost, Root Port

Step 3: Electing Designated Ports

• Path/Port Cost, Root Path Cost

CCNA Project Report 8

STP Port StatesSTP Port States

Disabled – Administratively downBlocking – Receives BPDUs onlyListening – Building active

topologyLearning – Building bridging tableForwarding – Building MAC table,

sending/receiving user data

CCNA Project Report 9

STP TimersSTP Timers

Hello Time – how often BPDUs are sent (default = 2 seconds)

Max Age – maximum time to retain the received BPDU information (default = 20 seconds)

Forward Delay – time to wait before transitioning from listening to learning state, and from learning to forwarding state (default = 15 seconds)

CCNA Project Report 10

STP VersionsSTP Versions

Spanning Tree Protocol (IEEE 802.1d)

Per VLAN Spanning Tree (PVST+)Rapid Spanning Tree Protocol, or

RSTP (IEEE 802.1w)

CCNA Project Report 11

Thank YouThank You

Presented by:Premdeep S. GillRoll# LU-0453-10

Batch# 100223

CCNA Project Report 12