Home > Articles

This chapter is from the book

Internet Protocol Addressing Overview

IP version 4 (IPv4) addresses are made up of four 8-bit fields (octets)—32 bits total. There are five IPv4 address classes: A, B, C, D, and E.

IPv4 addresses consist of a network ID and a host ID. The network ID identifies the numeric network name of the physical network where the hosts exist. The host ID identifies the numeric network name of the individual TCP/IP host on a network. The numeric host ID must be unique on the internal network—that is, no two nodes on a network can have the same network ID and host ID.


You can have two hosts with the same numeric IP hostname of 16.72.28 if one is on network 111 and another is on network 112. (The full IP addresses of these hosts would be and The subnet mask would be

A subnet mask is used to divide an entire TCP/IP address in an effort to define which part of the address is the network number and which part is the host system's numeric identifier. The bits in a subnet mask are set consecutively from left to right. For example, the subnet mask is valid because all eight bits are set in the first two octets and the first bit of the next octet is also set (11111111.10000000.00000000.00000000). The subnet mask is not valid because it has a "missing" bit, which is not allowed (11111111.01000000.00000000.00000000).


Bit values are held to a specific order, from the Most Significant Bit (MSB) to the Least Significant Bit (LSB). From left to right, these designations are 128, 64, 32, 16, 8, 4, 2, and 1. Each bit that's set is noted by a "1" (showing that the bit is "on" or "enabled"), and bits are added together to give you the address. The IPv4 address converts to a binary number of 10101011.10010000.00111110.00001100 and a hexadecimal number of AB.90.3E.0C.


You need to have a fairly good understanding of host IDs, network IDs, subnetting, and masks for just about any Microsoft certification exam. Any exams that introduce information about networking require you to have at least basic knowledge of TCP/IP addressing.

IP version 6 (IPv6) has been designed to overcome the current shortage of addresses under IPv4 and offers some changes to TCP/IP. Table 3.1 outlines some of the major differences between IPv4 and IPv6.

Table 3.1 Differences Between IPv4 and IPv6




Address length in bits



Header size in bytes

20 to 60


IPSec support



Maximum Transmission Units (MTUs) in bytes



QoS support


Yes, with more features


Performed by hosts and routers

Performed by hosts only

Header checksum



Header options



Link-layer address resolution messages

Broadcast ARP frames

Multicast Neighbor Solicitation

Error reporting/diagnostic protocol

ICMP (for IPv4)


Multicast group membership protocol


Multicast Listener Discovery (MLD)

Support for router discovery



Network layer broadcast



Host configuration

DHCP or manual

Automatic, DHCP, or manual

DNS record type used for name resolution

(A) record

AAAA record

DNS record type used for reverse name resolution

PTR records in IN-ADDR.ARPA domain

PTR records in IP6.INT domain

The original IP definitions set five classes of IP addresses, from A through E. (A, B, and C are for general-purpose use, D is used for multicasting, and E is reserved.) These classes made it possible to use one portion of the 32-bit IP address scheme for the network address and the remaining portion for nodes on the network.

In the past, some networks needed more addresses for systems than the 254 supplied by a Class C address, which was a major contribution to the shortage of IP addresses. Organizations often requested a Class B range that offered 65,534 available addresses rather than a few Class C ranges that might have suited their needs. The result was that many addresses within their allotted Class B blocks went unused.

However, Classless Inter-Domain Routing (CIDR) addressing is now used more often for IPv4 addressing schemes. It effectively "removes" the class from an address for the purpose of combining ranges, so it makes better use of the limited number of remaining available IPv4 addresses. A CIDR network address looks like this: 

The network address is The /18 specifies that the first 18 bits of the address are the network part of the address, which leaves the last 14 bits for the network hosts' address.

CIDR is supported by Border Gateway Protocol (BGP) and OSPF. Older gateway protocols, such as Exterior Gateway Protocol (EGP) and Routing Information Protocol version 1 (RIPv1), do not support CIDR. Because CIDR supports multiple subnet masks per subnet, it requires routers that support more advanced interior routing protocols, such as RIPv2 and OSPF.


A, B, and C classful networks support a single subnet mask and can use RIPv1.

Subnet Masks

Implementing subnets helps control network traffic and enables network administrators to create smaller collision domains. Every node on the same physical ethernet network sees all data packets sent out on the network, which results in multiple collisions and affects network performance. Routers or gateways separate networks into subnets. Subnet masks on each node allow nodes on the same subnetwork to continue communicating with one another and with the routers or gateways they use to send their messages.

Subnet masks enables you to identify the network ID and host (node) ID of an IP address. The following example is a default Class B subnet mask:

IP Address       :
Address Class    : B
Network Address  :

Subnet Address   :
Subnet Mask      :
Subnet bit mask  : 10nnnnnn.nnnnnnnn.nnnnhhhh.hhhhhhhh
Subnet Bits      : 20
Host Bits        : 12
Possible Number of Subnets : 16
Hosts per Subnet : 4094

Selected Subnet  :
Usable Addresses : 4094
   Host range    : to
   Broadcast     :

To subnet networks further, more bits can be added to the subnet mask for a class of addresses.

The following example is a Class B address using an additional bit subnet mask of 240. Notice that instead of having the single subnet and 65,534 hosts per subnet allowed under the default subnet mask, you can have up to 16 subnets with up to 4,094 hosts per subnet by using a subnet mask of (Table 3.2 shows a sample IP addressing scheme):

11111111.11111111.11110000.00000000 Subnet Mask
IP Address       :
Address Class    : B
Network Address  :

Subnet Address   :
Subnet Mask      :
Subnet bit mask  : 10nnnnnn.nnnnnnnn.nnnnhhhh.hhhhhhhh
Subnet Bits      : 20
Host Bits        : 12
Possible Number of Subnets : 16
Hosts per Subnet : 4094

Selected Subnet  :
Usable Addresses : 4094
   Host range    : to
   Broadcast     :

Table 3.2 Example of an IP Addressing Scheme



Subnet Size

Host Range


4094 to

4094 to

4094 to

4094 to

4094 to

4094 to

4094 to

4094 to

4094 to

4094 to

4094 to

4094 to

4094 to

4094 to

4094 to

4094 to

When you use standard subnet masks in classful IP addressing schemes, you can plan how many hosts you can support per subnet and how many subnets are available for use. Table 3.3 shows classful IP addressing schemes and uses 255.x.0.0 as the default mask for Class A addresses, 255.255.x.0 as the default mask for Class B class addresses, and 255.255.255.x as the mask for Class C addresses. In these classes, the X is the subnet mask variable in the table's Subnet Mask column.

Table 3.3 Subnet Masking for Classful IP Addressing

Subnet Mask

Number of Subnets in Classful Range

Number of Class A Hosts per Subnet

Number of Class B Hosts per Subnet

Number of Class C Hosts per Subnet














































TCP/IP Class A Addresses

Class A addresses have an official start address of and an official ending address of However, the last usable client address in the range is, as the 127.x.x.x range is used for internal host loopback.

The full range of addresses that can be assigned to hosts is to, with as the broadcast address. The local host uses when it has been configured to use a DHCP server but cannot reach one and cannot assign itself an address using APIPA. (This situation would be unusual.)

There are 126 Class A networks total, and each is allowed to have up to 16,777,214 hosts. Three IP network addresses are reserved for private networks as defined in Request for Comment (RFC) 1918. The Class A range is to, with a subnet mask of

These addresses can be used by anyone setting up internal IP networks, such as a lab or home LAN behind a Network Address Translation (NAT) server, proxy server, or router. It is always safe to use them because routers on the Internet never forward packets coming from these addresses.

TCP/IP Class B Addresses

The Class B range of IP addresses starts with address and ends at address IP addresses to are the usable range of Class B addresses for node assignment.

Three IP network addresses are reserved for private networks, as defined in RFC 1918. The Class B range is to, with the subnet mask These addresses can be used by anyone setting up internal IP networks, such as a lab or home LAN behind a NAT server, proxy server, or router. It is always safe to use these addresses because routers on the Internet never forward packets coming from these addresses.

TCP/IP Class C Addresses

The Class C range of IP addresses starts at address and ends at IP addresses to are the usable range of Class C addresses for node assignment.

Three IP network addresses are reserved for private networks, as defined in RFC 1918. The Class C range is to, with the subnet mask These addresses can be used by anyone setting up internal IP networks, such as a lab or home LAN behind a NAT server, proxy server, or router. It is always safe to use them because routers on the Internet never forward packets coming from these addresses.

TCP/IP Class D Addresses

The Class D IP addresses range from through Internet Assigned Numbers Authority (IANA) has set aside this range as a special class of addresses for multicast uses. ISPs are unable to allocate Class D address space to their customers because IANA is the only body through which these addresses can be allocated.

Allocation of Class D addresses is required only if you want to be a multicast source. You can still receive multicast data without needing a separate Class D address.

TCP/IP Class E Addresses

IANA has set aside Class E IP addresses from to as a special class of addresses for experimental and future use. The IP address broadcasts to all hosts on the local network and, therefore, is not considered part of the Class E IP addresses.

Well-Known Ports

A number of well-known ports (0–1023) are used by different services on computers. For a single IP address on one system to offer all possible services to a network, each service must function on its own TCP or UDP port from that IP address.

You can find a helpful table at http://www.networksorcery.com that includes links to definitions and additional notes for some services. The following ports and associated protocols are the most important ones to remember:

  • 20—FTP—data

  • 21—FTP—control

  • 22—Secure Shell (SSH)

  • 23—Telnet

  • 25—SMTP

  • 37—Time Protocol (Time)

  • 49—Terminal Access Controller Access Control System (TACACS), TACACS+

  • 53—DNS

  • 67—BOOTP—server

  • 68—BOOTP—client

  • 69—TFTP

  • 70—Gopher

  • 79—Finger

  • 80—Hypertext Transfer Protocol (HTTP)

  • 88—Kerberos

  • 109—Post Office Protocol version 2 (POP2)

  • 110—Post Office Protocol version 3 (POP3)

  • 115—Simple File Transfer Protocol (SFTP)

  • 119—Network News Transfer Protocol (NNTP)

  • 123—Network Time Protocol (NTP)

  • 137—NetBIOS Name Service

  • 138—NetBIOS Datagram Service

  • 139—NetBIOS Session Service

  • 143—Internet Message Access Protocol (IMAP)

  • 153—Simple Gateway Monitoring Protocol (SGMP)

  • 161—SNMP

  • 162—SNMP—traps

  • 179—BGP

  • 389—Lightweight Directory Access Protocol (LDAP), Connectionless Lightweight X.500 Directory Access Protocol (CLDAP)

  • 443—HTTP over Secure Socket Layer/Transport Layer Security (SSL/TLS)—HTTPS

  • 464—Kerberos change/set password

  • 500—ISAKMP, Internet Key Exchange (IKE)

  • 546—DHCPv6 client

  • 547—DHCPv6 server

  • 631—Internet Printing Protocol (IPP)

Pearson IT Certification Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Pearson IT Certification and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Pearson IT Certification products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.pearsonitcertification.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020