ITEC 275 Computer Networks – Switching, Routing, and WANs

ITEC 275 Computer Networks – Switching, Routing, and WANs
Accuracy is a measurement of lost packets. This measurement is achieved by keeping track of lost packets while measuring response time. Week 3 Robert D’Andrea Some slides provide by Priscilla Oppenheimer and used with permission

Agenda Review Learning Activities Introduce homework problems
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? 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 Health

How to Start? Characterization can start by using a top-down approach.
Starting with a map or set of maps depicting a high-level abstraction of information Geographical information WAN WAN to LAN Buildings and floors 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 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

Get a Network Map Gigabit Ethernet Frame Relay CIR = 56 Kbps DLCI = 5
Medford Fast Ethernet 50 users Roseburg Fast Ethernet 30 users Frame Relay CIR = 56 Kbps DLCI = 5 Frame Relay CIR = 56 Kbps DLCI = 4 Gigabit Ethernet Grants Pass HQ 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 to low level) Develop a logical map (shows applications, and services used by network users)

Develop a map of internal server functions: Web locations sftp Printing File sharing

Develop a map of external server functions: Web sftp Mobile Web caching servers on your map must be identified because they can affect your traffic flow.

Develop a map of network services: Terminal Access Controller Access Control System (TACACS) server(s) Remote Authentication Dial-In User Service (RADIUS) server(s) Dynamic Host Configuration Protocol (DHCP) Domain Name System (DNS) Simple Network Management Protocol (SNMP) Location and reach of virtual private networks (VPN) Dial-in and dial-out servers WAN Internet

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 IDS IPS 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 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.

Characterize a Logical Architecture Enterprise Campus

Characterize a Logical Architecture Enterprise Edge

Characterize Addressing and Naming
IP addressing for major devices, client networks, server networks, private needing translation, and so on 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

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.

Network addressing scheme might affect the routing protocols. Some routing protocols do not support Classless addressing Variable-length subnet masking (VLSM) Dis-contiguous subnets

Dis-contiguous Subnets
Area 0 Network Router A Router B Area 1 Subnets Area 2 Subnets

Characterize the Wiring and Media
Single-mode fiber Multi-mode fiber Shielded twisted pair (STP) copper Unshielded-twisted-pair (UTP) copper Coaxial cable Microwave Laser Radio Infra-red

Topologies: Hubs, Switches, and routers

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.

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.

A time-domain reflectometer (TDR) is used to determine the distance of a cable. It is an electronic instrument that uses time-domain reflective technology to characterize and locate faults in metallic cables (for example, twisted-pair cable or coaxial cable)

TDR

Campus Network Wiring Building A - Headquarters Building B
Telecommunications Wiring Closet Horizontal Wiring Work-Area Wallplate Main Cross-Connect Room (or Main Distribution Frame) Intermediate Cross-Connect Room (or Intermediate Distribution Frame) Building A - Headquarters Building B Vertical (Building Backbone) Campus Backbone

Architectural Constraints
Make sure the following are sufficient Air conditioning Heating Ventilation Power Protection from electromagnetic interference Doors that can lock Environmental issues Too close to a right-of-way

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 Ethernet) Up to 5 km (Gigabit Ethernet) Up to 80 km (10 Gigabit Ethernet) Up to 500 m at 1 Mbps 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 Deployment Wiring closet Internode or interbuilding

Make sure there’s space for: Cabling conduits Patch panels Equipment racks Work areas for technicians installing 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 points will be located and where the people concentration will be located Access point is based on signal loss 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
Reflection causes the signal to bounce back on itself. Absorption occurs as the signal passes through materials Refraction is when a signal passes through one medium of one density and then through another medium of another density. Signal will bend. Diffraction when a signal can pass in part through a medium more easily in one part than another Reflection. Reflection 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. Absorption. 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. Coffee-shop 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”!) Refraction. 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. Diffraction. 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. 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.

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. Reflection. Reflection 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. Absorption. 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. Coffee-shop 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”!) Refraction. 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. Diffraction. 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. 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.

- Use a protocol analyzer to capture CRC errors. These errors stem from corruption and collisions. - Observe if frames are being lost in transmission - Observe the 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 Reflection. Reflection 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. Absorption. 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. Coffee-shop 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”!) Refraction. 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. Diffraction. 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. 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.

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. Reflection. Reflection 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. Absorption. 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. Coffee-shop 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”!) Refraction. 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. Diffraction. 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. 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.

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.

-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 percent of frames encounter collisions. - There should be no late collisions. Indicate bad cabling, cabling longer than 100 meters, bad NIC, or duplex mismatch.

- 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.

- 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.

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
Cause of Last Major Downtime Date and Duration of Last Major Downtime Fix for Last Major Downtime MTBF MTTR Enterprise Segment 1 Segment 2 Segment n

Network Utilization in Minute Intervals

Network Utilization in Hour Intervals

Bandwidth Utilization by Protocol
Relative Network Utilization Absolute Network Utilization Broadcast Rate Multicast Rate Protocol 1 Protocol 2 Protocol 3 Protocol n Relative usage specifies how much bandwidth is used by the protocol in comparison to the total bandwidth currently in use on the segment. Absolute usage specifies how much bandwidth is used by the protocol in comparison to the total capacity of the segment (for example, in comparison to 100 Mbps on Fast Ethernet).

Characterize Packet Sizes

Characterize Response Time
Node A Node B Node C Node D Node A Node B Node C Node D X X X X

Check the Status of Major Routers, Switches, and Firewalls
Show buffers Show environment Show interfaces Show memory Show processes Show running-config Show version

Tools Protocol analyzers Multi Router Traffic Grapher (MRTG)
Remote monitoring (RMON) probes Cisco Discovery Protocol (CDP) Cisco IOS NetFlow technology CiscoWorks

Network Traffic Factors
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 Destination 2 Destination 3 Destination MB/sec MB/sec MB/sec MB/sec Source 1 Source 2 Source 3 Source n

Library and Computing Center Business and Social Sciences
Traffic Flow Example Library and Computing Center 10-Mbps Metro Ethernet to Internet 30 Library Patrons (PCs) 30 Macs and 60 PCs in Computing Center App Kbps App Kbps App Kbps App Kbps App Kbps Total 808 Kbps Server Farm App Kbps App Kbps App Kbps App Kbps Total 220 Kbps 25 Macs 50 PCs 50 PCs Arts and Humanities Administration App Kbps App Kbps App Kbps App Kbps Total 126 Kbps App Kbps App Kbps App Kbps App Kbps App Kbps App Kbps App Kbps Total 1900 Kbps Math and Sciences 30 PCs 50 PCs Business and Social Sciences

Types of Traffic Flow 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 Communities That Use the Application Data Stores (Servers, Hosts, 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.

Size of Objects on Networks
Terminal screen: 4 Kbytes Simple 10 Kbytes Simple web page: 50 Kbytes High-quality image: 50,000 Kbytes Database backup: 1,000,000 Kbytes or more

Traffic Behavior Broadcasts Multicasts
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 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
IETF (Internet Engineering Task Force) 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 end-to-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 Analyzing an Existing Network
Analyzing Traffic in an Existing Network QoS

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?

ITEC 275 Computer Networks – Switching, Routing, and WANs

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