Handson Networking Fundamentals

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Hands-on Networking Fundamentals

• Chapter 3
• Using Network Communication Protocols

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An Overview of Network Protocols

• Protocols enable effortless interchange of data
• Analogy protocols are like dialects of a
  language
• Computer communication requires common protocol
• Human communication requires common dialect
• LANs may transport multiple protocols
• Network device (such as router) makes
  distinctions
• Example An Ethernet may host TCP/IP for Windows
  server AppleTalk for Macintosh computer
• Pros and cons of hosting multiple protocols
• Pro allows networks to perform many different
  functions on a LAN
• Con the volume of network traffic increases

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Properties of a LAN Protocol

• Protocols have different strengths and drawbacks
• Example 1 some (not all) protocols are routable
• Example 2 some protocols have poor error
  checking
• Some protocols typically used on LANs
• IPX/SPX, NetBEUI, AppleTalk, and TCP/IP
• TCP is most widely used due to relation to
  Internet

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Understanding IPX/SPX

• Internetwork Packet Exchange (IPX)
• Developed by Novell for NetWare operating system
• NetWare used with Ethernet bus, token ring,
  ARCnet
• Modeled after Xerox Network System (XNS) protocol
• Sequenced Packet Exchange (SPX)
• Companion protocol to IPX
• Developed for use with applications, such as
  databases
• IPX/SPX used on NetWare servers through version 4
• TCP/IP is preferred protocol for NetWare 6 and
  above
• New NetWare versions can still implement IPX/SPX
• Advantage of IPX routable over multiple networks
  
• Disadvantage "chatty" protocol increasing
  traffic

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Understanding NetBEUI

• NetBEUI (NetBIOS Extended User Interface)
• Developed for LAN Manager and LAN Server
• Predates Windows NT
• NetBEUI used in early versions of Windows NT
• NetBEUI not supported in Windows XP or Windows
  Server 2003 (or higher)
• Disadvantages of NetBEUI
• Cannot be routed
• Causes unnecessary traffic

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Understanding Apple Talk

• AppleTalk protocol networks Macintosh computers
• AppleTalk is a peer-to-peer network protocol
• Enables Macs to communicate without server
• Windows Server 2003 and Novell use AppleTalk
• Enables communication with Mac computers
• AppleTalk Phase II
• Handles more networked computers than Phase I
• Interoperable with heterogeneous networks hosting
  multiple protocols

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Understanding AppleTalk

• Mac OS X Server built on Mac OSX operating system
• Both support either AppleTalk or TCP/IP
• Mac OS X Server support features
• File and printer sharing
• Managing network users and groups
• Providing Web services
• Typical deployments for Mac OS X Server
• Desktop publishing environments and school labs
• Windows and NetWare Servers can support Macs
• ApplTalk Phase II must be used by servers

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The History and Role of TCP/IP (recall)

• Advanced Research Projects Agency (ARPA)
• Networking goal enable university, research, and
  Defense Department to communicate
• ARPANET WAN prototype for modern networks
• An early protocol Network Control Protocol (NCP)
• Enabled DEC, IBM, and other hosts to communicate
• Did not provide wholly reliable communication
• TCP/IP combination of two protocols an
  improvement over NCP
• TCP (Transmission Control Protocol)
• IP (Internet Protocol)
• TCP/IP has become most widely used protocol suite
  

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The History and Role of TCP/IP (continued)

• Five advantages of TCP/IP
• Used worldwide on most networks and the Internet
• Influences design of wide range of network
  devices
• Main protocol of most computer operating systems
• Subject to many troubleshooting and network
  analysis tools
• Understood by large body of network professionals
• TCP/IP associated with a suite of protocols and
  applications

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Understanding TCP/IP

• TCP specified in RFC 793
• Designed for point-to-point communications
• IP specified in RFC 791
• Developed to link nodes in different networks or
  WANs
• TCP and IP first combined for use with UNIX
• TCP/IP layers may be roughly mapped to OSI layers
• Core components of TCP/IP protocol suite
• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)
• Internet Protocol (IP)

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How Transmission Control Protocol (TCP) Works

• TCP is a transport protocol (Layer 4 in OSI
  model)
• Establishes sessions between network nodes
• Sequences and acknowledges frames
• Provides for reliable end-to-end delivery
• Sequence number placed in TCP frame header
• Shows frame sequence in stream of frames
• Indicates amount of data in frames
• Sequence number checked for frame correctness
• Sliding window number of data bytes in frame
• May be dynamically adjusted if two nodes agree

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How Transmission Control Protocol Works
(continued)

• Main TCP functions (similar in OSI Transport
  layer)
• Monitor for session requests
• Establish sessions with other TCP nodes
• Transmit and receive data
• Close transmission sessions
• TCP ports used to form virtual circuit between
  nodes
• Enable multiple processes to communicate in
  session
• TCP segment header and data payload in TCP frame
• TCP header contains 11 fields
• Minimum length is 20 bytes

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How the User Datagram Protocol (UDP) Works

• User Datagram Protocol (UDP)
• Connectionless protocol
• Operates at OSI Layer 4 (like TCP)
• Alternative to TCP when high reliability not
  required
• Frame has four-field header and data
• Relies only on checksum to ensure reliability
• Connectionless protocol
• No flow control, sequencing, or acknowledgment
• Advantages adds little overhead onto IP
• Used with transaction processing applications
• Carries important network status messages

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How the Internet Protocol (IP) Works

• A LAN may be composed of series of subnetworks
• A WAN may comprise series of autonomous networks
• Examples DSL, SONET, X.25, and ISDN
• Communications enabled by Internet Protocol (IP)
• Between different subnetworks on a LAN
• Between different networks on a WAN
• Network transport options should be compatible
  with TCP/IP
• Transport options include Ethernet, token ring,
  X.25, FDDI, ISDN, DSL, frame relay, ATM

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How the Internet Protocol (IP) Works (continued)

• Basic IP Functions data transfer, packet
  addressing, packet routing, fragmentation,
  detection of errors
• Addressing essential for data transfer and
  routing
• 32-bit network node address used with 48-bit MAC
  address
• Connectionless protocol
• Provides network-to-network addressing and
  routing information
• Changes packet size when size varies with network
• Datagram TCP segment formatted with IP header
• IP packet header consists of thirteen fields

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How IP Addressing Works

• IP addressing used to identify two entities
• Specific node
• Network on which node resides
• Unique IP address enables accurate packet
  delivery
• Two nodes with same IP address create error
• IP addressing concepts fundamental in networking

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Basic IP Addressing

• Dotted decimal notation IP address format
• Four fields totaling 32 bits
• Fields are decimal values representing 8-bit
  binary octets
• Part of address is network ID, part is host ID
• Example in decimal format 129.5.10.100
• Five IP address classes, Class A through Class E
• Address reflects network size and transmission
  type
• Three types of transmission
• Unicast packet sent to each requesting client
• Multicast packet sent to group of requesting
  clients
• Broadcast communication sent to all network
  nodes

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The Role of the Subnet Mask

• TCP/IP requires configured subnet mask
• Subnet mask used for two purposes
• Show class of addressing used
• Divide networks into subnetworks to control
  traffic
• Example of a subnet mask
• 11111111.00000000.00000000.00000000 (255.0.0.0)
• Indicates Class A network
• Ones represent network/subnet identification bits
• Zeroes represent host identification bits

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Creating Subnetworks

• Subnet mask contains subnet ID
• Subnet ID contained within network and host IDs
• Subnet ID determined by network administrator
• Ex 11111111.11111111.11111111.00000000
  (255.255.255.0)
• Third octet in Class B address indicates subnet
  ID
• Subnet mask overrides four-octet length
  limitation
• Classless Interdomain Routing (CIDR) addressing
• Puts a slash ( / ) after the dotted decimal
  notation
• Number after slash represents bits in network ID
• Example (decimal) 165.100.18.44/18
• 18 bits needed for network ID, 14 for host ID (32
  -18)

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IP Address Rules

• Network number 127.0.0.0 cannot be assigned
• Address used for diagnostic purposes
• Certain IP network numbers reserved as private
• No one can use private addresses on Internet
• Designed for use behind NAT device e.g.,
  firewall
• May be used on private network with NAT device
• Network number cannot be assigned
• Highest number on a network cannot be assigned
• Address interpreted as broadcast message for
  subnet
• Example cannot assign 198.92.4.255

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The Promise of IPv6

• IPv6 developed through IETF initiative
• IPv6 overcomes limitations of IPv4
• Networks are beginning to transition to IPv6
• Five prominent features of IPv6
• 128-bit address capability
• Single address associated with multiple
  interfaces
• Address autoconfiguration and CIDR addressing
• 40-byte header instead of IPv4s 20-byte header
• New IP extension headers for special needs
• Includes more routing and security options

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The Promise of IPv6 (continued)

• Three IPv6 packet types unicast, anycast,
  multicast
• DES (Data Encryption Standard)
• Network symmetric-key encryption standard
• IPv6 supports DES compatible encryption
  techniques
• Benefits of IPv6 encryption capability
• Security over Internet
• Security over other types of LANs and WANs
• Disadvantage of IPv6 encryption capability
• Increases latency of network communications
• Latency travel time from sending node to
  receiving node

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TCP/IP Application Protocols

• Useful protocols and applications in TCP/IP suite
• Telnet
• Secure Shell (SSH)
• FileTransfer Protocol (FTP), Trivial FileTransfer
  Protocol (TFTP), and Network File System (NFS)
• Simple Mail Transfer Protocol (SMTP)
• Domain Name System (DNS)
• Dynamic Host Configuration Protocol (DHCP)
• Address Resolution Protocol (ARP)
• Simple Network Management Protocol (SNMP)
• Hypertext Transfer Protocol (HTTP), Secure
  Hypertext Transfer Protocol (S-HTTP), HTTP Secure
  (HTTPS)

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Telnet

• Telnet application protocol for terminal
  emulation
• Terminal device with a monitor and keyboard
• Examples IBM 3270 or DEC VT220
• Terminal emulation Computer behaving like
  terminal
• User access resources in a remote host
• Example Telnet with 3270 emulator connects to
  IBM mainframe like terminal
• Important Telnet features
• Comes with nearly all implementations of TCP/IP
• Open standard
• A number of communications options

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SSH

• Secure Shell (SSH)
• Provides authentication security for TCP/IP
  applications
• Used on many UNIX/Linux systems and in MAC OS X
• Circumstances for using SSH (if available)
• Remotely accessing a computer
• Uploading and downloading files
• How to start SSH application
• Enter ssh at the UNIX/Linux command line
• Learning about system dependent implementation
• Use the man ssh command in Linux and Mac OS X

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File Transfer Protocol (FTP), Trivial File
Transfer Protocol (TFTP), and Network File System
(NFS)

• FTP allows transfer of data between remote
  devices
• Transmissions may be binary or ASCII formatted
  files
• Transmissions ensured by connection-oriented
  service
• Limitation of FTP cannot transfer portion of
  file
• TFTP intended for transfer of small files
• Use for non-critical and non-secure transmissions
  
• Connectionless protocol running UDP instead of
  TCP
• NFS Sun Microsystem's alternative to FTP
• Uses connection-oriented protocol running in TCP

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Simple Mail Transfer Protocol (SMTP)

• Designed for exchange of electronic mail
• Two implementations
• For e-mail exchange between networked systems
• In local e-mail systems for Internet transport
• Provides alternative to FTP for file transfer
• Limited to sending text files
• Requires e-mail address on receiving end
• Does not require logon ID and password
• Two part message address header and message text
• Supported in TCP by connection-oriented service

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Domain Name System (DNS)

• Domain logical grouping of network resources
• Domains given unique names e.g., Microsoft.com
• DNS resolves domain names
• Resolution converts domain name to IP address
• Internet host domain names have two to three
  parts
• Top-level domain name (TLD) organization or
  country
• Optional subdomain name university/business name
• Host name name of computer
• Example myname_at_myorganization.com
• ICANN coordinates and registers root domain names

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Domain Name System (DNS) (continued)

• Namespace logical area with list of named
  objects
• Zones partitions in DNS server with resource
  records
• Forward lookup zone links computer name to IP
  address
• Reverse lookup zone links IP address to computer
  name
• Three servers related to DNS
• Primary DNS server authoritative server for zone
• Secondary DNS server backup servers
• Root servers find TLDs on the Internet
• Two DNS standards
• Service resource record (SRV RR)
• DNS dynamic update protocol

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Dynamic Host Configuration Protocol (DHCP)

• Enables automatic assignment of IP address
• Process of assigning address by DHCP server
• Newly configured computer contacts DHCP server
• DHCP server leases an IP address to new computer
  
• Lease length set on DHCP server by network admin
• Server or host may be given lease that does not
  expire
• IP address will never change with permanent lease

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Address Resolution Protocol (ARP)

• Enables sender to retrieve MAC address
• Process of obtaining MAC address
• Sending node sends ARP broadcast frame
• Frame has MAC address, IP address of recipient
• Receiving node sends back its MAC address
• Reverse Address Resolution Protocol (RARP)
• Used by network node to determine its IP address
• Used by applications to determine IP address of
  workstation or server

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Simple Network Management Protocol (SNMP)

• Enables steady monitoring of network activity
• Advantages
• Operates independently on the network
• Management functions carried out on special node
• Has low memory overhead
• Node types network management station (NMS) and
  network agents
• SNMPv2 offers better security, error handling,
  multiprotocol support, transmissions
• SNMP and SNMPv2 monitor LANs and WANS

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HTTP, S-HTTP, and HTTPS

• Hypertext Transfer Protocol (HTTP)
• Enables establishment of a Web connection
• Provides for exchange of resources
• Example displaying Web page in browser
• Secure Hypertext Transfer Protocol (S-HTTP)
• Used primarily in native HTTP communications
• Does not encrypt data in IP-level communications
• Hypertext Transfer Protocol Secure (HTTPS)
• Uses Secure Sockets Layer to implement security
• More common than S-HTTP

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TCP and the OSI Reference Model Compared

• Portions of TCP moving closer to OSI model
• Physical layer TCP supports coaxial,
  twisted-pair, fiber-optic, wireless communication
• Data Link layer TCP compatible with IEEE 802.2
  LLC and MAC addressing
• Network layer TCP/IP equivalent is IP
• Transport layer both TCP and UDP operate here
• Upper layers of OSI correspond to TCP/IP
  applications

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Transporting LAN Protocols Over WANs

• WAN protocols enable transport from LANs to WANs
• Serial Line Internet Protocol (SLIP)
• Encapsulates TCP/IP during connection session
• TCP/IP removed from SLIP after data payload
  received
• Compressed Serial Line Internet Protocol (CSLIP)
• Newly developed extension of SLIP
• Compresses header in each packet sent across link
  
• SLIP and CSLIP do not support
• Network connection authentication
• Setup of connections at multiple layers
• Synchronous connections

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Transporting LAN Protocols Over WANs (continued)

• Point-to-Point Protocol (PPP)
• Supports more network protocols than SLIP
• Automatically sets up connections with several
  layers
• Supports connection authentication and encryption
• Point-to-Point Tunneling Protocol (PPTP)
• Supplements PPP
• Enables remote communications via the Internet
• PPTP and PPP support synchronous communication
• PPTP and PPP support Password Authentication
  Protocol (PAP)