Chapter 4
Internet Addressing and
Operation
Part 1: Data Communications in the Information Age
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
2
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
3
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
4
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)
5
Figure 4-2
6
IPv4 Address Classes
Table 4-1
7
IPv4 Classes
Table 4-2
8
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
9
Table 4-3
10
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
11
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 host’s
network is located

The hierarchical nature of domain names is
illustrated in Figure 4-3
12
The Hierarchical Nature of Domain Names
Figure 4-3
13
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 Internet’s 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
14
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

15
Table 4-7
16
Table 4-8
17
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
18
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 network’s 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 organization’s networks
19
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

20
Figure 4-4
21
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 packet’s 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
22
Figure 4-6
23
Table 4-9
Table 4-10
24
Figure 4-5
25
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
26
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 server’s assignable address list
27
Figure 4-9
28
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)
29
Address Resolution Protocol (ARP)



ARP servers maintain tables that contain host/node IP
addresses and corresponding MAC addresses (see Table 412)
If the destination node’s 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
30
Table 4-12
31
Figure 4-10
32
IP Routing



Routers leverage routing tables when determining how to
route a packet to the destination node’s 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 node’s IP address in the packet header
– consults the routing table to determine the best path to the
destination node’s 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
33
Figure 4-12
34
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
141.165.231.193:80
35
Examples of Well-Known Ports
Table 4-15
36
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
37
Internet Tools
Table 4-16 & Figure 4-13
38
Figure 4-14
39
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)
40
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
41
Figure 4-17
42
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)
43
Figure 4-18
44
Figure 4-19
45
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
46
Chapter 4
Internet Addressing and
Operation
Part 1: Data Communications in the Information Age