Difference between revisions of "CCNA Explorer 3 STP"

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===STP Port States and BPDU Timers===
 
===STP Port States and BPDU Timers===
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Port States:
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;Blocking: The port is a non-designated port and does not participate in frame forwarding. The port receives BPDU frames to determine the location and root ID of the root bridge switch and what port roles each switch port should assume in the final active STP topology.
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;Listening: STP has determined that the port can participate in frame forwarding according to the BPDU frames that the switch has received thus far. At this point, the switch port is not only receiving BPDU frames, it is also transmitting its own BPDU frames and informing adjacent switches that the switch port is preparing to participate in the active topology.
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;Learning: The port prepares to participate in frame forwarding and begins to populate the MAC address table.
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;Forwarding: The port is considered part of the active topology and forwards frames and also sends and receives BPDU frames.
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;Disabled: The Layer 2 port does not participate in spanning tree and does not forward frames. The disabled state is set when the switch port is administratively disabled.
 
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|[[Image:ScreenShot179.jpg|800px|left|thumb|Verify portfast]]
 
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==STP Convergence==
 
==STP Convergence==
 
===STP Convergence===
 
===STP Convergence===

Revision as of 00:03, 13 January 2012

STP

Redundant Layer 2 Topologies

Redundancy

Simple network VLAN mangement
Starting point
Path Failure - Access to Distribution
Path Failure - Distribution to Core
Switch Failure - Distribution layer
Switch Failure - Core layer

Issues with Redundancy

Layer 2 Loops
Broadcast loops

Real-world Redundancy Issues

Non-Redundant network topology
Loops from 2 connections in the same switch
Loops from connections to a second switch
Loops int the cubicles

Introduction to STP

The Spanning Tree Algorithm

STP Topology
STP Redundancy
STP Port names

Root ports - Switch ports closest to the root bridge.
Designated ports - All non-root ports that are still permitted to forward traffic on the network.
Non-designated ports - All ports configured to be in a blocking state to prevent loops.

Root Bridge
BID fields
Port cost
Configuring port costs
Path Cost
Verify port and path costs

STP BPDU

BPDU Fields

Version - The version field indicates the version of the protocol, This field contains the value zero.
Message type - The message type field indicated the type of message, this field contains the value zero.
Flags - The flags field includes one of the following: Topology change(TC) bit, which signals a topology change in the event a path to the root bridge has been disrupted. Topology change acknowledgment(TCA) bit, which is set to acknowledge receipt of a configuration messege with the TC bit set.
Root ID - The Root ID field indicates the root bridge by listing its 2-byte prority followed by its 6-byte MAC address ID.
Bridge ID - The Bridge ID field indicates the priority and MAC address ID of the bridge sending the message
Port ID - The Port ID field indicates the port number from which the configuration message was sent.
Forward Delay - The Forward delay field indicates the length of time that bridges should wait before transitioning to a new state after topology change.

BPDU Fields
BPDU Process Step 1
BPDU Process Step 2
BPDU Process Step 3
BPDU Process Step 4
BPDU Process Step 5
BPDU Process Step 6
BPDU Process Step 7
BPDU Process Step 8
BPDU Process Step 9

Bridge ID

BID Fields
Priority-based desicions
MAC Address-based desicions
Configure STP
Verify STP

Port Roles

Root Port
The root port exists on non-root bridges and is the switch port with the best path to the root bridge.
Designated Port
The designated port exists on root and non-root bridges. For root bridges, all switch ports are designated ports. Only one designated port is allowed per segment. Designated ports are capable of populating the MAC table.
Non-designated Port
The non-designated port is a switch port that is blocked, so it is not forwarding data frames and not populating the MAC address table with source addresses.
Disabled Port
The disabled port is a switch port that is administratively shut down.
STP Port Roles
STP Port Roles
Configure port priority
Verify Port Roles and Priority

STP Port States and BPDU Timers

Port States:

Blocking
The port is a non-designated port and does not participate in frame forwarding. The port receives BPDU frames to determine the location and root ID of the root bridge switch and what port roles each switch port should assume in the final active STP topology.
Listening
STP has determined that the port can participate in frame forwarding according to the BPDU frames that the switch has received thus far. At this point, the switch port is not only receiving BPDU frames, it is also transmitting its own BPDU frames and informing adjacent switches that the switch port is preparing to participate in the active topology.
Learning
The port prepares to participate in frame forwarding and begins to populate the MAC address table.
Forwarding
The port is considered part of the active topology and forwards frames and also sends and receives BPDU frames.
Disabled
The Layer 2 port does not participate in spanning tree and does not forward frames. The disabled state is set when the switch port is administratively disabled.
STP Port States
BPDU Timers
BPDU Roles and Timers
Configure network diameter
Cisco Portfast technology
Configure portfast
Verify portfast

STP Convergence

STP Convergence

STP Convergence

Step 1. Electing A Root Bridge

Electing a root bridge

Step 2. Elect Root Ports

Elect a root port step 1
Elect a root port step 2
Elect a root port step 3
Elect a root port step 4

Step 3. Electing Desgnated Ports and Non-Designated Ports

Elect port step 1
Elect port step 2
Elect port step 3
Elect port step 4
Elect port step 5
Elect port step 6
Elect port step 7

STP Topology Change

STP Topology Change
Topology change notification(TCN) messages are flooded out the root port, until it reaches the root bridge.
STP Broadcast notification
The Root Bridge broadcasts Topology change messages

PVST+, RSTP and Rapid-PVST+

Cisco and STP Variants

STP Variants

PVST+

PVST+
PVST+ Bridge ID
PVST+ Bridge ID example
Default PVST+ configuration
Configure PVST+
Configure PVST+
Configure PVST+ Priority
Verify PVST+

RSTP

RSTP
Characteristics of RSTP
RSTP BPDU

Edge Ports

Edge Ports

Link Types

Link Types

Point-to-point Link Type - Links attaches to switch ports that are operating in full-duplex mode
Shared Link Type - This link is attached to a port that is operating in half-duplex mode

RSTP Port States and Port Roles

RSTP Port States
RSTP Port States
RSTP Port States
RSTP Port Roles

Configure Rapid-PVST+

Rapid-PVST+ Topology
Rapid-PVST+ Example configuration
Rapid-PVST+ verification

Design STP for Trouble Avoidance

Know where the root is
Manual Pruning
Layer 3 Switching
Layer 3 Switching

Troubleshoot STP Operation

Troubleshoot a failure
PortFast configuration error
Network diameter issues

Chapter Summary

Chapter summary
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