Chapter 4 Internet Addressing and Operation

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Chapter 4 Internet Addressing and Operation

• Part 1 Data Communications in the Information Age

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Topics Addressed in Chapter 4

• Internal Addressing
• Internet naming conventions
• Subnet masks
• Static vs. dynamic IP addresses
• IP routing

• Internet tools for network managers
• Web page design tools
• Server configurations
• TCP/IP and security

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Converting to Binary
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Internet Addresses

• IPv4 is currently the standard for IP addressing
• IPv4 addressing is described in RFC 760
• 32-bit addresses are specified
• IPv6 addresses are 128-bits in length
• IPv6 is used in Internet2 and will be more widely
  used in the future on the Internet
• IP addressing is primarily concerned with
  establishing a unique identity for networked
  computers
• By doing this, IP addressing enables packets to
  be routed between networks and delivered to the
  appropriate host or node on the destination
  network

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IP Addressing Basics

• IPv4 addresses are usually written as four
  separate numbers delineated by a period
• For example 101.209.33.17
• This way of representing an IP address is called
  the dotted-quad notation
• Each number in the four-number group is
  represented as an 8-bit octet in an IPv4 header
• For example 101.209.33.17 would be represented
  as
• 01100101 11010001 00100001 00010001

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More IP Addressing Basics

• In IPv4, each 32-bit IP address is subdivided
  into network and host/node portions
• This is illustrated in Figure 4-2
• The composition of the first four bits in the IP
  address specifies whether the network portion is
  1, 2, or 3 bytes in length
• These four bits determine whether the host/node
  has a Class A, B, C, D, E address (see Table 4-1)

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Figure 4-2
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IPv4 Address ClassesTable 4-1
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IPv4 ClassesTable 4-2
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Reserved IP Addresses

• The developers of the IPv4 addressing scheme
  reserved three blocks of addresses for networks
  that would not be connected to the Internet
• These are identified and defined in RFC 1918
• Reserved address ranges are illustrated in Table
  4-3

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Table 4-3
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Domain Names

• For most Internet users, dotted-quad
  representations for Internet hosts/nodes are
  cumbersome. As a result, most users rely on
  domain name conventions instead
• Domain names are included in URLs
• A domain name is a word-orientated representation
  of an Internet address
• ICANN is responsible for approving domain names,
  including abbreviations used in URLs

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Domain Name Conventions

• The address elements of a domain name are ordered
  from most to least specific
• For example, in frodo.mycompany.com.us
• frodo probably represents the name of an Internet
  host owned by the company mycompany
• The com identifies the mycompany entity as a
  company and us identifies the country in which
  the hosts network is located
• The hierarchical nature of domain names is
  illustrated in Figure 4-3

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The Hierarchical Nature of Domain NamesFigure 4-3
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Domain Names and URLs

• When a domain name is included in a URL, it must
  be resolved to an IP address
• This is done by the Internets Domain Name System
  (DNS)
• Domain names and their IP addresses are stored in
  databases on domain name servers
• When a domain name must be resolved, a message is
  sent to the closest domain name server to obtain
  the IP address. If that server does not know the
  IP address, it sends a request to other domain
  servers for the information
• Once the IP address for a domain name is known,
  the host/node inserts the IP address as the
  destination address for the packet so that it can
  be routed to appropriate recipient

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URL Protocols

• HTTP is not the only TCP/IP protocol that uses
  URLs
• Others are identified in Table 4-7
• Although these differ slightly in format (see
  Table 4-8), all use domain names and therefore
  rely on the Domain Name System in order to operate

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Table 4-7
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Table 4-8
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Subnet Addressing

• Because there is a limited number of available
  IPv4 addresses, IPv4 developers provided
  mechanisms for sharing a single network address
  among two or more subnets
• These mechanisms are described in RFC 950
• RFC 950 enables class A, B, and C networks to be
  split into smaller networks that use the same
  network assignment numbers

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Subnetting Advantages

• Subnetting has the following advantages
• It simplifies network administration each
  network segment can be maintained independently
  and efficiently
• Intranets can be restructured without affecting
  the overall networks interfaces with the
  Internet and other external networks
• Because intranet subnetting is not visible to
  external networks it can be used to enhance the
  overall security of the organizations networks

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Subnetting Basics

• Subnetting enables network managers to extend the
  network portion of IPv4 addresses by taking away
  a portion of the host/node portion of the IP
  address
• The portion that is taken away is used as a
  subnet identifier
• This is illustrated in Figure 4-4

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Figure 4-4
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Subnet Masks

• A subnet mask is a binary bit pattern that is
  stored in hosts, nodes, and routers
• It is matched up with an incoming packets
  destination IP address to determine whether to
  accept or reject the packet
• Every TCP/IP network host/node or router stores a
  subnet mask along with its IP address (see Figure
  4-6)
• The subnet mask specifies which bits in an IP
  address should be treated as an extended network
  address (network subnet) and which bits
  represent the host/node portion of the address
• Default subnet masks exists for class A, B, and C
  networks (see Table 4-9)
• Table 4-10 summarizes alternative class C subnet
  masks
• Figure 4-5 illustrates how a subnet mask is used
  to decompose an IPv4 address into its subnet and
  host/node addresses

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Figure 4-6
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Table 4-9
Table 4-10
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Figure 4-5
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Static vs. Dynamic IP Addresses

• Host/node addresses can be allocated in one of
  two ways
• Static assignments
• Dynamic assignments
• Static IP addresses are permanently assigned to
  hosts and node
• Servers and routers are typically assigned static
  IP addresses
• These can be assigned to hosts/nodes through
  manual configuration or by always assigning the
  same IP address to a particular host/node when it
  comes online
• Dynamic IP addresses are automatically assigned
  to client stations in a TCP/IP network when they
  come online
• DHCP servers assign dynamic IP addresses to
  clients

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Dynamic Host Configuration Protocol (DHCP)

• The most common approach for dynamically
  assigning IP addresses is DHCP (Dynamic Host
  Configuration Protocol)
• Each DHCP server has a range of IP addresses that
  can be assigned and maintains a list of currently
  assigned and currently unassigned IP addresses
• DHCP client software enables a network host/node
  to request an IP address from a DHCP server when
  it comes online
• This process is illustrated in Figure 4-9
• When the client goes offline, it notifies the
  DHCP server that it is releasing the IP address.
  Once released, the IP address is placed on the
  DHCP servers assignable address list

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Figure 4-9
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Internet Addressing in LANs

• Additional addressing processes take place when
  the host/node that needs to connect to the
  Internet is in a LAN
• In LANs, physical (MAC) addresses (the address of
  the computers network interface cards) are used
  for message delivery
• When a LAN host/node has both an IP address and a
  MAC address, an incoming IP packet can only be
  delivered to the computer after the IP address
  has been translated to a MAC address
• The protocol that performs this function is
  address resolution protocol (ARP)

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Address Resolution Protocol (ARP)

• ARP servers maintain tables that contain
  host/node IP addresses and corresponding MAC
  addresses (see Table 4-12)
• If the destination nodes IP address is in the
  ARP table, it extracts the corresponding MAC
  address and uses it to build the MAC header
  needed to send the message to the node
• ARP is found at the Internet layer of the TCP/IP
  protocol stack (see Figure 4-10) but is often
  described as overlapping the Internet and media
  access layers because of its role in translating
  IP to MAC addresses

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Table 4-12
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Figure 4-10
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IP Routing

• Routers leverage routing tables when determining
  how to route a packet to the destination nodes
  IP address
• Some of the information found in routing tables
  is found in Table 4-13
• Essentially, when a router receives a packet, it
  
• identifies the destination nodes IP address in
  the packet header
• consults the routing table to determine the best
  path to the destination nodes network across the
  Internet backbone
• Addresses the packet to the next router on the
  best path and transmits the packet out the
  appropriate port
• This process is illustrated in Figure 4-12

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Figure 4-12
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Ports and Sockets

• Once received by the destination host/node, a
  packet progresses up the layers of the TCP/IP
  protocol stack and is directed to the appropriate
  application
• Port numbers are included in TCP or UDP headers
  to identify the application layer protocol that
  generated the data in the packet
• Some port numbers are permanently assigned to
  applications/services (see Table 4-15)
• The combination of an IP address and a port
  number is called a socket
• For example, the socket notation for a Web page
  request on a Web server whose IP address is
  141.165.231.193 would be 141.165.231.19380

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Examples of Well-Known PortsTable 4-15
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Internet Tools for Network Managers

• Some of the Internet tools used by network
  managers include
• Finger (see Table 4-16)
• Ping (see Figure 4-13)
• Tracert (see Figure 4-14)
• WHOIS database

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Internet ToolsTable 4-16 Figure 4-13
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Figure 4-14
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Web Page Design Tools

• Some of the major Web page design tools include
• Hypertext Markup Language (HTML)
• Dynamic HTML (DHTML)
• Extensible Markup Language (XML)
• see Table 4-17 and Figure 4-16
• Vector Markup Language (VML)
• Precision Graphics Markup Language (PGML)
• Virtual Reality Markup Language (VRML)
• These all evolved from SGML (see Figure 4-15)
• GIF, JPEG, and PNG are examples of graphics files
  used by Web page designers (see Table 4-18)

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Server Configurations

• At large commercial Web sites, a group of servers
  may share a single URL. This collective host is
  called a server farm
• Server farms help ensure reliable access and
  fault tolerance
• Load balancing involves the use of a switch or
  router to transfer user requests to particular
  servers in a server farm (see Figure 4-17)
• In a server cluster, a group of servers acts as a
  single team and is responsible for allocating the
  total workload that they are responsible for
  handling

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Figure 4-17
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TCP/IP and Security

• Important TCP/IP security technologies include
• Proxy servers that stand between the Internet and
  a private network and help prevent outsiders from
  accessing internal addresses and other network
  details (see Figure 4-18)
• Network address translation (NAT) is an important
  proxy server capability
• Virtual private networks (VPNs) that use
  tunneling protocols, authentication, and
  encryption to establish private links for a
  corporate network across the Internet and other
  public networks
• IPSEC (Internet Protocol Security Architecture)
  that provides secure data transmission across IP
  networks via authentication and encryption (see
  Figure 4-19)

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Figure 4-18
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Figure 4-19
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IPSEC Uses

• Because IPSEC enables secure communications
  across public TCP/IP networks such as the
  Internet, it is used to
• Build secure VPNs among branch offices
• Implement secure remote access for teleworkers
• Create secure extranets with business partners
• Provide security for B2B e-commerce, e-mail, file
  transfers, remote logons, and other distributed
  applications

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Chapter 4 Internet Addressing and Operation

• Part 1 Data Communications in the Information Age