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CIE Program Project 2 - A Campus Network Design

Technical Report · January 2021

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 ‫هندسة االتصاالت و الحاسبات‬
‫كليـــة الهندســـة‬
‫جامعـــة المنصـــورة‬

Design of Campus
Communication Network
BSc Comm. & Computers Eng.

Assist Prof. Mohammed M. Ashour

Eng. Haitham Mahmoud Abd-Elghany

Team
Omar Mokhtar Mohamed Ahmed Mahmoud
Mohamed Mahmoud Hussien
Mahmoud Ahmed Gaber Akram Mohamed Aly
Thabet Attiya
Ahmed Wed Abdul-Azim Gamal Hussien Ebrahiem
Attiya Mohamed
Ahmed Khaled Mohamed Mohamed Aly Al-saied Aly
Esmaiel

29 March 2021
 Design of Campus Communication Network

Abstract
In this project a computer network made up of an interconnection of
local area networks (LANs) within a limited geographical area.

Through a blend of theory and the VMware (TM) program, we

develop the backbone necessary for our project to work in high
demand areas of network support, user support, and security.

We use GNS3 to emulate, configure, test and troubleshoot our network.

A campus area network is larger than a local area network but

smaller than a metropolitan area network (MAN) or wide area
network (WAN).

First, we use packet tracer to simulate an imaginary network design.

Then, we design a real Campus network and make it Suitable for our
capabilities to move to GNS3 to emulate, configure, test and
troubleshoot the network.

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Table of Contents
Abstract..................................................................................................................1

Table of Contents....................................................................................................2

Chapter 1: Introduction...........................................................................................4
About Project's Tools.................................................................................................4
Packet Tracer.........................................................................................................5
VMware.................................................................................................................6
GNS3......................................................................................................................7
First Topology in GNS3 & VMware............................................................................8
The final topology..................................................................................................... 9

Chapter2: Multilayer Switching.............................................................................10

What Is a Multilayer Switch?.................................................................................. 10
Why Use a Multilayer Switch?.................................................................................13
How to Use a Multilayer Switch?............................................................................14
Multilayer Switch Port Types...................................................................................15
Conclusion............................................................................................................... 17

Chapter3: Redundancy and Load Balancing...........................................................18

What Is Redundancy in Networking?......................................................................18
Forms of Network Redundancy...............................................................................19
What Is Load balancing in Networking?..................................................................20
Benefits of Load Balancing...................................................................................21
Gateway Load Balancing Protocol (GLBP)...............................................................22
Facts about GLBP.................................................................................................23
Close view of the Topology......................................................................................24
Configuration.......................................................................................................... 25
Testing.....................................................................................................................29
Debugging...............................................................................................................36

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Chapter4: EtherChannel.........................................................................................42
What is the EtherChannel?......................................................................................42
Benefits of EtherChannel.........................................................................................43
EtherChannel Requirements....................................................................................45
EtherChannel Load-Balancing.................................................................................46
Configuration.......................................................................................................... 47
EtherChannel – Manual Configuration................................................................53
EtherChannel – Dynamic Configuration...............................................................54
EthernChannel - PAgP............................................................................................. 55
EtherChannel - LACP................................................................................................56
Troubleshooting EtherChannel................................................................................57

Chapter5: Spanning Tree protocol.........................................................................65

Basic STP Configuration...........................................................................................71
STP Port States........................................................................................................73
Improving STP Convergence....................................................................................77
Troubleshoot........................................................................................................... 82
Troubleshoot a Failure.........................................................................................82
Use the Diagram of the Network.........................................................................82
Identify a Bridging Loop.......................................................................................83
Log STP Events on Devices That Host Blocked Ports............................................83
Debug spanning-tree...........................................................................................84
show spanning-tree.............................................................................................85
show spanning-tree summary totals...................................................................86

Chapter6: Conclusion.............................................................................................87
This is the final network..........................................................................................88

Appendices............................................................................................................89

References............................................................................................................90

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Chapter 1:
Introduction
The increasing demand for high performance network has
challenged network researchers to design network architectures
capable of delivering a high quality of service to end users.

The network infrastructure design becomes critical part for universities.

An important network design consideration for today's networks is

creating the potential to support future expansions; reliable and
scalable networks. This requires to define the client's unique
situation, particularly the current technology, application, and data
architecture.

About Project's Tools

Many network design tools and methodologies in use today

resemble the connect-the-dots game that some of us played as
children.

These tools let you place internetworking devices on a palette and

connect them with local-area network (LAN) or wide-area network
(WAN) media.

The problem with this methodology is that it skips the steps of

analyzing a customer's requirements and selecting devices and
media based on those requirements.

Good network design must recognize that a customer's

requirements embody many business and technical goals including
requirements for availability, scalability, affordability, security, and

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manageability.

High-availability of the network has always been important in the

internetworking world.

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Packet Tracer

What is Packet Tracer? Packet Tracer is a cross-platform visual

simulation tool designed by Cisco Systems that allows users to
create network topologies and imitate modern computer networks.
Packet Tracer (PT) is a powerful and dynamic tool that displays the
various protocols used in networking, in either Real Time or
Simulation mode. This includes layer 2 protocols such as Ethernet
and PPP, layer 3 protocols such as IP, ICMP, and ARP, and layer 4
protocols such as TCP and UDP. Routing protocols can also be
traced.

We use it to make a first design and configuration to our network

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VMware

VMware Workstation 9 continues VMware’s tradition of delivering

the virtual hardware that technical professionals deserve and rely
on every day. With support for Windows 8, restricted VMs, Open GL
support for Linux and a new web interface to access virtual
machines, it’s the perfect tool for getting work done.

To help you and your organization evaluate Windows 8, master the

Metro UI and test your applications, VMware Workstation 9 is
optimized for running Windows 8 virtual machines and running on
Windows 8 PCs. Easy Install simplifies the task of creating
Windows 8 virtual machines, Unity mode will intelligently scale
windows with Metro applications and multi-touch support will
ensure you get the true Windows 8 experience in a virtual
machine.

Workstation’s new web interface allows you to access your virtual

machines running in Workstation or vSphere on a tablet, smart
phone, PC or any device with a modern browser. No plugins
necessary. Now you can power on, off, or suspend your virtual
machines and interact with them from almost anywhere.

Create virtual machines that are encrypted, block USB devices,

require a runtime password, and another password to change
virtual machine settings. Once set, send the virtual machine

To anyone to run on their Mac, Windows, or Linux machines by

using VMware Fusion Professional. From PC to Datacenter and Back
Again in Workstation 8 we introduced the ability to upload a virtual
machine from your PC to vSphere. Workstation 9 takes the next
step and allows you to drag and drop a virtual machines form
vSphere to your PC. It’s the easiest way to move virtual machines
between your PC and your internal cloud.

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GNS3

GNS3 is used by hundreds of thousands of network engineers

worldwide to emulate, configure, test and troubleshoot virtual and
real networks. GNS3 allows you to run a small topology consisting of
only a few devices on your laptop, to those that have many devices
hosted on multiple servers or even hosted in the cloud.

GNS3 consists of two software components:

 The GNS3-all-in-one software (GUI)

 The GNS3 virtual machine (VM)

When you create topologies in GNS3 using the all-in-one software

GUI client, the devices created need to be hosted and run by a
server process. You have a few options for the server part of the
software:

1. Local GNS3 server

2. Local GNS3 VM
3. Remote GNS3 VM

The local GNS3 server runs locally on the same PC where you
installed the GNS3 all-in-one software. If for example you are using
a Windows PC, both the GNS3 GUI and the local GNS3 server are
running as processes in Windows.

GNS3 supports both emulated and simulated devices.

Emulation: GNS3 mimics or emulates the hardware of a device and

you run actual images on the virtual device. For example, you
could copy the Cisco IOS from a real, physical Cisco router and run
that on a virtual, emulated Cisco router in GNS3.

Simulation: GNS3 simulates the features and functionality of a

device such as a switch. You are not running actual operating
systems (such as Cisco IOS), but rather, a simulated device
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developed by GNS3, like the built-in layer 2 switch.

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First Topology in GNS3 & VMware

We move to GNS3 & VMware to move to GNS3 to emulate,

configure, test and troubleshoot the network.

This is the First Topology in GNS3

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The final topology

Then, we decrease the number of PCs and remove the Clouds

because of appropriate capabilities. And this is the final topology
which is Configured and tested.

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Chapter2:
Multilayer Switching
With the increasing diversity of network applications and the
implementation of some converted networks, the multilayer
switch is thriving in data centers and networks. It is regarded as a
technology to enhance the network routing performance on LANs.

What Is a Multilayer Switch?

The multilayer switch (MLS) has 10gbe switch and Gigabit Ethernet
switch. It is a network device which enables operation at multiple
layers of the OSI model. By the way, the OSI model is a reference
model for describing network communications. It has seven layers,
including the physical layer (layer 1), data link layer (layer 2),
network layer (layer 3) and so on. The multilayer switch performs
functions up to almost application Layer (layer 7). For instance, it
can do the context based access control, which is a feature of layer
7. Unlike the traditional switches, multilayer switches also can bear
the functions of routers at incredibly fast speeds. In addition, the
Layer 3 switch is one type of multilayer switches and is very
commonly used.

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Figure 1: Seven layers in OSI model

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Multilayer Switch vs. Layer 2 Switch

The Layer 2 switch forwards data packets based on the Layer 2

information like MAC addresses. As a traditional switch, it can
inspect frames. While multilayer switches not only can do all the job
that Layer 2 switches do, it has routing function as well, including
static routing and dynamic routing. So multilayer switches can
inspect deeper into the protocol description unit.

Multilayer Switch vs. Router

Generally, multilayer switches and routers have three key

differences. Firstly, routers typically use software to route. While
multilayer switches route packets on ASCI (Application Specific
Integrated Circuit) hardware. Another difference is that multilayer
switches route packets faster than routers. In addition, based on IP
addresses, routers can support numerous different WAN
technologies. However, multilayer switches lack some QoS (Quality
of Service) features. It is commonly used in LAN environment.

Routing Between VLANs

By default, a switch will forward both broadcasts and multicasts out

every port but the originating port. However, a switch can be logically
segmented into separate broadcast domains, using Virtual LANs (or
VLANs).

Each VLAN represents a unique broadcast domain:

 Traffic between devices within the same VLAN is switched.

 Traffic between devices in different VLANs requires a Layer-3
device to communicate.

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There are three methods of routing between VLANs. The first method
involves using an external router with a separate physical interface in
each VLAN. This is the least scalable solution, and impractical for
environments with a large number of VLANs:

The second method involves using an external router with a single

trunk link to the switch, over which all VLANs can be routed. The
router must support either 802.1Q or ISL encapsulation. This method
is known as router-on-a- stick:

The final method involves using a multilayer switch, which supports

both Layer-2 and Layer-3 forwarding:

Multilayer switching is a generic term, encompassing any switch that

can forward traffic at layers higher than Layer-2.

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Why Use a Multilayer Switch?

As mentioned above, the multilayer switch plays an important role

in network setups. The following highlights some of the advantages.

 Easy for use – Multilayer switches are configured automatically

and its Layer 3 flow cache is set up autonomously. And there is
no need for you to learn new IP switching technologies for its
“plug-and-play” design.

 Faster connectivity – With multilayer switches, you gain the

benefits of both switching and routing on the same platform.
Therefore, it can meet the higher-performance need for the
connectivity of intranets and multimedia applications.

Figure 2: Multilayer switches

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How to Use a Multilayer Switch?

Generally, there are three main steps for you to configure a multilayer switch.

Preparation

 Determine the number of VLANs that will be used, and the IP

address range (subnet) you’re going to use for each VLAN.
 Within each subnet, identify the addresses that will be used for
the default gateway and DNS server.
 Decide if you’re going to use DHCP or static addressing in each VLAN.

Configuration

You can start configuring the multilayer switch after making preparations.

 Enable routing on the switch with the IP routing command.

(Note: some multilayer switches may support the protocols like
RIP and OSPF.)
 Log into multilayer switch management interface.
 Create the VLANs on the multilayer switch and assign ports to each VLAN.

Verification

After completing the second step, you still need to offer a snapshot
of the routing table entries and list a summary of an interface’s IP
information and status. Then, the multilayer switch configuration is
finished.

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Multilayer Switch Port Types

Multilayer switches support both Layer-2 and Layer-3 forwarding.

Layer-2 forwarding, usually referred to as switching, involves

decisions based on frame or data-link headers. Switches will build
hardware address tables to intelligently forward frames.

Layer-3 forwarding, usually referred to as routing, involves decisions

based on packet or network headers. Routers build routing tables to
forward packets from one network to another.

A multilayer switch supports three port types:

 Layer-2 or switchports
 Layer-3 or routed ports
 Switched Virtual Interfaces (SVIs)

A switchport can either be an access or trunk port. By default on Cisco

switches, all interfaces are switchports. To manually configure an
interface as a switchport:

Switch(config)# interface gi1/10

Switch(config-if)# switchport

A routed port behaves exactly like a physical router interface, and is

not associated with a VLAN. The no switchport command configures
an interface as a routed port, allowing an IP address to be assigned:

Switch(config)# interface gi1/20

Switch(config-if)# no switchport

Switch(config-if)# ip address 10.101.101.1 255.255.255.0

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Multilayer switches support configuring a VLAN as a logical routed

interface, known as a Switched Virtual Interface (SVI). The SVI is
referenced by the VLAN number:

Switch(config)# interface vlan 101

Switch(config-if)# ip address 10.101.101.1 255.255.255.0

Switch(config-if)# no shut

SVIs are the most common method of configuring inter-VLAN

routing. The logical VLAN interface will not become online unless:

 The VLAN is created.

 At least one port is active in the VLAN.

Multilayer Switching – Route Once, Switch Many

Originally, multilayer switches consisted of two independent components:

 Routing engine
 Switching engine

The first packet in an IP traffic flow must be sent to the routing

engine to be routed. The switching engine could then cache
this traffic flow.
Subsequent packets destined for that flow could then be
switched instead of routed. Thisgreatly reduced forwarding
latency.

This concept is often referred to as route once, switch many.

Just like a router, a multilayer switch must update the

following header information

 Layer 2 destination address

 Layer 2 source address

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 Layer 3 IP Time-to-Live (TTL)

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Additionally, the Layer-2 and Layer-3 check sums must be

updated to reflectthe changes in header information.

Cisco’s original implementation of multilayer switching was

known as NetFlow or route-cache switching. NetFlow
incorporated separate routingand switching engines.

NetFlow was eventually replaced with Cisco Express Forwarding (CEF),

Which addressed some of the disadvantages of NetFlow:

 CEF is less CPU intensive.
 CEF does not dynamically cache routes, eliminating
the risk ofstale routes in the cache if the routing
topology changes.

Conclusion

The multilayer switch provides high functions in the networking. It is

suitable for VLAN segmentation and better network performance.
When buying multilayer switches, you’d better take multilayer
switch price and using environment into consideration.

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Chapter3:
Redundancy and Load
Balancing
- What Is Redundancy in Networking?

Network redundancy is the process of adding additional

instances of network devices and lines of communication to
help ensure network availability and decrease the risk of failure
along the critical data path.

The underlying premise that explains the importance of network

redundancy is simple. Without any backup systems in place, all it
takes is one point of failure in a network to disrupt or bring down an
entire system. Redundancy in networks helps to eliminate single
points of failure to ensure better network stability and uptime in
the face of events that would otherwise take the network offline.
Consider the following example:

To reach other networks, HostA must utilize a single gateway – SwitchA.

The gateway represents a single point of failure on this network. If the

gateway fails, hosts will lose access to all resources beyond the
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gateway.

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- Forms of Network Redundancy:

Generally speaking, there are two forms of redundancy that data

centers use to ensure systems will stay up and running:

 Fault Tolerance: A fault-tolerant redundant system provides full

hardware redundancy, mirroring applications across two or
more identical systems that run in tandem. Should anything
go wrong with the primary system, the mirrored backup
system will take over with no loss of service. Ideal for any
operations in which any amount of downtime is unacceptable
(such as industrial or healthcare applications), fault-
tolerance redundant systems are complex and often
expensive to implement.

 High Availability: A software-based redundant system, high

availability uses clusters of servers that monitor one another
and have failover protocols in place. If something goes wrong
with one server, the backup servers take over and restart
applications that were running on the failed server. This
approach to network redundancy is less infrastructure
intensive, but it does tolerate a certain amount of downtime in
that there is a brief loss of service while the backup servers
boot up applications.

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Using multiple routers or multilayer switches can provide Layer-

3 redundancy for hosts:

However, the Layer-3 redundancy must be transparent to each host.

Hosts should not be configured with multiple default gateways.

- What Is Load balancing in Networking?

Load balancing is a standard functionality of the Cisco IOS® router

software, and is available across all router platforms. It is inherent
to the forwarding process in the router and is automatically
activated if the routing table has multiple paths to a destination. It
is based on standard routing protocols, such as Routing Information
Protocol (RIP), RIPv2, Enhanced Interior Gateway Routing Protocol
(EIGRP), Open Shortest Path First (OSPF), and Interior Gateway
Routing Protocol (IGRP), or derived from statically configured routes
and packet forwarding mechanisms. It allows a router to use
multiple paths to a destination when forwarding packets.

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Benefits of Load Balancing

 Reduced Downtime
 Scalable
 Redundancy
 Flexibility
 Efficiency
 Global Server Load Balancing

Cisco supports three protocols to provide transparent Layer-3 redundancy:

 Hot Standby Router Protocol (HSRP)

 Virtual Router Redundancy Protocol (VRRP)
 Gateway Load Balancing Protocol (GLBP)

Why we will Use Gateway Load Balancing Protocol

(GLBP)?

- Because GLBP allows the load balancing of traffic among the

master and standby routers while in HSRP (and VRRP) the standby
routers do not help handle traffic. With GLBP, the single virtual IP
address is associated with one virtual MAC address per GLBP
member. The master receives ARP requests and sends replies that
specify different virtual MAC addresses, taking turns among the
different virtual MAC addresses in order to distribute traffic among
them.

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Gateway Load Balancing Protocol (GLBP)

- To overcome the shortcomings in HSRP and VRRP, Cisco

developed the proprietary Gateway Load Balancing Protocol
(GLBP).

- Routers are added to a GLBP group, numbered 0 to 1023. Unlike

HSRP and VRRP, multiple GLBP routers can be active, achieving both
redundancy and load balancing.

- A priority is assigned to each GLBP interface - 100 by default. The

interface with the highest priority becomes the Active Virtual
Gateway (AVG). If priorities are equal, the interface with the highest
IP will become the AVG.

- Routers in the GLBP group are assigned a single virtual IP

address. Hosts will use this virtual address as their default
gateway. The AVG will respond to ARP requests for the virtual IP
with the virtual MAC address of an Active Virtual Forwarder (AVF).

- Up to three routers can be elected as AVFs. The AVG assigns a

virtual MAC address to each AVF, and to itself, for a maximum total
of 4 virtual MAC addresses. Only the AVG and AVFs can forward
traffic for hosts.
Any router not elected as an AVF or AVG will become a Secondary
Virtual Forwarder (SVF), and will wait in standby until an AVF fails.

- GLBP supports three load balancing methods:

- Round Robin
- Weighted
- Host-dependent

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- The default load balancing method is per-host round robin. Traffic

from hosts is distributed equally across all routers in the GLBP
group. The AVG will respond to the first host ARP request with the
first virtual MAC address. The second ARP request will receive the
second virtual MAC address, etc.

- The weighted load balancing method will distribute traffic

proportionally, based on a router’s weight. Routers with a higher
weight will receive a proportionally higher percentage of traffic.

- Host-dependent load balancing will provide a host device with the same
Virtual MAC address every time it performs an ARP request.

- Hello packets are used to elect GLBP roles and to ensure all
routers are functional. If the current active router fails, the standby
router will immediately take over as active, and a new standby is
elected. By default, hello packets are sent every 3 seconds

- Facts about GLBP:

 Hello packets are sent every 3 seconds.

 Hello packets are sent to multicast address 224.0.0.102.
 The default hold down time is 10 seconds.
 The virtual MAC address is the reserved 0007.b4xx.xxyy, with xxxx

Representing the GLBP group number, and yy representing the

AVF Number.

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Close view of the Topology

 We used 4 multilayer switches and many access

switches and a lot of number of hosts.

 Assigned a single virtual IP address (10.16.8.1). Hosts

will use this virtual address as their default gateway.

 The AVG will respond to ARP requests for the virtual

IP with the virtual MAC address of an Active Virtual
Forwarder (AVF).

 Assigned a priority to the multilayer switches to elect

the AVG and the AVF.

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Configuration

For Switch 1

- This Switch will be AVF.

- Using Load-Balancing method: Round-Robin.
- With Virtual GLBP Ip = 10.16.8.1
- Priority = 50

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For Switch 2

- This Switch will be AVF.

- Using Load-Balancing method: Round-Robin.
- With Virtual GLBP Ip = 10.16.8.1
- Preempt: Enable
- Priority = 100 (default)

About Preempt: The preempt parameter will allow a router to

forcibly assume the role of AVG if it fails and return when its
priority allow to give it a role of AVG.

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For Switch 3

- This Switch will be AVF.

- Using Load-Balancing method: Round-Robin.
- With Virtual GLBP Ip = 10.16.8.1
- Preempt: Enable
- Priority = 150

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For Switch 4

- This Switch will be AVG.

- Using Load-Balancing method: Round-Robin.
- With Virtual GLBP Ip = 10.16.8.1
- Preempt: Enable
- Priority = 200

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Testing

Show Glbp

Let’s dissect this output piece by piece and talk about what it means.

The top portion of the output talks about who the AVG is, as
well as the general state of the group.

Vlan8 – Group 1
State is Active

The first line tells about the group we are looking at as well as the
interface that GLBP is running on. The second line tells us that this
router in the Active AVG.

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The next chunk of output gives us some general information about

the local GLBP host as well as the group in general. We can see the
virtual IP that the group is responsible for which was configured on
all of the hosts to star the GLBP process. We can also see the local
priority of this GLBP host. As the output, states this is the default
value. The priority is used to determine who the active AVG is. The
router with the highest AVG will always be the AVG, and the second
highest will always be the SVG.

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Glbp brief

- Switch 1

-Switch 2

- Switch 3

- Switch 4

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So all the other switches know who the AVG is as well as who
the SVG is. Switch3 is the SVG so he marks himself as ‘local’
under the Standby router field…

Now let’s take a look at the output of the ‘show glbp brief’
command on Swittch4…

As you can see, Switch4 is now the active AVG with Switch3 (with
the second highest priority) being the SVG.

- Let’s take a second to talk about the output from this command.

- Show glbp brief…

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- The First line in the output talks about the group in general. It tells
you the priority of the AVG, the GLBP group IP, the AVG and the
SVG. In this case, the priority of the AVG is 200, the group IP is
10.16.8.1, the AVG is local, and the SVG is switch3.

- The Second line talks about the first virtual forwarder. The state
is shown as active here since the third AVF is the local router itself.
This shows that a switch can own both the AVG as well as the AVF
roles. We see the virtual MAC as well as ‘local’ to indicate that this
router has this role

- The Third line talks about the second AVF in the group. The
meaning of the ‘state’ column changes here slightly. As far as
switch4 is concerned, it is listening to this AVF to make sure that it
is still online. This does NOT imply that this AVF is not active. This
is just the view point from switch4. The rest of the line shows the
virtual MAC that this AVF is responsible for as well as the router’s
IP address.

- The Fourth line talks about the third virtual forwarder. Again, from
switch4’s perspective it is listening to this AVF. We see the virtual
MAC that this AVF is using and responsible for as well as its IP
address.

- The Fifth line shows the fourth AVF, its virtual MAC and IP address.

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- In Command ( Show Glbp )..

GLBP supports three load balancing methods:

•Round Robin

•Weighted

•Host-dependent

The default load balancing method is per-host round robin. Traffic

from hosts is distributed equally across all routers in the GLBP
group. The AVG will respond to the first host ARP request with the
first virtual MAC address. The second ARP request will receive the
second virtual MAC address, etc.

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The default weight is 100.

 If the weight falls below the lower threshold, the router must
stop functioning as an AVF. The router will become an AVF
again once its weight reaches the upper threshold, as long
as preempt is configured.

 Hello packets are sent every 3 seconds.

 Hello packets are sent to multicast address 224.0.0.102.

 The default hold down time is 10 seconds.

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Debugging

Debug Glbp

-Debug Glbp Errors

To display debugging messages about Gateway Load Balancing

Protocol (GLBP) error conditions, use the debug glbp errors
command in privileged EXEC mode. To disable debugging output,
use the no form of this command.

- Debug glbp errors

- No debug glbp errors

Examples

The following is sample output from the debug glbp errors

command: Router# debug glbp errors

GLBP Errors debugging is on

1d19h: GLBP: Fa0/0 API active virtual address 10.21.8.32
not found 1d19h: GLBP: Fa0/0 API active virtual address
10.21.8.32 not found 1d19h: GLBP: Fa0/0 API active virtual
address 10.21.8.32 not found

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Debug glbp Events

To display debugging messages about Gateway Load Balancing

Protocol (GLBP) events that are occurring, use the debug glbp events
command in privileged EXEC mode. To disable debugging output,
use the no form of this command.

- debug glbp events [all | detail | terse]

- no debug glbp events [all | detail | terse]

Examples

The following is sample output from the debug glbp

events command when the terse keyword is
specified:

Router# debug glbp events terse

GLBP Events debugging is

on (Protocol, redundancy,
track)

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Debug glbp Packets

To display summary information about Gateway Load Balancing

Protocol (GLBP) packets being sent or received, use the debug glbp
packets command in privileged EXEC mode. To disable debugging
output, use the no form of this command.

- debug glbp packets [all | detail | hello | reply | request | terse]

- no debug glbp packets [all | detail | hello | reply | request | terse]

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Examples

The following is sample output from the debug glbp packets

command: Router# debug glbp packets hello

GLBP Packets debugging is on

(Hello)
1d19h: GLBP: Fa0/0 Grp 10 Hello out 10.21.8.32 VG Active pri 254 vIP
10.21.8.10 1

1d19h: GLBP: Fa0/0 Grp 10 Hello out 10.21.8.32 VG Active pri 254 vIP
10.21.8.10 1

1d19h: GLBP: Fa0/0 Grp 10 Hello out 10.21.8.32 VG Active pri 254 vIP
10.21.8.10 1

1d19h: GLBP: Fa0/0 Grp 10 Hello out 10.21.8.32 VG Active pri 254 vIP
10.21.8.10 1

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Debug glbp Terse

To display a limited range of debug messages about Gateway Load

Balancing Protocol (GLBP) errors, events, and packets, use the
debug glbp
terse command in privileged EXEC mode. To disable debugging
output, use the no form of this command.

- debug glbp terse

- no debug glbp terse

Examples

The following is sample output from the debug glbp terse

command: Router# debug glbp terse

GLBP:
GLBP Errors debugging is on

GLBP Events debugging is on

(protocol, redundancy, track)

GLBP Packets debugging is on

(Request, Reply)

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Chapter4:
EtherChannel

-What is the EtherChannel?

EtherChannel is a port link aggregation technology or port-channel

architecture used primarily on Cisco switches.

It allows grouping of several physical Ethernet links to create one

logical Ethernet link for the purpose of providing fault-tolerance and
high-speed links between switches, routers and servers.

An EtherChannel can be created from between two and eight active

Fast, Gigabit or 10-Gigabit Ethernet ports, with an additional one to
eight inactive (failover) ports which become active as the other
active ports fail.

EtherChannel is primarily used in the backbone network, but can

also be used to connect end user machines.

EtherChannel technology was invented by Kalpana and

conceptualized by Kalpana employee Scott Childs in the early
1990s. It was later acquired by Cisco Systems in 1994. In 2000
the IEEE passed 802.3ad which is
an open standard version of EtherChannel.

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-Benefits of EtherChannel:

Using an EtherChannel has numerous advantages, and probably the

most desirable aspect is the bandwidth.

Using the maximum of 8 active ports a total bandwidth of

800 Mbit/s, 8 Gbit/s or 80 Gbit/s is possible depending on
port speed.

This assumes there is a traffic mixture, as those speeds do not

apply to a single application only. It can be used with Ethernet
running on twisted pair wiring, single-mode and multimode fiber.

Because EtherChannel takes advantage of existing wiring it makes

it very scalable. It can be used at all levels of the network to create
higher bandwidth links as the traffic needs of the network increase.
All Cisco switches have the ability to support EtherChannel.

-What is the port aggregation?

A network will often span across multiple switches. Trunk ports are
usually Used to connect switches together.
There are two issues with using only a single physical port for
the trunk Connection:-

•The port represents a single point of failure. If the port

goes down, the trunk connection is lost.
•The port represents a traffic bottleneck.
All other ports on the switch will use that one port to communicate
across the trunk connection.

Thus, the obvious benefits of adding redundancy to the trunk

connection are fault tolerance and increased bandwidth, via load
balancing.

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However, simply trunking two or more ports between the switches

will not Work, as this creates a switching loop.

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One of two things will occur:-

•Spanning Tree Protocol (STP) will disable one or more ports to

eliminate the loop.
•If STP is disabled, the switching loop will result in an almost.

Port aggregation allows multiple physical ports to be bundled

together to Form a single logical port.
The switch and STP will treat the bundled ports as a single interface,
eliminating the possibility of a switching loop.

Cisco’s implementation of port aggregation is called

EtherChannel. EtherChannel supports Fast, Gigabit, and 10
Gigabit Ethernet ports. A maximum of 8 active ports are
supported in a single EtherChannel.

If the ports are operating in full duplex, the maximum theoretical

bandwidth Supported is as follows:-

Fast Ethernet / Gigabit Ethernet / 10 Gigabit Ethernet

The maximum number of supported EtherChannel on a single
switch is Platform-dependent, though most support up to 64 or
128 EtherChannel.

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EtherChannel Requirements:

The previous section described the benefits of port aggregation for

a trunk Connection. However, EtherChannel can be formed with
either access or trunk ports.

EtherChannel are also supported on Layer-3 interfaces.

Implementing an EtherChannel for access ports provides
increased bandwidth and redundancy to a host device, such
as a server.
However, the host device must support a port aggregation protocol,
such as LACP.
Port aggregation protocols are covered in great detail later in this
guide. Similarly, implementing EtherChannel for trunk connections
provides increased bandwidth and redundancy to other switches.

If a port in an EtherChannel bundle fails, traffic will be redistributed

across the remaining ports in the bundle. This happens nearly
instantaneously.

For an EtherChannel to become active, all ports in the bundle

must be configured identically, regardless if the EtherChannel
is being used with access or trunk ports. Port settings that
must be identical include the Following:-
•Speed settings.
•Duplex settings.
•STP settings.
•VLAN membership (for access ports).

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•Native VLAN (for trunk ports).
•Allowed VLANs (for trunk ports).
•Trucking encapsulation protocol (for trunk ports).

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EtherChannel Load-Balancing:

Traffic sent across an EtherChannel is not evenly distributed across

all ports in the bundle.
Instead, EtherChannel utilizes a load-balancing algorithm to
determine the port to send the traffic out, based on one of several
criteria:-

•Source IP address - src-ip.

•Destination IP address - dst-ip.
•Source and destination IP address - src-dst-ip.
•Source MAC address - src-mac.
•Destination MAC address - dst-mac.
•Source and Destination MAC address - src-dst-mac.
•Source TCP/UDP port number - src-port.
•Destination TCP/UDP port number - dst-port.
•Source and destination port number - src-dst-port.

Using a deterministic algorithm prevents perfect load-balancing.

However, a particular traffic flow is forced to always use the same
port in the bundle, preventing out-of-order delivery.

The default load-balancing method for a Layer-2 EtherChannel is

either srcmac or src-dst-mac, depending on the platform.
The default method for a Layer-3 EtherChannel is src-dst-ip.

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Configuration

Switch 1 with switch 2

Switch1(config-if)#int range GigaEthernet

1/1-2 Switch1(config-if)#channel-group 5

mode desirable Switch1(config-if)#interface

port-channel 5 Switch1(config-if)#switchport

mode access Switch1(config-if)#switchport

access VLAN 8

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Switch 2 with Switch 1

Switch2(config-if)#int range GigaEthernet

0/2-3 Switch2(config-if)#channel-group 5

mode desirable Switch2(config-if)#interface

port-channel 5 Switch2(config-if)#switchport

mode access Switch2(config-if)#switchport

access VLAN 8

Switch 2 with switch 3

Switch2(config-if)#int range GigaEthernet

1/0-1 Switch2(config-if)#channel-group 6

mode desirable Switch2(config-if)#interface

port-channel 6 Switch2(config-if)#switchport

mode access Switch2(config-if)#switchport

access VLAN 8

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For Switch 3 with switch 2

Switch3(config-if)#int range GigaEthernet

0/2-3 Switch3(config-if)#channel-group 6

mode desirable Switch3(config-if)#interface

port-channel 6 Switch3(config-if)#switchport

mode access Switch3(config-if)#switchport

access VLAN 8

For Switch 3 with switch 4

Switch3(config-if)#int range GigaEthernet

1/0-1 Switch3(config-if)#channel-group 5

mode desirable

Switch3(config-if)#interface port-

channel 5 Switch3(config-

if)#switchport mode access

Switch3(config-if)#switchport access

VLAN 8

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For Switch 4 with switch 3

Switch4(config-if)#int range GigaEthernet

1/1-2 Switch4(config-if)#channel-group 5

mode desirable Switch4(config-if)#interface

port-channel 5 Switch4(config-if)#switchport

mode access Switch4(config-if)#switchport

access VLAN 8

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EtherChannel – Manual Configuration

There are two methods of configuring an EtherChannel:

• Manually
• Dynamically, using an aggregation protocol

To manually configure two ports to join an EtherChannel:

` Switch(config)# interface range gi2/23
- 24 Switch(config-if)# channel-group
1 mode on

The remote switch must also have the EtherChannel manually

configured as on. Remember that speed, duplex, VLAN, and STP
configuration must be configured identically across all participating
ports on both switches.

The channel-group number identifies the EtherChannel on the local

switch. This number does not need to match on both switches,
though for documentation purposes it should.

Adding switch ports to a channel-group creates a logical port-

channel interface. This interface can be configured by referencing
the channelgroup number:
Switch(config)# interface port-channel 1

Changes made to the logical port-channel interface are applied to

all physical switch ports in the channel-group:
Switch(config)# interface port-
channel 1 Switch(config-if)#
switchport mode trunk
Switch(config-if)# switchport trunk allowed vlan 50-100

To configure a port-channel as a Layer-3

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interface: Switch(config)# interface port-
channel 1 Switch(config-if)# no switchport
Switch(config-if)# ip address 192.168.10.1 255.255.255.0

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By default, a port-channel interface is administratively shutdown.

To bring the port-channel online:
Switch(config)# interface port-
channel 1 Switch(config-if)# no
shut

Physical port properties, such as speed and duplex, must be

configured on the physical interface, and not on the port-channel
interface.

EtherChannel – Dynamic Configuration

Cisco switches support two dynamic aggregation protocols:

• PAgP (Port Aggregation Protocol) – Cisco proprietary
aggregating protocol.
• LACP (Link Aggregation Control Protocol) – IEEE
standardized aggregation protocol, originally defined in
802.3ad.

Both PAgP and LACP exchange negotiation packets to form the

EtherChannel. When an EtherChannel is configured manually, no
negotiation packets are exchanged.

Thus, an EtherChannel will never form if one switch manually

configured the EtherChannel, and the other switch is using a
dynamic aggregation protocol.

PAgP and LACP are not compatible – both sides of an EtherChannel

must use the same aggregation protocol.

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EthernChannel - PAgP

PAgP is a Cisco-proprietary aggregation protocol, and supports two modes:

•Desirable – actively attempts to form a channel
•Auto – waits for the remote switch to initiate the channel

A PAgP channel will form in the following configurations:

• desirable ‫ـــــــــــ‬desirable
• desirable ‫ـــــــــــ‬auto

A channel will not form if both sides are set to auto. Also, PAgP will
not form a channel if the remote side is running LACP, or manually
configured.

To create an EtherChannel using PAgP

negotiation: Switch(config)# interface
range gi2/23 – 24 Switch(config-if)#
channel-protocol pagp Switch(config-if)#
channel-group 1 mode desirable
Switch(config-if)# channel-group 1 mode
auto

PAgP requires that speed, duplex, VLAN, and STP configuration be

configured identically across all participating ports.

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EtherChannel - LACP

LACP is an IEEE standard aggregation protocol, and supports two

modes: • Active – actively attempts to form a channel
•Passive – waits for the remote switch to initiate the channel

An LACP channel will form in the following configurations:

• active‫ ـــــــــــــ‬active
• active‫ ــــــــــــ‬passive

A channel will not form if both sides are set to passive. Also, LACP
will not form a channel if the remote side is running PAgP, or
manually configured.

To create an EtherChannel using LACP

negotiation: Switch(config)# interface
range gi2/23 – 24 Switch(config-if)#
channel-protocol lacp Switch(config-if)#
channel-group 1 mode active
Switch(config-if)# channel-group 1 mode
passive

LACP requires that speed, duplex, VLAN, and STP configuration be

configured identically across all participating ports.

Recall that a maximum of 8 active ports are supported in a single

EtherChannel. LACP supports adding an additional 8 ports into the
bundle in a standby state, to replace an active port if it goes down.

LACP assigns a numerical port-priority to each port, to determine

which ports become active in the EtherChannel. By default, the
priority is set to 32768, and a lower priority is preferred. If there is a

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tie in port-priority, the lowest port number is preferred.

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To change the LACP port-priority to something other than default:

Switch(config)# interface range gi2/23 – 24
Switch(config-if)# lacp port-priority 100

LACP also assigns a system-priority to each switch, dictated which

switch becomes the decision-maker if there is a conflict about active
ports. The default system-priority is 32768, and a lower priority is
again preferred. If there is a tie in system-priority, the lowest switch
MAC address is preferred.

To globally change the system-priority on a switch:

Switch(config)# lacp system-priority 500

Troubleshooting EtherChannel

To view status information on all configured

EtherChannels: Switch# show etherchannel summary

Flags:
D - Down
P - in port-
channel I -
stand-alone
s - Suspended
R - Layer3
S - Layer2
U - port-channel in use

Group Port-channel Ports

1 Po1(SU) Gi2/23(P) Gi2/24(P)

Note that both ports have a status of P, which indicates that they
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are up and active in the EtherChannel.

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On Cisco Nexus switches, the syntax for this command is slightly

different: NexusSwitch# show port-channel summary

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Chapter5:
Spanning Tree protocol
Switching loops:
When a switching loop is introduced into the network, a destructive
broadcast storm will develop within seconds. A storm occurs when
broadcasts are endlessly forwarded through the loop.
Consider the following example:

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If HostA sends out a broadcast, SwitchD will forward the broadcast

out all ports in the same VLAN. The broadcast will loop around the
switches infinitely and there will be a broadcast storm.

Spanning Tree Protocol (STP) was developed to prevent the

broadcast storms caused by switching loops. STP was originally
defined in IEEE 802.1D.
Switches running STP will build a map or topology of the entire
switching network. STP will identify if there are any loops, and then
disable or block as many ports as necessary to eliminate all loops in
the topology.
STP switches exchange Bridge Protocol Data Units (BPDU’s) to build
the topology database. BPDU’s are forwarded out all ports every
two seconds, to a dedicated MAC multicast address of
0180.c200.0000.

Building the STP topology is a multistep convergence process:

•A Root Bridge is elected
•Root ports are identified
•Designated ports are identified
•Ports are placed in a blocking state as required, to eliminate loops.

Root Bridge:
which is the central reference point for the STP topology is elected
based on its Bridge ID, comprised of two components in the original
802.1D standard:
•16-bit Bridge priority
•48-bit MAC address

the lowest priority wins. If there is a tie in priority, the lowest MAC
address is used as the tie-breaker.

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Consider the following example:

 SwitchB, SwitchC, and SwitchE have the default priority of 32,768.

 SwitchA and SwitchD are tied with a lower priority of 100.

 SwitchA has the lowest MAC address, and will be elected

the Root Bridge.

By default, a switch will always believe it is the Root Bridge,

until it receives a BPDU from a switch with a lower Bridge ID.
This is referred to as a superior BPDU.

The second step in the STP convergence process is to identify

root ports. The root port of each switch has the lowest root
path cost to get to the Root Bridge.

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Consider the following example:

 SwitchA has a cumulative path cost of 0, because it is the Root Bridge.

 SwitchB has two paths to the Root Bridge:

- A direct connection to SwitchA, with a path cost of 4.
- Another path through SwitchD, with a path cost of 16.

 SwitchD also has two paths to the Root Bridge:

- A path through SwitchB, with a path cost of 8.
- A path through SwitchE, with a path cost of 12

the port to switch is preferred and will become the root port.

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The third step in the STP convergence process is to identify

designated ports. A single designated port is identified for
each network segment. Similar to a root port, the designated
port is determined by the lowest cumulative path cost leading
the Root Bridge.

If two ports are eligible to become the designated port, then

there is a loop. One of the ports will be placed in a blocking
state to eliminate the loop.
Note: A port can never be both a designated port and a root
port. Consider the following example:

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Port ID:

When electing root and designated ports, it is possible to have a tie

in both path cost and Bridge ID. Consider the following example:
The bandwidth of both links is equal, thus both ports on SwitchB
have an equal path cost to the Root Bridge. Which port will become
the root port then? Normally, the lowest Bridge ID is used as the
tiebreaker, but that is not possible in this circumstance.
Port ID is used as the final tiebreaker, and consists of two components:
•4-bit port priority
•12-bit port number, derived from the physical port number

Versions of STP
There are three flavors of the original 802.1D version of STP:
•Common Spanning Tree (CST)
•Per-VLAN Spanning Tree (PVST)
•Per-VLAN Spanning Tree Plus (PVST+)

CST utilizes a single STP instance for all VLANs, and is sometimes
referred to as mono spanning tree. All CST BPDU’s are sent over
the native VLAN on a trunk port, and thus are untagged. PVST
employs a separate STP instance for each VLAN, improving
flexibility and performance. PVST requires trunk ports to use ISL
encapsulation. PVST and CST are not compatible. The enhanced
PVST+ is compatible with both CST and PVST, and supports both
ISL and 802.1Q encapsulation. PVST+ is the default mode on many
Cisco platforms.

STP has continued to evolve over time. Modern extensions of STP

will be covered later in this guide:
•Rapid Spanning Tree Protocol (RSTP)

•Multiple Spanning Tree (MST)

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Basic STP Configuration

STP is enabled by default on all Cisco switches, for all VLANs and
ports. PVST+ is the default STP mode on most modern Cisco
platforms, allowing each VLAN to run a separate STP instance.
STP can be disabled. This should be done with caution - any
switching loop will result in a broadcast storm.

To disable STP for an entire VLAN:

Switch(config)# no spanning-tree vlan 101

A range of VLANs can be specified:

Switch(config)# no spanning-tree vlan 1 – 4094

STP can also be disabled on a per-port basis, for a specific VLAN:

Switch(config)# interface gi2/23
Switch(config-if)# no spanning-tree vlan 101

The switch with the lowest Bridge ID is elected as the Root Bridge.
The priority can be adjusted from its default of 32,768, to increase
the likelihood that a switch is elected as the Root Bridge.
Priority can be configured on a per-VLAN basis. Remember that the
priority must be in multiples of 4,096 when extended system IDs are
enabled: SwitchA(config)# spanning-tree vlan 101 priority 8192

A switch can be indirectly forced to become the Root Bridge for a

specific VLAN:
SwitchA(config)# spanning-tree vlan 101 root primary

The root primary parameter automatically lowers the priority to

24,576. If another switch has a priority lower than 24,576, the
priority will be lowered to 4,096 less than the current Root

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Bridge.

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STP does not technically support a backup Root Bridge. However,

the root secondary command can increase the likelihood that a
specified switch will succeed as the new Root Bridge in the event
of a failure: SwitchB(config)# spanning-tree vlan 101 root
secondary

-tree vlan 101 root secondary

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STP Port States

As STP converges the switching topology, a switch port will

progress through a series of states:

 Blocking

 Listening

 Learning

 Forwarding

Initially, a switch port will start in a blocking state:

-A blocking port will not forward frames or learn MAC addresses.
-A blocking port will still listen for BPDUs from other
switches, to learn about changes to the switching topology.

A port will then transition from a blocking to a listening state:

-The switch must believe that the port will not be shut
down to eliminate a loop. In other words, the port may become
a root or designated port.
-A listening port will not forward frames or learn MAC addresses.
-A listening port will send and listen for BPDUs, to participate
in the election of the Root Bridge, root ports, and designated ports.
-If a listening port is not elected as a root or a designated Port, it will
transition back to a blocking state.

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If a listening port is elected as a root or designated port, it will transition to a

learning state:
-A port must wait a brief period of time, referred to as the
forward delay, before transitioning from a listening to learning state.
-A learning port will continue to send and listen for BPDUs.
-A learning port will begin to add MAC addresses to the CAM table.
-However, a learning port cannot forward frames quite yet.

Finally, a learning port will transition to a forwarding state:

-A port must wait another forward delay before transitioning
from learning to forwarding.
-A forwarding port is fully functional – it will send and
listen for BPDUs, learn MAC addresses, and forward frames.
-Root and designated ports will eventually transition to a forwarding
state.

Technically, there is a fifth port state – disabled. A port in a

disabled state has been administratively shutdown. A disabled
port does not forward frames or participate in STP
convergence.
Why does a port start in a blocking state? STP must initially
assume that a loop exists. A broadcast storm can form in
seconds, and requires physical intervention to stop.

Thus, STP will always take a proactive approach. Starting in a

blocking state allows STP to complete its convergence process
before any traffic is forwarded. In perfect STP operation, a broadcast
storm should never occur.

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- To view the current state of a port:

STP Timers

Switches running STP exchange BPDUs to build and converge the

topology database. There are three timers that are crucial to the
STP process:

-Hello timer

-Forward delay timer

-Max Age timer

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The hello timer determines how often switches send

BPDUs. By default, BPDUs are sent every 2 seconds.

The forward delay timer determines how long a port must spend in
both a learning and listening state:
-Introducing this delay period ensures that STP will have
enough time to detect and eliminate loops.
-By default, the forward delay is 15 seconds.
-Because a port must transition through two forward delays,
the total delay time is 30 seconds.

The max age timer indicates how long a switch will retain BPDU
information from a neighbor switch, before discarding it:
-Remember that BPDUs are sent every two seconds.
-If a switch fails to receive a BPDU from a neighboring
switch for the max age period, it will assume there was a change
in the switching topology.
-STP will then purge that neighbor’s BPDU information.
-By default, the max age timer is 20 seconds.

Timer values can be adjusted. However, this is rarely necessary,

and can negatively impact STP performance and reliability.
Timers must be changed on the Root Bridge. The Root Bridge
will propagate the new timer values to all switches using
BPDUs. Non-root switches will ignore their locally configured
timer values.

To manually adjust the three STP timers for a specific VLAN:

Switch(config)# spanning-tree vlan 101 hello-time 10
Switch(config)# spanning-tree vlan 101 forward-time 20
Switch(config)# spanning-tree vlan 101 max-age 40
The timer values are measured in seconds, and the above
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represents the maximum possible value for each timer.

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- Improving STP Convergence

In many environments, a 30 second outage for every topology

change is unacceptable. Cisco developed three proprietary features
that improve STP convergence time:

 PortFast

 UplinkFast

 BackboneFast
Each feature will be covered in detail in the following sections.

- PortFast

By default, all ports on a switch participate in the STP topology.

This includes any port that connects to a host, such as a
workstation. In most circumstances, a host represents no risk of
a loop.

The host port will transition through the normal STP states,
including waiting two forward delay times. Thus, a host will
be without network connectivity for a minimum of 30
seconds when first powered on.

This is not ideal for a couple reasons:

 Users will be annoyed by the brief outage.

 A host will often request an IP address through DHCP during

bootup. If the switch port is not forwarding quickly enough,
the DHCP request may fail.

 Devices that boot from network may fail as well.

PortFast allows a switch port to bypass the usual progression

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of STP states.

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The port will instead transition from a blocking to a forwarding state

immediately, eliminating the typical 30 second delay.
PortFast should only be enabled on ports connected to a host.
If enabled on a port connecting to a switch or hub, any loop
may result in a broadcast storm.

Note: PortFast does not disable STP on a port - it merely

accelerates STP convergence. If a PortFast-enabled port
receives a BPDU, it will transition through the normal
process of STP states.

PortFast provides an additional benefit. Remember that a

switch will generate a TCN if a port transitions to a
forwarding or blocked state. This is true even if the port
connects to a host device, such as a workstation.
Thus, powering on or off a workstation will cause TCNs to
reach the Root Bridge, which will send out configuration
BPDUs in response. Because the switching topology did

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not technically change, no outage will occur.

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However, all switches will reduce the CAM aging timer to

15 seconds, thus purging MAC addresses from the table
very quickly. This will increase frame flooding and reduce
the efficiency and performance. PortFast eliminates this
unnecessary BPDU traffic and frame flooding. A TCN will
not be generated for state changes on a Port Fast-enabled
port. Portfast is disabled by default.

To enable PortFast on a switch port:

SwitchD(config)# int gi1/14
SwitchD(config-if)# spanning-tree portfast

PortFast can also be globally enabled for all interfaces:

SwitchD(config)# spanning-tree portfast default

- UplinkFast
Often, a switch will have multiple uplinks to another upstream switch:

If the links are not bundled using an EtherChannel, at least one of

the ports will transition to a blocking state to eliminate the loop.

In the above example, port gi2/24 was placed into a blocking

state on SwitchB.
Normally, if the root port fails on the local switch, STP will need
to perform a recalculation to transition the other port out of a
blocking state. At a minimum, this process will take 30 seconds.

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UplinkFast allows a blocking port to be held in a standby state. If

the root port fails, the blocking port can immediately transition to
a forwarding state. Thus, UplinkFast improves convergence time
for direct failures in the STP topology.
If multiple ports are in a blocking state, whichever port has the
lowest root path cost will transition to forwarding.

UplinkFast is disabled by default, and must be enabled globally

for all VLANs on the switch:
Switch(config)# spanning-tree uplinkfast

UplinkFast functions by tracking all possible links to the Root

Bridge. Thus, UplinkFast is not supported on the Root Bridge. In
fact, enabling this feature will automatically increase a switch’s
bridge priority to 49,152.
UplinkFast is intended for the furthest downstream switches in the
STP topology.

- BackboneFast
UplinkFast provides faster convergence if a directly-connected port
fails. In contrast, BackboneFast provides improved convergence if
there is an indirect failure in the STP topology.

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If the link between SwitchB and SwitchA fails, SwitchD will

eventually recalculate a path through SwitchE to reach the Root
Bridge. However, SwitchD must wait the max age timer before
purging SwitchB’s superior BPDU information. By default, this is
20 seconds.

BackboneFast allows a switch to bypass the max age timer. The

switch will accept SwitchE’s inferior BPDU’s immediately. The
blocked port on SwitchE must still transition to a forwarding
state. Thus, BackboneFast
essentially reduces total convergence time from 50 seconds to 30
seconds for an indirect failure.

This is accomplished by sending out Root Link Queries (RLQs). The

Root Bridge will respond to these queries with a RLQ Reply:

 If a RLQ Reply is received on a root port, the switch knows

that the root path is stable.

 If a RLQ Reply is received on a non-root port, the switch

knows that the root path has failed. The max age timer is
immediately expired to allow a new root port to be elected.

BackboneFast is a global command, and should be enabled on

every switch:
Switch(config)# spanning-tree backbonefast

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Troubleshoot

Troubleshoot a Failure

Unfortunately, there is no systematic procedure to troubleshoot an

STP issue. However, this section sums up some of the actions that
are available. Most of the steps in this section apply to the
troubleshooting of bridging loops in general. We can use a more
conventional approach to identify other failures of the STP that lead
to a loss of connectivity. For example, we can explore the path that
the traffic that experiences a problem takes.

Note: Most of these troubleshooting steps assume connectivity to

the different devices of the bridge network. This connectivity means
you having a console access.

Use the Diagram of the Network

Before we troubleshoot a bridging loop, we need to know these

items, at minimum:

 The topology of the bridge network

 The location of the root bridge

 The location of the blocked ports and the redundant links

This knowledge is essential for at least these two reasons:

 In order to know what to fix in the network, we need to

know how the network looks when it works correctly.

 Most of the troubleshooting steps simply use show

commands to try to identify error conditions. Knowledge of
the network helps us focus on the critical ports on the key
devices.

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Identify a Bridging Loop

It used to be that a broadcast storm could have a disastrous effect

on the network. Today, with high-speed links and devices that
provide switching at the hardware level, it is not likely that a single
host, for example, a server, brings down a network through
broadcasts. The best way to identify a bridging loop is to capture
the traffic on a saturated link and check that you see similar packets
multiple times. Realistically, however, if all users in a certain bridge
domain have connectivity issues at the same time, we can already
suspect a bridging loop.

On the Catalyst switches that run CatOS, we can easily check the
overall backplane usage with the show system command. The
command provides the current usage of the switch backplane and
also specifies the peak usage and date of peak usage. An unusual
peak utilization shows us whether there has ever been a bridging
loop on this device.

Log STP Events on Devices That Host Blocked Ports

If we cannot precisely identify the source of the problem, or if the

problem is transient, enable the logging of STP events on the
bridges and switches of the network that experiences the failure. If
we want to limit the number of devices to configure, at least enable
this logging on devices that host blocked ports; the transition of a
blocked port is what creates a loop.

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Debug spanning-tree

 Cisco IOS Software-Issue the exec command debug spanning-

tree events to enable STP debug information. Issue the
general config mode command logging buffered to capture
this debug information in the device buffers.

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Show spanning-tree

 Cisco IOS Software-In Cisco IOS Software Release 12.0 or

later, output of the show spanning-tree bridge-group #
command has
a BPDU field. The field shows you the number of BPDUs
received for each interface. Issue the command an additional
one or two times to determine if the device receives BPDUs.

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Show spanning-tree summary totals

 Issue the show spanning-tree summary totals command for

switches that run Cisco IOS Software. These commands
display the number of logical ports or interfaces per VLAN
in the STP
Active column.

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Chapter6:
Conclusion
Finally we made the network and we can divide the network to
4 main sections:

1- We decided that we will use packet tracer then transfer the

design to GNS3 & VMware to emulate and test the network.

2- EtherChannel: we designed and used it then configured it

after that we tested it to make sure that all configurations work.

3- Load-Balancing & redundancy: we designed the network and

setup GLBP protocol to make the campus network load-balanced
and available all time then we tested it to be sure that the network
working correctly.

4- STP: Finally we use this protocol to ensure that we do not

create loops when we have redundant paths in our network.
Loops are deadly to a network.

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This is the final network

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Appendices
Value Description

IP Internet Protocol version 4

STP Spanning Tree protocol

BPDU Bridge Protocol Data Unit

PAgP Port Aggregation Protocol

LACP Link Aggregation Control

Protocol

BPDU Bridge Protocol Data Units

RSTP Rapid Spanning Tree Protocol

MST Multiple Spanning Tree

GLBP Gateway Load Balancing Protocol

VRRP Virtual Router Redundancy

Protocol

HSRP Hot Standby Router Protocol

VLAN virtual LAN

MAC address Media Access Control address

ISL Inter-Switch Link

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References
 https://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/
ft_glbp.html#wp1048594

 https://www.cisco.com/c/en/us/support/docs/lan-
switching/spanning-tree-protocol/5234-5.html

 https://www.cisco.com/en/US/docs/ios/12_2/switch/configuration/g
uide/xcfmsc_external_docbase_0900e4b180753c28_4container_ext
ernal_docbase_0900e4b18088695e.html

 https://www.cisco.com/c/en/us/support/docs/lan-
switching/etherchannel/12023-4.html

 Books About : -Redundancy and Load Balancing

- Spanning Tree Protocol

- EtherChannel

-Multilayer Switching

From: http://www.routeralley.com. By Aaron Balchunas.

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