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rBenefits of a LAN There are numerous benefits for having a LAN. Each network benefit is important and even critical to an organization's success. These benefits include: / Resource sharing / Workgroup / synergy Management A Centralized A Decentralized / Data access and integration / Economic benefits 1 LAN Architecture " Software An end-user appplication may use a software protocol suite such as the TCP/IP or ISO/OSI " Hardware The physical network medium designed to carry informational signals, such as coaxial, twisted-pair cable, of fibre-optical material carrying multiband moduated laser light. 2 LAN Architecture " Topology A network constructed of the afore mention materials on one or more interconnecting plans. " Backbone (bus topology) This has been the typical LAN topology for Ethernet since its inception. This configuration has one large co-axial cable running thoughout the area. IBM Compatible IBM Compatible IBM Compatible IBM Compatible IBM Compatible 3 LAN Architecture " Star configuration This method uses a central location or hub from which a number of signal carrying cables goes out to each individual device on the branch of the LAN. A single hub can serve from 2 to 128 Lan devices (maybe more) on a single network domain. One other advantage to the star configuration is that the maximum distance between any two nodes is always only two segments long. IBM Compatible IBM Compatible Workstation Workstation IBM Compatible Workstation Workstation IBM Compatible IBM Compatible IBM Compatible 4 LAN Architecture " Ring configuration A true configuration has two ports on every node: one for input and one for output Workstation Workstation Workstation Token-ring Workstation Workstation Workstation Workstation Workstation 5 LAN Methodologies " Ethernet - IEEE 802.3 Ethernet is assumed to be the LAN method unless other -wise stated. More than 85% of all installed network connections were Ethernet by the end of 1996. This means there are over 150 million interconnected workstations, PC and servers using Ethernet today. " ATM (Asynchronous Transfer Mode) ATM eliminates inefficiencies by dynamically sharing network bandwidth among multiple logical connectio ATM has been defined at speeds of 45 Mbps, 100 Mb 6 155 and up to 622 Mbps. LAN Methodologies " ATM (Continued) The ATM LAN equipment includes ATM switches, routers, hubs, bridges, and workstations. " Token Ring - IEEE 802.5 The Token Ring network was originally developed by IBM. It is still IBM's primary local-area network (LA technology. Token-passing networks move a small command frame, called a token around the (circular r network. Possession of the token grants the possessor the right to transmit data. To transmit data, the toke the token is changed to a data frame and the information 7 is attached. LAN Methodologies " FDDI - (Fiber Distrubuted Data Interface) FDDI is frequently used as a backbone technology as well as a means to connect high-speed computers in a local area. ISO (International Organization for Standardization created an international standand for FDDI. FDDI specifies a 100-Mbps, token-passing, dual-ring LAN using a fiber-optic transmission medium. 8 LAN Methodologies " FDDI - (Continued) The dual-ring fiber-optic medium allows for true bi-directional simultaneous full duplex operation at 100Mbps on each fiber chan FDDI uses optical fiber as a transmission medium. Optical fiber offers several advantages over traditional copper wiring: A A A A A Security (fiber does not emit electrical signals that can be trapped) Reliablility (fiber is immune to electrical interface) Speed (optical fiber has much higher throughput potential than copper cable) No interference from the outside EMI (electromagnetic interference) source. Does not produce any EME interfere with and other communication medium (also a security advantage) 9 LAN Components " Topology - A description of the physical construct or layout of a network. " Backbone - The primary connectivity mechanism of an Ethernet network. All systems that have connectivity on the backbone can have connectivity to each other. " Segment - A continuous length of cable commonly joined with other segments. " Repeater - A device that amplifies and regenerates the data signal bit by bit in order to extend the distance of the transmission. A repeate does not read or interpet the data. 10 LAN Components " Bridge - A device that connects two or more networks segments of the same physical media type. A bridge examines the hardware address fields of a network packet and the filt based on addresses from one network segment to another and vice versa. " Router - A device that has two or more network interfaces. It examines the software proto -col (IP) address, selects an appropriate travel path and forwards the packet accordin between seperate networks. Routers usually forward packets belonging to a single protoco family. " Gateway - A device that interconnects two or more communications networks based on different protocol suites. The gateway performs any necessary protocol conversions. " Switch - A multiport device which minimally functions as a bridge, and provides for the logical dynamic connection and disconnection between any two cable segments witho operator intervention. The switch is a high-speed device because multiple data paths can be established and used simultaneously. " Concentrator - The central device through which all hosts in a twisted pair Ethernet installation are connected. " Hub - A central device through which various types of network packets can flow. 11 Networking Models The three networking models that provide a framework for network communication are: = ISO/OSI reference model = TCP/IP suite (TCP/IP model or TCP/IP) = SPX/IPX (Sequenced Packet Exchange/ Internetwork Packet Exchange). 12 Networking Models SPX/IPX This is a propriety protocol operating on Nevell Netware local area networks. SPX/IPX uses most Ethernet network interfaces such as IEEE 802 802.3 and Ethernet-II. SPX/IPX is not supported on the internet. If informa destination are systems connected top the internet, the model must be converted to TCP/IP prior to making the connection to the internet. For a through treatment of integration SPX/IPX into TCP/IP environment, refer to: " Network Personal Computers With Tcp/IP, Craig Hunt, O'Rielly, 1995 " Novell's Guide to Integrating UNIX and Netware Networks, Novell Press,1994 13 Networking Models The ISO/OSI reference model uses seven layers to describe its network communications framework. Brief description of each layer are as follows: Application layer Consists of user-accessed application programs and network sevices. Presentation layer Defines the way in which cooperating networks represent data. Session layer Manages the connections between cooperating applications. Transport layer Responsible for end-to-end messaging from one application program to another, also knows as end-to-end communication. Network layer Manages data addressing and delivery between networks. This layer fragments data into smaller pieces that the data link layer can handle. Data link layer Manages the delivery of data across the physical network. This layer provides error detection and packet framing. Physical layer Describes network hardware, including electric signal characteristics such as voltage and current. 14 Networking Models The TCP/IP Model The TCP/IP model describes its network communications frame -work usign five layers. Brief descriptions of each layer are as follows: Application Layer Consists of user-accessed application programs and network services. This layer is also responsible for defining the way in which cooperating networks represent data. A gateway functions at this layer. Transport Layer Manages the transfer of data using unacknowledged transport protocols. This layer also manages the connections between cooperating applications. Internet Layer Manages data addressing and delivery between networks, as well as fragmenting data for the network interface layer. A router functions at this layer. Network Layer Manages the delivery of data across the physical network. A bridge works at this level. Physical Layer Describes the network hardware, including electical signal characteristics such as 15 Ethernet Definition Ethernet is a packet-switching network that is based on a 10 Mbytes/sec broadcast technology with distri -buted access control. Ethernet is composed of three major elements: = Hardware I/O that transfers data to and from a packet switching network of computers = A packet switching network allows concurrent multiple communications among nodes on a network. = The Ethernet packet which is a unit of data sent across a network = This unit of data includes the destination address, the source address, and a form of parity checking all wrapped around a block of information. = The Ethernet access method protocol (CSMA/CD), which is used to control packet transmission and flow over the Ethernet hardware. 16 CSMA/CD Hosts send messages on an Ethernet LAN using a Network Interface Layer protocol and CSMA/CD. Multiple access H o st h a s m e ssa g e Carrier sense T r a f f ic o n n e tw o r k ? Y e s N o se n d m e ssa g e Collision detect a n y c o llis io n Y e s N o su cce ss w a it , b a c k o ff e x p ( ) 17 Switched Ethenet Switched Ethernet reduces the number of collisions on a network by utilizing an intelligent buffering system and control of the backbone. By removing the physical backbone network wire and replacing it with a central hub device that can receive, store, and transmit packets. 18 Fast Ethenet Fast Ethernet is capable of burst rates up to 100 Mbytes/sec over a single duplex connection and over 200 Mbytes/sec on a full-duplex dual-ported configuration. In a dual-ported full-duplex configuration, data is always traveling one direction on a single cable from point A to point B and coming back on a different cable from point B to point A. 19 Multimode Ethenet Because of packet-switching and the Ethernet being so versatile and adaptable, an Ethernet network can incude a variety of network speeds and interfaces. Mixing products from various vendors is also possible because of the standards laid out in the IEEE 802.3 specifications. For example: W o r k s t a t io n W o r k s t a t io n W o r k s t a t io n W o r k s t a t io n W o r k s t a t io n W o r k s t a t io n T o k e n - r in g W o r k s t a t io n W o r k s t a t io n W o r k s t a t io n W o r k s t a t io n 1 0 B a se T F ib e r W o r k s t a t io n 1 0 0 B a se T F ib e r W o r k s t a t io n 1 - G b y te s /s e c E th e r n e t H U B 22 -6 M r T A be F i F ib e r S e rve r W o r k s t a t io n W o r k s t a t io n W o r k s t a t io n 20 Ethenet Address An Ethernet address is a host's unique hardware address. It is 48 bits long and is displayed as 12 hexadecimal digits (6 groups of 2 digits), separated by colons (:). An example of a complete Ethernet address is 8:0:20:1e:56:7D. Unique Ethernet addresses are administered by Xerox. The first three octets are vendor-specific and are designated by Xerox. Sun systems always begin with the sequence 8:0:20. Sun assigns the last three octets to Sun products it manufactures. This method ensures that each node on an Ethernet has a unique Ethernet address. Sending Messages There are two types of ethernet addresses which can be used to communicate across the network: = Unicast address A host sends a message to another host on the Ethernet using a unicast address. Individual host Ethernet addresses are used for one-to-one, unicast transmissions. = Broadcast address A hsot sends a message to all hosts on the Ethernet using a broadcast address. The Ethernet broadcast address is all one (ff:ff:ff:ff:ff:ff in hex). When an Ethernet frame is received with a destination address of all ones, the Network Interface layer passes it to the next layer. 21 Ethenet Frame Analysis An Ethernet frame is a single unit of data transported through the LAN. A frame is a series of bits with a definite beginning and end. The Ethernet specification describes how bits are encoded on the cable and how hosts on the network detect the beginning and end of a transmission. The following diagram illustrates the relationship in this analogy: Octet location: 1-6 Preamble 64 bits 7-12 13-14 15-1514(the max) last 4 octet D addr 48 bits S addr 48 bits Type 16 bits Data (maximum 1500 bytes) CRC 32 bits Host in an Ethernet LAN use this information to receive and transmit data. Premble The 64-bit Ethernet preamble field, composed of ones and zeros, is used for synchronization. Synchronization helps the network interface determine where an Ethernet frame begins. Destination Address The destination address field is the Ethernet address of the destination host. 22 Ethenet Frame (Continued) Source Address The source address field is the Ethernet address of the sending host. Type The fourth field of the Ethernet frame describes the type of data encapsulated in the Ethernet frame (such as IP, ICMP, Address Resolution Protocol (ARP) or Reverse ARP (RARP)). Data The data field holds a minimum of 46 bytes and a maximum of 1500 bytes of information. The network hardware determines the maximum number of octets of data in a frame. This is called the MTU (maximum transfer unit). If the data to be transmitted is less than 46 bytes, the data is padded with zeros to reach to reach the 46-byte minimum. Cyclical Redundancy Check (CRC) The CRC field is used for error detection. The value is calculated based on frame contents, by the sending host. The receiving host uses the same algorithm to recalculate the CRC upon arrival, and then compares it with the frame CRC value. If the two values are 23 Ethenet Frame Encapsulation A p p lic a tio n D a ta T ra n s p o rt h e a d e r A p p lic a tio n D a ta Internet header A p p lic a tio n D a ta Ethernet Header A p p lic a tio n D a ta 24 Useful Troubleshooting Commands Snoop Location - /usr/sbin/snoop You can use snoop to capture network packets and display their contents. Packets can be displayed as soon as they are recieved, or saved to a file. 25 Useful Troubleshooting Commands Netstat Location - /usr/bin/netstat Use the netstat - i command to show the state of the Ethernet interfaces. # netstat - i Name - The name of the device (interface). " Mtu - The maximum transfer rate in bytes. " Net/Dest - The network number. This field references the file /etc/inet/networks. This file is discussed later. " Address - The IP address for that interface. " Ipkts/Ierrs - Shows the input packets and errors. " Opkts/Oerrs - Shows the output packets and erros. " Coll - The number of collisions on this interface. " Queue - The number of packets awaiting transmission. " To display the contents of the routing table for the local system, use the netstat - r. command 26 Useful Troubleshooting Commands Ifconfig Location - /usr/sbin/ifconfig The ifconfig command is used to display information about the configuration of the network interface specified. The following example shows the configuration of a 100BaseT interface, including its IP and Ethernet addresses. # ifconfig hme0 hme0: flags=863<UP,BROADCAST,NOTRAILERS, RUNNING,MULTICAST> mtu 1500 inet 128.235.35.124 netmask ffffff00 broadcast 128.235.35.255 ether 8:0:20:80:d0:a7 27