Cisco Confidential 25.0 Introduction 5.1 Spanning Tree Concepts 5.2 Varieties of Spanning Tree Protocols 5.3 Spanning Tree Configuration 5.4 First-Hop Redundancy Protocols 5.5 Summary...
Trang 1© 2008 Cisco Systems, Inc All rights reserved Cisco Confidential
Redundancy
Scaling Networks
Trang 2Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 2
5.0 Introduction
5.1 Spanning Tree Concepts
5.2 Varieties of Spanning Tree Protocols
5.3 Spanning Tree Configuration
5.4 First-Hop Redundancy Protocols
5.5 Summary
Trang 3Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 3
Describe the different spanning tree varieties
Describe the different varieties of first hop redundancy protocols
implementations.
Trang 4© 2008 Cisco Systems, Inc All rights reserved Cisco Confidential
Concepts
Trang 5Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 5
Redundancy at OSI Layers 1 and 2
Multiple cabled paths between switches:
Improves the reliability and availability of the network
disruption
Trang 6Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 6
Issues with Layer 1 Redundancy:
MAC Database Instability
Ethernet frames do not have a time to live (TTL) attribute
until a link is disrupted and breaks the loop
If there is more than one path for the frame to be forwarded out, an
endless loop can result
on a switch to constantly change with the updates from the broadcast frames, resulting in MAC database instability
Trang 7Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 7
Issues with Layer 1 Redundancy:
Broadcast Storms
frames caught in a Layer 2 loop that all available bandwidth is
consumed It is also known as denial of service
traffic is caught within the loop; thus consuming more resources
network to fail
Trang 8Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 8
Issues with Layer 1 Redundancy:
Broadcast Storms
Trang 9Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 9
Issues with Layer 1 Redundancy:
Duplicate Unicast Frames
frames arriving at the destination device
with, duplicate transmissions
recognize and eliminate endlessly looping frames
Trang 10Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 10
Issues with Layer 1 Redundancy:
Duplicate Unicast Frames
Trang 11Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 11
Spanning Tree Algorithm: Introduction
destinations on the network by intentionally blocking redundant
paths that could cause a loop
entering or leaving that port This does not include bridge protocol
data unit (BPDU) frames that are used by STP to prevent loops
The physical paths still exist to provide redundancy, but these
paths are disabled to prevent the loops from occurring
switch failure, STP recalculates the paths and unblocks the
necessary ports to allow the redundant path to become active
Trang 12Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 12
Spanning Tree Algorithm: Introduction
Trang 13Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 13
Spanning Tree Algorithm: Introduction
Trang 14Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 14
Spanning Tree Algorithm: Introduction
Trang 15Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 15
Spanning Tree Algorithm: Port Roles
Trang 16Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 16
Spanning Tree Algorithm: Root Bridge
Trang 17Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 17
Spanning Tree Algorithm: Path Cost
Trang 18Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 18
802.1D BPDU Frame Format
Trang 19Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 19
BPDU Propagation and Process
Trang 20Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 20
BPDU Propagation and Process
Trang 21Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 21
Extended System ID
STP was enhanced to include support for VLANs, requiring the
VLAN ID to be included in the BPDU frame through the use of the
extended system ID
Trang 22Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 22
Extended System ID
In the example, the priority of all the switches is 32769 The value is
based on the 32768 default priority and the VLAN 1 assignment
associated with each switch (32768+1)
Trang 23© 2008 Cisco Systems, Inc All rights reserved Cisco Confidential
Tree Protocols
Trang 24Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 24
List of Spanning Tree Protocols
Trang 25Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 25
Characteristics of the Spanning Tree
Protocols
Trang 26Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 26
Overview of PVST+
Networks running PVST+ have these characteristics:
each VLAN in the network
a considerable waste of CPU cycles for all the switches in the
network In addition to the bandwidth that is used for each instance
to send its own BPDU
Trang 27Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 27
Overview of PVST+
Trang 28Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 28
Port States and PVST+ Operation
STP introduces the five port states:
Trang 29Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 29
Extended System ID and PVST+
Operation
switch has a unique BID for each VLAN
32768, plus the extended system ID of 2
Trang 30Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 30
Overview of Rapid PVST+
RSTP is the preferred protocol for preventing Layer 2 loops in a
switched network environment
each VLAN
state
discarding, learning, or forwarding
backward compatibility
the version field is set to 2 to indicate RSTP, and the flags field
uses all 8 bits
Trang 31Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 31
Overview of Rapid PVST+
Trang 32Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 32
RSTP BPDU
Trang 33Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 33
Edge Ports
Trang 34Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 34
Link Types
The link type can determine whether the port can immediately
transition to forwarding state Edge port connections and
point-to-point connections are candidates for rapid transition to forwarding
state
Trang 35© 2008 Cisco Systems, Inc All rights reserved Cisco Confidential
Configuration
Trang 36Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 36
Catalyst 2960 Default Configuration
Trang 37Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 37
Configuring and Verifying the Bridge ID
Trang 38Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 38
Configuring and Verifying the Bridge ID
Trang 39Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 39
PortFast and BPDU Guard
configured with PortFast
that port transitions from
Trang 40Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 40
PVST+ Load Balancing
Trang 41Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 41
PVST+ Load Balancing
Another method to specify the root bridge is to set the spanning
tree priority on each switch to the lowest value so that the switch is
selected as the primary bridge for its associated VLAN
Trang 42Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 42
PVST+ Load Balancing
Display and verify spanning tree configuration details
Trang 43Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 43
PVST+ Load Balancing
Trang 44Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 44
Spanning Tree Mode
Rapid PVST+ is the Cisco
implementation of RSTP It
supports RSTP on a
per-VLAN basis
Trang 45Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 45
Analyzing the STP Topology
Trang 46Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 46
Expected Topology versus Actual Topology
Trang 47Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 47
Overview of Spanning Tree Status
Trang 48Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 48
Spanning-Tree Failure Consequences
one or more ports into the
forwarding state
by a switch enters the
loop
Trang 49Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 49
Repairing a Spanning Tree Problem
redundant links in the switched network, either physically or
through configuration, until all loops are eliminated from the
topology
cause of the spanning-tree failure
Carefully monitor the network to ensure that the problem is fixed
Trang 50© 2008 Cisco Systems, Inc All rights reserved Cisco Confidential
Protocols
Trang 51Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 51
Default Gateway Limitations
cannot be reached, the
local device is unable
to send packets off the
local network segment
which these devices
can determine the
address of a new
default gateway
Trang 52Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 52
single router to the
hosts on the LAN
Trang 53Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 53
Steps for Router Failover
Trang 54Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 54
First-Hop Redundancy Protocols
Trang 55Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 55
First-Hop Redundancy Protocols
Trang 56Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 56
HSRP Verification
Trang 57Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 57
GLBP Verification
solution to allow automatic selection and simultaneous use of
multiple available gateways in addition to automatic failover
between those gateways
Trang 58© 2008 Cisco Systems, Inc All rights reserved Cisco Confidential
Trang 59Presentation_ID © 2008 Cisco Systems, Inc All rights reserved Cisco Confidential 59
basis in the form of PVST+ This is the default configuration on
Cisco switches
in the form of Rapid PVST+
proactively to enable spanning tree load balancing
provide alternate default gateways for hosts in the switched
environment