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Network Guide to Networks, Fourth Edition


Title: Linux+ Guide to Linux Certification Subject: Chapter One Created Date: 9/27/2002 11:29:22 PM Document presentation format: On-screen Show (4:3) – PowerPoint PPT presentation

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Title: Network Guide to Networks, Fourth Edition

Network Guide to Networks, Fourth Edition
  • Chapter 11
  • In-Depth TCP/IP Networking

Designing TCP/IP-Based Networks
  • Review of some TCP/IP fundamentals
  • IP is a routable protocol
  • On a network using TCP/IP, each interface
    associated with unique IP address
  • Some nodes may use multiple IP addresses
  • IP addresses consist of four 8-bit octets
  • Many networks assign IP addresses and host names
    dynamically, using DHCP
  • Every IP address can be associated with a network

  • Separates network into multiple, logically
    defined segments (subnets)
  • Each subnets traffic separated from every other
    subnets traffic
  • Enhances security
  • Subnetworks must be connected via routers or
    other Layer 3 devices
  • Improves performance
  • Data is selectively retransmitted
  • Simplifies troubleshooting

Classful Addressing
  • Adheres to network class distinctions
  • Only Class A, B, and C addresses are recognized
  • Network ID limited to first 8 bits in Class A,
    first 16 bits in Class B, and first 24 bits in
    Class C
  • Fixed network ID size ultimately limits number of
    hosts a network can include

Classful Addressing (continued)
Figure 11-1 Example IP addresses with classful
Subnet Masks
  • Subnetting depends on subnet masks to identify
    how a network is subdivided
  • Indicates where network information is located in
    an IP address
  • 1 bits indicate corresponding bits in IP
    address contain network information
  • 0 bits indicate corresponding bits in IP
    address contain host information
  • To calculate hosts network ID given IP address
    and subnet mask, perform ANDing

Subnet Masks (continued)
Table 11-1 Default subnet masks
Subnet Masks (continued)
Table 11-2 ANDing
Figure 11-2 Example of calculating a hosts
network ID
Reserved Addresses
  • Certain types of IP addresses reserved for
    special functions
  • In network IDs, bits for host information set to
  • In broadcast addresses, octet(s) representing
    host information set to all 1s (255 in decimal

Subnetting Techniques
  • Subnetting breaks rules of classful addressing
  • Some bits that in classful addressing would
    represent host information changed to represent
    network information
  • Reduce number of usable host addresses per subnet

Subnetting Techniques (continued)
Table 11-3 Class B subnet masks
Subnetting Techniques (continued)
Table 11-4 Class C subnet masks
Calculating Subnets
  • Formula for determining how to modify a default
    subnet mask 2n-2Y
  • n number of bits in subnet mask that must be
    switched from 0 to 1
  • Y number of subnets that result
  • Extended network prefix Additional bits used for
    subnet information plus existing network ID
  • Class A, B, and C networks can all be subnetted
  • External routers pay attention to only the
    network portion of devices IP addresses

Calculating Subnets (continued)
Figure 11-3 A router connecting several subnets
Calculating Subnets (continued)
Figure 11-3 (continued) A router connecting
several subnets
CIDR (Classless Interdomain Routing)
  • Classless routing or supernetting
  • Provides additional ways of arranging network and
    host information in an IP address
  • Supernet Subnet created by moving subnet
    boundary to the left
  • Generates more usable IP addresses
  • CIDR notation (slash notation) network ID
    followed by forward slash (/), followed by number
    of bits used for extended network prefix
  • CIDR Block

CIDR (continued)
Figure 11-4 Subnet mask and supernet mask
Figure 11-5 Calculating a hosts network ID on a
supernetted network
Internet Gateways
  • Combination of software and hardware enabling two
    different network segments to exchange data
  • Every device on a TCP/IP-based network has a
    default gateway
  • First interprets outbound requests to other
  • Interprets inbound requests from other subnets
  • Each node on network has one default gateway
  • May be network interface on a router
  • Must maintain routing tables as well
  • Core gateways make up the Internet backbone

Internet Gateways (continued)
Figure 11-6 The use of default gateways
NAT (Network Address Translation)
  • Default gateways can be used to hide IP numbers
    assigned within an organization
  • Clients behind gateway may use any IP addressing
  • Even non-legitimate schemes
  • Must have legitimate IP address to exchange data
    with Internet
  • NAT when clients transmission reaches default
    gateway, it assigns clients transmission a valid
    IP address

NAT (continued)
Figure 11-7 NAT through an Internet gateway
ICS (Internet Connection Sharing)
  • Computer with Internet access (ICS host)
    configured to translate requests to and from
    Internet on behalf of other computers on network
  • Acts as DHCP server, DNS resolver, and NAT
    gateway for clients on its LAN
  • Network adapter on ICS host assigned IP address
  • Clients must be set up to obtain IP addresses
  • ICS host assigns clients IP addresses in range of through

Intranets and Extranets
  • Intranet network or part of network that uses
    browser-based services to exchange information
    within an enterprise
  • Used for supplying HTTP-accessible documents,
    e-mail, file sharing, document management, and
  • Defined by its security policies
  • Extranet network that uses Internet-like
    services and protocols to exchange information
    within an organization and with certain,
    authorized users outside of that organization

TCP/IP Mail Services
  • E-mail is most frequently used Internet service
    that network administrators manage
  • Mail servers communicate with other mail servers
    to deliver messages across Internet
  • Hundreds of software packages for mail servers
  • Sendmail, Microsoft Exchange Server, Lotus Notes,
    Novell Groupwise
  • Mail clients send/retrieve messages to/from mail
  • Servers and clients communicate through TCP/IP
    Application layer protocols

SMTP (Simple Mail Transfer Protocol)
  • Protocol responsible for moving messages between
    mail servers over TCP/IP-based networks
  • Belongs to Application layer of TCP/IP Model
  • Relies on TCP at Transport layer
  • Operates from port 25
  • Relies on higher-level programs for instructions
  • Can only transport or hold mail
  • When configuring clients to use Internet e-mail,
    must identify users SMTP server

MIME (Multipurpose Internet Mail Extensions)
  • Standard SMTP message format allows for lines
    that contain 1000 ASCII characters max
  • Cannot handle pictures or formatted text
  • MIME standard for encoding and interpreting
    binary files, images, video, and non-ASCII
    character sets within e-mail messages
  • Identifies each element of a message according to
    content type
  • Works in conjunction with SMTP

POP (Post Office Protocol)
  • Application layer protocol used to retrieve
    messages from mail servers
  • POP3 is most current and commonly used version
  • Mail delivered and stored on mail server until
    user connects (via e-mail client) to retrieve
  • Mail deleted from server after retrieval
  • Minimizes use of server resources
  • Best suited to users who retrieve mail from same
    workstation all the time

IMAP (Internet Message Access Protocol)
  • Developed as sophisticated alternative to POP3
  • IMAP4 is most current version
  • Users can store messages on mail server
  • IMAP4 provides the following features
  • Retrieve all or only a portion of any mail
  • Review messages and delete them while the
    messages remain on the server
  • Create sophisticated methods of organizing
    messages on the server
  • Share mailboxes in a central location

Additional TCP/IP Utilities
  • TCP/IP comes with complete set of utilities that
    can help to track down most TCP/IP-related
  • e.g., Ping, Telnet, ARP
  • Nearly all TCP/IP utilities can be accessed from
    command prompt on any type of server or client
    running TCP/IP
  • Syntax may differ depending on OS
  • Options may differ according to OS

  • Displays TCP/IP statistics and details about
    TCP/IP components and connections on a host
  • Port on which a particular TCP/IP service is
  • Network connections currently established
  • Number of packets handled by network interface
    since activation
  • Number of data errors

Netstat (continued)
  • Common Netstat switches
  • -a lists all available TCP and UDP connections
  • -e displays details about all packets that have
    been sent
  • -n lists currently connected hosts according to
    their ports and IP addresses (in numerical form)
  • -p allows you to specify what type of protocol
    statistics to list
  • -r provides list of routing table information
  • -s provides statistics about each packet
    transmitted by a host, separated according to
    protocol type

  • Given NetBIOS name, get IP address
  • Common nbtstat switches
  • -a displays a machines name table given its
    NetBIOS name
  • -A displays a machines name table given its IP
  • -r lists statistics about names that have been
    resolved to IP addresses by broadcast and by WINS
  • -s displays a list of all the current NetBIOS
    sessions for a machine

  • Query DNS database from any network computer and
    find host name of a device by specifying its IP
    address, or vice versa
  • Provides hosts IP address, primary DNS server
    name, and address holding record for this name
  • Many options (switches)

  • Domain information groper (dig) similar to
  • Provides more detailed information than nslookup
  • e.g., specifics about resource records associated
    with host name
  • Many switches
  • Must be explicitly installed on Windows systems

Dig (continued)
Figure 11-11 Output of a simple dig command
  • Query DNS registration database and obtain
    information about a domain
  • Who is domain registered to?
  • Technical person responsible for domain?
  • Hosting entity?
  • DNS Server addresses?
  • Must install software to use on Windows systems
  • Web-based alternatives exist
  • e.g.,

Traceroute (Tracert)
  • Uses ICMP to trace path from one node to another
  • Identifies all intermediate hops
  • Useful for determining router or subnet
    connectivity problems
  • Transmits series of UDP datagrams to specified
  • Increases TTL as path is discovered
  • Traceroute may stop before completing
  • Device problem on path
  • Device does not accept ICMP transmissions
  • Often indicates firewall

  • TCP/IP administration utility for use with
    Windows NT, 2000, XP, and Server 2003 OSs
  • Provides information about network adapters IP
    address, subnet mask, and default gateway
  • Commonly used switches
  • /? displays list of available switches
  • /all displays complete TCP/IP configuration
    information for each network interface on device
  • /release releases DHCP-assigned addresses for all
    network interfaces
  • /renew renews DHCP-assigned addresses for all
    network interfaces

  • Same as ipconfig utility, but applies to Windows
    9x and Me OSs
  • Graphical interface

  • TCP/IP configuration and management utility used
    on UNIX-type of systems
  • Similar to ipconfig on Windows systems
  • Commonly used switches
  • -a applies command to all interfaces on a device
  • down marks interface as unavailable to network
  • up reinitializes interface after it has been
    taken down
  • Complete list of switches found in man pages

VoIP (Voice over IP)
  • Use of packet-switched networks and TCP/IP to
    transmit voice conversations
  • IP telephony
  • Objectives for implementing VoIP
  • Lower costs for voice calls
  • Supply new or enhanced features and applications
  • Centralize voice and data network management

VoIP (continued)
  • VoIP callers can use
  • Traditional telephone
  • IP telephones telephones designed for TCP/IP
  • Softphones computers equipped with microphone,
    speaker, and VoIP client software
  • IP telephones must have unique IP addresses
  • More difficult to transmit voice signals over a
    packet-switched network than data signals
  • Internet telephony VoIP carried via Internet
  • May also be carried over private lines

VoIP (continued)
Figure 11-16 Accessing a VoIP network from
traditional telephones
  • Subnetting separates one network or segment into
    multiple, logically defined segments, or subnets
  • Bits in a subnet mask that equal 1 indicate that
    corresponding bits in an IP address contain
    network information
  • Bits in a subnet mask that equal 0 indicate that
    corresponding bits in an IP address contain host
  • CIDR allows the creation of supernets, or subnets
    established by using bits that normally would be
    reserved for network class information

Summary (continued)
  • Gateways facilitate communication between
    different subnets
  • Every device on a TCP/IP-based network has a
    default gateway
  • NAT allows a network administrator to hide IP
    addresses assigned to nodes on a private network
  • ICS is a service that allows a network of
    computers to share a single Internet connection
    through an ICS host computer

Summary (continued)
  • SMTP is responsible for moving messages from one
    e-mail server to another over TCP/IP-based
  • POP is a mail retrieval protocol
  • IMAP4 allows users to store messages on the mail
    server, rather than always having to download
    them to the local machine
  • The netstat utility displays TCP/IP statistics
    and the state of current TCP/IP components and

Summary (continued)
  • The nslookup utility allows you to look up the
    DNS host name of a network node by specifying the
    nodes IP address, or vice versa
  • The traceroute utility useful for determining
    router or subnet connectivity problems
  • VoIP is the use of packet-switched TCP/IP-based
    networks to carry voice signals