Transcript ITEC 275 Computer Networks * Switching, Routing, and WANs

ITEC 275
Computer Networks – Switching, Routing, and
WANs
Week 3
Robert D’Andrea
Winter 2016
Agenda
• Review
• Learning Activities
– Analyzing an Existing Network
– Analyzing Traffic in an Existing Network
– QoS
• Introduce homework problems
What’s the Starting Point?
• According to Abraham Lincoln:
– “If we could first know where we are and
whither we are tending, we could better judge
what to do and how to do it.”
Where Are We?
When we characterize the infrastructure of a
network, we develop a set of network maps and locate
major devices and network segments.
Developing a network map should involve
understanding traffic flow, performance characteristics
of network segments, and insight into where the users
are concentrated and the level of traffic a network
design must support. Everything you can think of to
understand your customers network.
Where Are We?
When characterizing our network, we eventually
want to visualize the whole infrastructure, but not at
the same time. This is done by the use of layering of
graphics displays.
Layers are simultaneous, over lapping
components of an image or sequence. They are at work
in many media software programs from Photoshop and
Illustrator to audio, video, and animation tools, where
multiple layers of image and sound (tracks) unfold in
time.
Where Are We?
The concept of layers comes from the
physical world, and it has a long history in the
traditions of mapping and musical notation. Maps
and time lines use overlapping layers to associate
different levels of data, allowing them to
contribute to the whole while maintaining their
own identities.
Where Are We?
Developing an understanding of your
customers existing network’s structure, involves
it’s uses, and behavior, then you have a better
chance of determining if you’re design goals are
realistic.
Where Are We?
• Characterize the existing internetwork in terms
of:
– Its infrastructure
• Logical structure (modularity, hierarchy, topology)
• Physical structure
– Addressing and naming
– Wiring and media
– Architectural and environmental constraints
– Over all health of their network
How to Start?
• Characterization should start by using a topdown approach.
– Starting with a map or set of maps depicting a
high-level abstraction of information
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Geographical information
WAN
WAN to LAN
Buildings, floors, and wiring within the building
Rooms containing servers, routers, mainframes, and
switches
• Virtual information
How to Start?
• Characterizing large complex networks should reflect
influence from the OSI reference model.
• A network map should depict applications and
services used by the network users.
Internal and external web sites
Email and external data access entries
Ftp operations
Printer and file sharing devices
DHCP, DNS, SNMP
Router interface names, firewalls, NAT, IDS, and
IPS
How to Start?
Use tools that automate diagram representation of the
network.
IBM’s Tivoli
What’s Up Gold from ipswitch
LAN surveyor
Microsoft Visio Professional
Network Map
Medford
Fast Ethernet
50 users
Roseburg
Fast Ethernet
30 users
Frame Relay
CIR = 56 Kbps
DLCI = 5
Frame Relay
CIR = 56 Kbps
DLCI = 4
Grants Pass
HQ
Gigabit
Ethernet
Gigabit
Ethernet
Grants Pass
HQ
Fast Ethernet
75 users
FEP
(Front End
Processor)
IBM
Mainframe
T1
Web/FTP server
Eugene
Ethernet
20 users
T1
Internet
Characterize Large Internetworks
Developing one map might be difficult to do
for a large internetwork. Many approaches might
be needed for dissecting and understanding the
problem.
• Apply a top-down method influenced by the OSI
reference model
• Develop a series of maps (high (high level of
abstraction) to low level)
• Develop a logical map (shows applications, and
services used by network users)
Characterize Large Internetworks
Develop a map of internal server functions:
Web
Email
sftp
Printing
File sharing
Characterize Large Internetworks
Develop a map of external server functions:
Web
Email
sftp
Mobile
Web caching servers on your map
must be identified because they can affect your
traffic flow.
Characterize Large Internetworks
Develop a map of network services:
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Terminal Access Controller Access Control
System (TACACS) server(s)
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Remote Authentication Dial-In User
Service (RADIUS) server(s)
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Dynamic Host Configuration Protocol
(DHCP)
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Domain Name System (DNS)
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Simple Network Management Protocol
(SNMP)
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Location and reach of virtual private
networks (VPN)
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Dial-in and dial-out servers
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WAN
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Internet
Characterize Large Internetworks
Develop a map of network services:
• Layer 3 topology of the internetwork (Cisco notation
s0/0 ). This layer of information may reflect a network
of devices from a single vendor or a mix of vendors.
• Protocols
• Firewalls
• NAT (Network Address Translation)
• IDS (Intrusion Detection System)
• IPS (Intrusion Prevention Detection)
• Layer 2 devices
• LAN devices and interfaces
• Public and private WAMs
Characterize a Logical Architecture
• Determine the logical topology of the network. Is the
network flat, hierarchical, structured or unstructured,
layered or not.
• Geometric shape of network (star, spoke, ring, or
mesh)
• Look for ticking time bombs that could affect
scalability. These are large layer 2 Spanning Tree
Protocol (STP) domains that take excessive time to
converge.
• Flat topologies do not scale as well as hierarchical
topologies. This affects the ability to upgrade the
network.
Flat Network
Characterize a Logical Architecture
Enterprise Campus
Characterize a Logical Architecture
Enterprise Edge
Characterize Addressing and Naming
• IP addressing for major network devices, client,
server, and private.
• Any addressing oddities, such as discontinuous
subnets?
• Any strategies for addressing and naming?
– Route summarization reduces routes in a router
– For example, sites may be named using airport
codes
• San Francisco = SFO, Oakland = OAK
Networks Names
What is a network name?
A network name is a text string that devices
use to reference a particular computer network.
These strings are, strictly speaking, separate from
the names of individual devices and the addresses
they use to identify each other.
Networks Names
What is a network name?
Wi-Fi networks support a type of network
name called SSID. Wi-Fi access points and clients
are each always assigned an SSID to help identify
each other. When a person speaks of wireless
network names, they typically are referring to
SSIDs.
Microsoft Windows supports assigning PCs
to named workgroups to facilitate peer-to-peer
networking.
Networks Names
Alternatively, Windows domains can be
used to segregate PCs into named sub-networks.
Both Windows workgroup and domain names are
set separately from the names of each PC and also
function independently from SSIDs.
Yet another distinct form of network naming
is sometimes used to identify computer clusters.
Most server operating systems, for example, such
as Microsoft Windows Server support
independent naming of clusters.
Characterize Addressing and Naming
• Route summarization reduces routes in a
routing table, routing-table update traffic,
and overall router overhead. Route
summarization improves network stability
and availability, because problems in one
area of the network are less likely to affect
the whole network.
• Dis-contiguous subnet is a subnet that has
been divided into two areas.
Route Summarization
Dis-contiguous Subnets
Area 0
Network
192.168.49.0
Router A
Router B
Area 1
Subnets 10.108.16.0 -
Area 2
Subnets 10.108.32.0 -
10.108.31.0
10.108.47.0
Characterize Addressing and Naming
• Network addressing scheme might affect the routing
protocols. Some routing protocols do not support
Classless addressing
Variable-length subnet masking (VLSM)
Discontiguous subnets - Discontiguous subnets
are really a major issue when it comes to classful
routing protocols or trying to achieve intelligent
summarization across your network. Otherwise, most
major routing protocols can adapt to them - it just
results in a larger routing table.
Characterize the Wiring and Media
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Single-mode fiber
Multi-mode fiber
Shielded twisted pair (STP) copper
Unshielded-twisted-pair (UTP) copper
Coaxial cable
Microwave
Laser
Radio
Infra-red
Characterize the Wiring and Media
Distance information is critical when
selecting data link layer technologies.
It is helpful knowing how much copper
cable might need to be replaced if fiber cabling
is to be used and if there is access for the
replacement.
Determine the type of wiring used
between the wiring closet, cross-connect
rooms, and computer rooms.
Characterize the Wiring and Media
Vertical wiring run between floors of a
building
Horizontal wiring run from the wiring
closet to the wall plate in the office cubicles.
Work-area wiring runs from the wall
plate to the workstation.in a cubicle.
Generally, the distance from the wiring
closet to the workstation are approximately 100
meters.
Characterize the Wiring and Media
Characterize the Wiring and Media
Cable Standards and Connectors:
The larger the number, the better the
protection from interference. Most networks
utilize nothing less than CAT5 or CAT6 or
CAT6a.
The connector that cousin to the phone
jack is the RJ-45. The RJ-45 connection looks
similar but is larger in size.
Characterize the Wiring and Media
Characterize the Wiring and Media
CAT 5 10/100 BaseT RJ-45
Characterize the Wiring and Media
Fiber Optic connectors
Campus Network Wiring
Horizontal
Wiring
Work-Area
Wiring
Wallplate
Telecommunications
Wiring Closet
Vertical
Wiring
(Building
Backbone)
Main Cross-Connect Room
(or Main Distribution Frame)
Building A - Headquarters
Intermediate Cross-Connect Room
(or Intermediate Distribution Frame)
Campus
Backbone
Building B
Characterize the Wiring and Media
A time-domain reflectometer (TDR) is
used to determine the distance of a cable. It is
an electronic instrument that uses timedomain reflective technology to characterize
and locate faults in metallic cables (for
example, twisted-pair cable or coaxial cable)
Characterize the Wiring and Media
TDR
Architectural Constraints
• Make sure the following are sufficient
– Air conditioning
– Heating
– Ventilation
– Electrical power
– Protection from electromagnetic interference
– Door locking mechanism
– Environmental issues
– Too close to a right-of-way
Architectural Constraints
Parameter
Copper Twisted Pair
MM Fiber
SM Fiber
Wireless
Distance
Up to 100 meters
Up to 2 kilometers (Fast
Ethernet)
Up to 550 m (Gigabit
Ethernet)
Up to 300 m (10 Gigabit
Ethernet)
Up to 10 km (Fast
Up to 500 m at 1 Mbps
Ethernet)
Up to 5 km (Gigabit
Ethernet)
Up to 80 km (10 Gigabit
Ethernet)
Bandwidth
Up to 10 Gigabits per
second (Gbps)
Up to 10 Gbps
Up to 10 Gbps or higher Up to 54 Mbps
Price
Inexpensive
Moderate
Moderate to expensive Moderate
Deployment
Wiring closet
Internode or
interbuilding
Internode or
interbuilding
Internode or
interbuilding
Architectural Constraints
• Make sure there’s space for:
– Cabling conduits
– Patch panels
– Equipment racks
– Work areas for technicians to install and
troubleshooting equipment
Wireless Installation
• Inspect the architecture and environment
constraints of the site to determining the
feasibility of a wireless transmission.
– Wireless transmission is RF (radio frequency)
– A wireless expert should be hired
– Network designers can install access point(s) where
people tend to concentrate
– Signal loss occurs between the access point and the
user of the access point.
Wireless Installation
• A wireless site survey is used to describe the
process of evaluating the a site to see if it will
be appropriate for wireless transmission.
• An access point is likely to be placed in a
location based on an estimate of signal loss that
will occur between the access point and the
users of the WLAN. An access point is a device
that transmits and receives data for users on a
WLAN. Generally, it is a point on
interconnection between the WLAN and wired
Ethernet network.
RF Phenomena Wireless Installations
1. Reflection causes the signal to bounce back on
itself.
2. Absorption occurs as the signal passes through
materials
3. Refraction is when a signal passes through one
medium of one density and then through another
medium of another density. Signal will bend.
4. Diffraction when a signal can pass in part
through a medium more easily in one part than another
RF Phenomena Wireless Installations
1. Reflection signal causes the signal to bounce
back on itself. The signal can interfere with itself
in the air and affect the receiver’s ability to
discriminate between the signal and noise in the
environment. Reflection is caused by metal
surfaces such as steel girders, scaffolding,
shelving units, steel pillars, and metal doors.
Implementing a Wireless LAN (WLAN) across a
parking lot can be tricky because of metal cars
that come and go.
Reflective Wireless Signal
Reflective Wireless Signal
Reflective Wireless Signal
RF Phenomena Wireless Installations
2. Some of the electromagnetic energy of the signal can
be absorbed by the material in objects through which it
passes, resulting in a reduced signal level. Water has
significant absorption properties, and objects such as
trees or thick wooden structures can have a high water
content. Implementing a WLAN in a coffee shop can be
tricky if there are large canisters of liquid coffee. Coffeeshop WLAN users have also noticed that people coming
and going can affect the signal level. (On StarTrek, a
non-human character once called a human “an ugly giant
bag of mostly water”!)
Absorption Wireless Signal
RF Phenomena Wireless Installations
3. Refraction is when an RF signal passes from a medium
with one density into a medium with another density, the
signal can be bent, much like light passing through a
prism. The signal changes direction and may interfere
with the non-refracted signal. It can take a different path
and encounter other, unexpected obstructions, and arrive
at recipients damaged or later than expected. As an
example, a water tank not only introduces absorption, but
the difference in density between the atmosphere and the
water can bend the RF signal.
Reflective Wireless Signal
RF Phenomena Wireless Installations
4. Diffraction, which is similar to refraction,
results when a region through which the RF signal
can pass easily is adjacent to a region in which
reflective obstructions exist. So, a signal can pass
in part through a medium more easily in one part
than another. Like refraction, the RF signal is bent
around the edge of the diffractive region and can
then interfere with that part of the RF signal that
is not bent.
Diffraction Wireless Signal
RF Phenomena Wireless Installations
• A wireless Site Survey should be performed on
the existing network for signal propagation,
strength, and accuracy in different areas.
– NIC cards ship with utilities on them to measure
signal strength
– Signal strength can be determined using a protocol
analyzer
– Access points send beacon frames every 100
milliseconds (ms). Use a protocol analyzer to
analyze the signal strength being emitted from the
different grid locations of the access points.
RF Phenomena Wireless Installations
- Use a protocol analyzer to capture CRC
errors. These errors stem from
corruption and collisions.
- Observe if frames are being lost in
transmission
- Observe if acknowledgment (ACK) and
frame retries after a missing ACK.
ACK is called a control frame. Clients
and access points use them to
implement a retransmission mechanism
RF Phenomena Wireless Installations
• Wired Ethernet
Detects collisions through CSMA/CD
(802.11)
Ethernet uses CSMA/CA as the access
method to gain access of the wire. An ACK
control frame is returned to a sender for
packet received. If a frame does not
receive an ACK, it is retransmitted.
Check the Health of the Existing
Internetwork
• Baseline network performance with sufficient time and at a
typical time
• Baseline availability gather information from the customer
on MTBF and MTTR
• Baseline bandwidth utilization during a specific time frame.
This is usually a percentage of capacity.
• Accuracy is an upper layer protocol’s responsibility. A
frame with a bad CRC is dropped and retransmitted. A good
threshold rule for handling errors is that there should be no
more than one bad frame per megabyte of data.
Check the Health of the Existing
Internetwork
Accuracy is a measurement of lost packets.
This measurement is achieved by keeping track of
lost packets while measuring response time.
-Switches have replaced hubs.
- There should be fewer than 0.1
percent of frames encounter collisions.
- There should be no late collisions. Indicate
bad cabling, cabling longer than
100 meters,
bad NIC, or duplex mismatch.
Check the Health of the Existing
Internetwork
Auto-negotiation has received it’s share
of criticism in the past for being inaccurate
when setting up a point-to-point link half
duplex and full duplex.
Auto-negotiation of speed is usually not a
problem. If set up incorrectly, it does not work.
The speeds are 10 Mbps, 100 Mbps, or 1000
Mbps.
Check the Health of the Existing
Internetwork
Category 3 cable will support 10MBps, but not
100 MBps and higher. Errors increase.
• Efficiency is linked to large frame sizes. Bandwidth
utilization is optimized for efficiency when
applications and protocols are in large sized frames.
– Change window sizes on clients and servers. Increasing
maximum transmission unit (MTU).
– Able to ping and telnet but not be able to send HTTP, and
FTP.
– A hump exist on the sides of the average transmission.
– Runt frames (less than 64 bytes) are a result of collisions
on the same shared Ethernet segment.
Check the Health of the Existing
Internetwork
• Response time can be measured using the
round-trip time (RTT) ping command.
Observe response time on a user
workstation. Run typical applications to
get a response.
Response time for network services
protocols, such as, DHCP and DNS.
• Status of major routers, switches, and
firewalls
Characterize Availability
MTBF
Enterprise
Segment 1
Segment 2
Segment n
MTTR
Date and Duration of Cause of Last
Major
Last Major
Downtime
Downtime
Fix for Last
Major
Downtime
Network Utilization in Minute Intervals
Network Utilization
Utilization
16:40:00
16:42:00
16:44:00
16:46:00
16:48:00
16:50:00
Time
16:52:00
16:54:00
Series1
16:56:00
16:58:00
17:00:00
17:02:00
17:04:00
17:06:00
17:08:00
17:10:00
0.
1.75
3.5
5.25
7.
Network Utilization in Hour Intervals
Network Utilization
Utilization
13:00:00
Time
14:00:00
15:00:00
Series1
0.666667
17:00:00
0.
1.
2.
3.
4.
5.
Bandwidth Utilization by Protocol
Relative
Network
Utilization
Protocol 1
Protocol 2
Protocol 3
Protocol n
Absolute
Network
Utilization
Broadcast Rate
Multicast Rate
Characterize Packet Sizes
Characterize Response Time
Node A
Node A
Node B
Node C
Node D
Node B
Node C
Node D
X
X
X
X
Check the Status of Major Routers,
Switches, and Firewalls
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Show buffers
Show environment
Show interfaces
Show memory
Show processes
Show running-config
Show version
Check the Status of Major Routers,
Switches, Hubs, and Firewalls
Hubs (bit cloning machine)
Span every connection on a hub
Cheap
Wasteful of bandwidth
Sends replicated packet data on all ports
When monitoring (Wireshark) a network,
see redundant traffic
Check the Status of Major Routers, Switches,
and Firewalls
Switches
Less complicated than routers
Used for Ethernet and Wi-Fi medium based on
MAC address (burnt on NIC)
Initially, a switch table is empty. Broadcasts on all
ports until all port connections are discovered.
Switch uplink port can be used to connect to
router(s).
Switches deliver packets directly to the correct
destination without spanning all port connections.
Check the Status of Major Routers,
Switches, and Firewalls
Switch table
Interface
MAC Addresses
1
AA-AA-AA-AA-AA-AA
2
CC-CC-CC-CC-CC-CC
3
DD-DD-DD-DD-DD-DD
Check the Status of Major Routers,
Switches, and Firewalls
Router
Routers connect networks
Support NAT and DHCP
Utilize the IP protocol
Internal Ethernet switch built-in
Check the Status of Major Routers,
Switches, and Firewalls
Hubs, Switches, and Routers
Each of these devices operates at a different
layer.
Network
Link
Physical
IP protocol
194.78.0.163
Medium over which the packet is traveling.
Ethernet and Wi-Fi . MAC Address
01-DE-89-0A-77-BB
Raw 01001000111100…
Tools
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Protocol analyzers
Multi Router Traffic Grapher (MRTG)
Remote monitoring (RMON) probes
Cisco Discovery Protocol (CDP)
Cisco IOS NetFlow technology
CiscoWorks
Network Traffic Factors
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Traffic flow
Location of traffic sources and data stores
Traffic load
Traffic behavior
Quality of Service (QoS) requirements
User Communities
User Community
Name
Size of
Community
(Number of
Users)
Location(s) of
Community
Application(s)
Used by
Community
Data Stores
Data Store
Location
Application(s)
Used by User
Community(or
Communities)
Traffic Flow
Destination 1
MB/sec
Source 1
Source 2
Source 3
Source n
Destination 2
MB/sec
Destination 3
MB/sec
Destination
MB/sec
Library and Computing Center
Traffic Flow
Example
App 2
App 3
App 4
App 9
Total
20
96
24
80
220
30 Library Patrons (PCs)
30 Macs and 60 PCs in
Computing Center
Server Farm
Kbps
Kbps
Kbps
Kbps
Kbps
10-Mbps Metro
Ethernet to Internet
App 1
App 2
App 3
App 4
App 7
Total
108
60
192
48
400
808
Kbps
Kbps
Kbps
Kbps
Kbps
Kbps
25 Macs
50 PCs
50 PCs
Arts and
Humanities
Administration
App 1
App 2
App 3
App 4
Total
30 PCs
Business and Social
Sciences
30
20
60
16
126
Kbps
Kbps
Kbps
Kbps
Kbps
App 1
48 Kbps
App 2
32 Kbps
App 3
96 Kbps
App 4
24 Kbps
App 5 300 Kbps
App 6 200 Kbps
App 8 1200 Kbps
Total 1900 Kbps
Math and
Sciences
50 PCs
Types of Traffic Flow
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Terminal/host
Client/server
Thin client
Peer-to-peer
Server/server
Distributed computing
Traffic Flow for Voice over IP
• The flow associated with transmitting the
audio voice is separate from the flows
associated with call setup and teardown.
– The flow for transmitting the digital voice is
essentially peer-to-peer.
– Call setup and teardown is a client/server flow
• A phone needs to talk to a server or phone
switch that understands phone numbers, IP
addresses, capabilities negotiation, and so
on.
Network Applications
Traffic Characteristics
Name of
Application
Type of
Traffic Flow
Protocol(s)
Used by
Application
User CommunitiesData Stores
That Use the
(Servers, Hosts,
Application
and so on)
Approximate
Bandwidth
Requirements
QoS
Requirements
Traffic Load
• To calculate whether capacity is sufficient, you
should know:
– The number of stations
– The average time that a station is idle between sending
frames
– The time required to transmit a message once medium
access is gained
• That level of detailed information can be hard to
gather, however.
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Size of Objects on Networks
Terminal screen: 4 Kbytes
Simple e-mail: 10 Kbytes
Simple web page: 50 Kbytes
High-quality image: 50,000 Kbytes
Database backup: 1,000,000 Kbytes or more
Traffic Behavior
• Broadcasts
– All ones data-link layer destination address
• FF: FF: FF: FF: FF: FF
– Doesn’t necessarily use huge amounts of bandwidth
– But does disturb every CPU in the broadcast domain
• Multicasts
– First bit sent is a one
• 01:00:0C:CC:CC:CC (Cisco Discovery Protocol)
– Should just disturb NICs that have registered to receive it
– Requires multicast routing protocol on internetworks
Network Efficiency
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Frame size
Protocol interaction
Windowing and flow control
Error-recovery mechanisms
Network Efficiency
Network utilization is the measurement of the
amount of bandwidth that is used during a specific time
interval. The measure is expressed in terms of percentage
of capacity. Seventy percent (70%) is considered a
reasonable level for normal link traffic.
QoS Requirements
• ATM service specifications
– Constant bit rate (CBR)
– Realtime variable bit rate (rt-VBR)
– Non-realtime variable bit rate (nrt-VBR)
– Unspecified bit rate (UBR)
– Available bit rate (ABR)
– Guaranteed frame rate (GFR)
QoS Requirements per IETF
Internet Engineering Task Force (IETF)
• IETF integrated services working group
specifications
– Controlled load service
• Provides client data flow with a QoS closely
approximating the QoS that same flow would receive on
an unloaded network
– Guaranteed service
• Provides firm (mathematically provable) bounds on endto-end packet-queuing delays
QoS Requirements per IETF
• IETF Differentiated Services working group
specifications
• RFC 2475
– IP packets can be marked with a Differentiated
Services Code Point (DSCP) to influence queuing
and packet-dropping decisions for IP datagrams on
an output interface of a router.
Summary
• Characterize the existing internetwork before
designing enhancements.
• Helps you verify that a customer’s design goals are
realistic.
• Helps you locate where new equipment will be
placed.
• Helps you cover yourself if the new network has
problems due to unresolved problems in the old
network.
Summary
• Continue to use a systematic, top-down
approach
• Don’t select products until you understand
network traffic in terms of:
– Flow
– Load
– Behavior
– QoS requirements
Review Questions
• What factors will help you decide if the existing
internetwork is in good enough shape to support new
enhancements?
• When considering protocol behavior, what is the
difference between relative network utilization and
absolute network utilization?
• Why should you characterize the logical structure of
an internetwork and not just the physical structure?
• What architectural and environmental factors should
you consider for a new wireless installation?
Review Questions
• List and describe six different types of traffic flows.
• What makes traffic flow in voice over IP networks
challenging to characterize and plan for?
• Why should you be concerned about broadcast traffic?
• How do ATM and IETF specifications for QoS differ?
This Week’s Outcomes
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Characterize the Existing Network
Analyzing Traffic in an Existing Network
Determine QoS
Wireless Signals
Due this week
• 2-1 – Concept questions 2
Next week
• 3-1 – Concept questions 3
• FranklinLive session 4
• Ensure you have the VMware View Client
installed
• Examine the MIMIC simulator software
Q&A
• Questions, comments, concerns?