Analyzing Network Infrastructure for Effective Redesign
Characterizing and mapping an existing network is crucial for determining redesign goals. This involves understanding traffic flow, performance, user concentration, addressing, and naming. By starting with a high-level abstraction, such as geographical and virtual information, you can systematically evaluate the network's logical and physical structures. Considerations like modularity, hierarchy, topology, wiring, architectural constraints, and overall network health are key in this analysis process.
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Presentation Transcript
ITEC 275 Computer Networks Switching, Routing, and WANs Week 3 Robert D Andrea 2015
Agenda Review Learning Activities Analyzing an Existing Network Analyzing Traffic in an Existing Network QoS Introduce homework problems
Whats 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 Over all health of their network
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, 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
Get a 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: 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
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 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 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
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.
Dis-contiguous Subnets Area 0 Network 192.168.49.0 Router A Router B Area 1 Area 2 Subnets 10.108.16.0 - 10.108.31.0 Subnets 10.108.32.0 - 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) Dis-contiguous 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
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.
Campus Network Wiring Horizontal Wiring Work-Area Wiring Wallplate Telecommunications Wiring Closet Vertical Wiring (Building Backbone) Main Cross-Connect Room (or Main Distribution Frame) Intermediate Cross-Connect Room (or Intermediate Distribution Frame) Campus Backbone Building A - Headquarters 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 time- domain reflective technology to characterize and locate faults in metallic cables (for example, twisted-pair cable or coaxial cable)
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 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 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.
RF Phenomena Wireless Installations 2. 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 !)
RF Phenomena Wireless Installations 3. 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.
RF Phenomena Wireless Installations 4. 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. 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.
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.
