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Hands-on Networking
Fundamentals
Chapter 3
Using Network Communication Protocols
An Overview of Network Protocols
• Protocols enable effortless interchange
• Analogize protocols to dialects
– Computer communication requires common protocol
– Human communication requires common dialect
• LANs may transport multiple protocols
– Network device (such as router) makes distinctions
– Example: Ethernet hosts TCP/IP for Windows server,
AppleTalk for Macintosh computer
• Pros and cons of hosting multiple protocols
– Pro: networks perform many different functions on LAN
– Con: volume of network traffic increases
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Properties of a LAN Protocol
• Capabilities included in properties of LAN protocol
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Enable reliable network links
Communicate at relatively high speeds
Handle source and destination node addressing
Follow standards, particularly the IEEE 802 standards
• Protocols have different strengths and drawbacks
– Example 1: some (not all) protocols are routable
– Example 2: some protocols have poor error checking
• 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
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Activity 3-1: Configuring NWLink in
Windows XP
• Time Required: Approximately 5 minutes
• Objective: Configure a Windows XP client to
access NetWare using NWLink (similar for
Windows Server 2003).
• Description: Configure Windows XP to use Client
Service for NetWare and NWLink for accessing an
older NetWare server. Log on to Windows XP using
an account that has Administrator privileges.
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The History and Role of TCP/IP
• 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: 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
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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
• Associations enable TCP/IP to underlie vast range
of communications capabilities
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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
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)
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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:
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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)
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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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Activity 3-5: View the IP Address and
Subnet Mask Configuration in Windows
XP and Windows Server 2003
• Time Required: Approximately 5 minutes
• Objective: View and learn where to configure IP
addressing information in Windows XP and
Windows Server 2003
• Description: This activity enables you to view
where to set up the IP address and subnet mask in
Windows XP Professional or Windows Server
2003.
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The Promise of IPv6
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IPv6 developed through IETF initiative
IPv6 overcomes limitations of IPv4
Networks are beginning to transition to IPv6
Five prominent features of IPv6
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128-bit address capability
Single address associated with multiple interfaces
Address autoconfiguration and CIDR addressing
40-byte header instead of IPv4’s 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
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Top-level domain name (TLD): organization or country
Optional subdomain name: university/business name
Host name: name of computer
Example: [email protected]
• 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
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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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Activity 3-8: Configuring an SNMP
Agent
• Time Required : Approximately 15 minutes
• Objective: Learn to make Windows XP an SNMP
agent.
• Description: Windows XP can be configured to act
as an SNMP agent for a network management
station. In this project, you learn how to install
SNMP in Windows XP.
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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)
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Transporting LAN Protocols Over
WANs (continued)
• Layer Two Tunneling Protocol (L2TP)
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Similar to PPTP, and like PPTP used on VPNs
Like PPTP, L2TP encapsulates PPP
Creates special tunnels over public network (Internet)
Uses Layer Two Forwarding (based on MAC addresses)
• Signaling System 7 (SS7)
– For fast communications between different type WANS
– Supports call roaming, voicemail, redirection of 800 calls
– Adapted for T-carrier and other WAN communications
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Designing A Network To Use TCP/IP
And Application Protocols
• Scenario: network personnel in medical office
• Seven major components in network design
– Workstations and servers configured for TCP/IP
• Automatic (DHCP-based) IP addressing used
– DHCP used to lease IP addresses to workstations
• All servers given permanent IP addresses
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SNMP used in certain stations for network monitoring
Network browsers set up to use PPP for Internet links
Workstations set up to use FTP/HTTP through firewalls
E-mail system configured to employ SMTP
Primary DNS server and secondary DNS server set up
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