Types of Network:
Internet Protocol Address (IP Address) The Internet Protocol (IP) address identifies the network and host address assigned to a device.
Subnet Address The portion of the IP address that identifies the network the device is assigned to.
Local Area Network
(LAN) A group of computers and associated devices that share a common communications line or wireless link, typically to a server.
Metropolitan Area Network (MAN) All of the networks within the same metropolitan area that are connected together.
Wide Area Network
(WAN) A WAN connects several LANs. Wans are often limited to a corporation or an organization, but are sometimes accessible to the public.
Internet The internet is a collection of many different networks owned by many different entities that all share information and communicate together.
Intranet A local or restricted communications network, especially a private network created using World Wide Web software.
Extranet An intranet that can be partially accessed by authorized outside users, enabling businesses to exchange information over the internet securely.
This section helps you prepare for the following certification exam objectives:
A network is a group of computers that can share information through interconnections. A network is made up of the following components:
• Computers (often called nodes or hosts)
• Transmission media—a path for electrical signals between devices
• Network interfaces—devices that send and receive electrical signals
• Protocols—rules or standards that describe how hosts communicate and exchange data
Despite the costs of implementation and maintenance, networks actually save organizations money by allowing them to:
• Consolidate (centralize) data storage
• Share peripheral devices like printers
• Increase internal and external communications
• Increase productivity and collaboration
There are several ways to classify networks. The following table lists several ways to describe a network:
In a peer-to-peer network, each host can provide network resources to other hosts or access resources located on other hosts. Each host is in charge of controlling access to those resources. Advantages of peer-to-peer networks include the following:
• Easy implementation
Disadvantages of peer-to-peer networks include the following:
• Difficult to expand (not scalable)
• Difficult to support
• Lack centralized control
• No centralized storage
2. Wide Area Network (WAN)
A wide area network is a group of LANs that are geographically isolated, but are connected to form a large internetwork.
3.Controller Area Network (CAN)
A Controller Area Network (CAN) is designed to allow communication between microcontrollers and devices. CAN includes hardware specifications for the physical network and software specifications for communication. CAN was originally developed for the automotive industry to replace the complex wiring harness with a two-wire bus. CANs cost, performance, and easy upgrade process provide flexible system design.
CAN uses the following topologies:
The term network often describes a computer system controlled by a single organization. This could be a local area network at a single location or a wide area network used by a single business or organization. If two companies connected their internal networks to share data, you could call it one network. In reality, however, it is two networks because each network is managed by a different company.
A subnet is a portion of a network with a common network address.
•All devices on the subnet share the same network address, but they have unique host addresses.
•Each subnet in a larger network has a unique subnet address.
•Devices connected through hubs or switches are on the same subnet. Routers are used to connect multiple subnets.
In a client-server network, hosts have specific roles. For example, some hosts are assigned server roles, which allow them to provide network resources to other hosts. Other hosts are assigned client roles, which allow them to consume network resources. Advantages of client-server networks include the following:
•Easy to expand (scalable)
•Easy to support
•Easy to back up
Disadvantages of client-server networks include the following:
•Expensive server operating systems
•Extensive advanced planning required
1. Personal Area Network (PAN)
A personal area network is a very small network used for communicating between personal devices. For example, a PAN may include a notebook computer, a wireless headset, a wireless printer, and a smart phone. A PAN is limited in range to only a few feet. A PAN is typically created using Bluetooth wireless technologies.
2.Local Area Network (LAN)
A local area network is a network in a small geographic area, like an office. A LAN typically uses wires to connect systems together.
3.Wireless Local Area Network (WLAN)
A wireless LAN covers an area that is roughly the same size as a standard LAN. However, it uses radio signals instead of wires to connect systems together.
4.Metropolitan Area Network (MAN)
A metropolitan area network is a network that covers an area as small as a few city blocks to as large as an entire metropolitan city. MANs are typically owned and managed by a city as a public utility. Be aware that many IT professionals do not differentiate between a wide area network and a MAN as they use the same network technologies.
A network with geographically dispersed WAN connections that connect multiple LANs is often called an internetwork. Additionally, connecting two networks under different management is a form of internetworking because data must travel between two networks.
The internet is a large world-wide public network. The network is public because virtually anyone can connect to it, and users or organizations make services freely available on the internet.
•Users and organizations connect to the internet through an internet service provider (ISP).
•The internet uses a set of communication protocols (TCP/IP) for providing services.
•Individuals and organizations can make services (such as a website) available to other users on the internet
An intranet is a private network that uses internet technologies. Services on an intranet are only available to hosts that are connected to the private network. For example, your company might have a website that only employees can access.
An extranet is a private network that uses internet technologies, but its resources are made available to external (but trusted) users. For example, you might create a website on a private network that only users from a partner company can access.
Topology is the term used to describe how devices are connected and how messages flow from device to device. The physical topology describes the way the network is wired. The logical topology describes the way messages are sent.
LAN is the acronym for local area network. A LAN is a computer network that interconnects computers within a limited area.
Terminators absorb signals and prevent them from reflecting repeatedly back and forth on the cable. Terminators are used with bus topology.
Topology is the term used to describe how devices are connected and how messages flow from device to device.
There are two types of network topologies:
•The physical topology describes the way the network is wired.
•The logical topology describes the way messages are sent.
A bus topology consists of a trunk cable with nodes either inserted directly into the trunk or tapped into the trunk using offshoot cables called drop cables. When using a bus topology:
•Signals travel from one node to all other nodes.
•A device called a terminator is placed at both ends of the trunk cable.
•Terminators absorb signals and prevent them from reflecting repeatedly back and forth on the cable.
•It can be difficult to isolate cabling problems.
A broken cable anywhere on the bus breaks the termination and prevents communications between any devices on the network.
A ring topology connects neighboring nodes until they form a ring. Signals travel in one direction around the ring; each device on the network acts as a repeater to send the signal to the next device. With a ring:
•Installation requires careful planning to create a continuous ring.
•Isolating problems can require going to several physical locations along the ring.
•A malfunctioning node or cable break can prevent signals from reaching nodes further along on the ring.
A star topology uses a hub or switch to connect all network connections to a single physical location. Today it is the most popular type of topology for a LAN. With a star:
•All network connections are located in a single place, which makes it easy to troubleshoot and reconfigure.
•Nodes can be added to or removed from the network easily.
•Cabling problems usually affect only one node.
A mesh topology exists when there are multiple paths between any two nodes on a network. Mesh topologies are created using point-to-point connections. This increases the network's fault tolerance because alternate paths can be used when one path fails. Two variations of mesh topologies exist:
•Partial Mesh—Some redundant paths exist.
•Full Mesh—Every node has a point-to-point connection with every other node.
Full mesh topologies are usually impractical in a standard LAN because the number of connections increases dramatically with every new node added to the network. A separate network interface and cable for each host on the network is required. However, a full mesh topology is commonly used to interconnect routers, providing alternate paths should one path go down or become overloaded. Mesh networks are also commonly used to create redundant paths between access points in a wireless network, providing alternate paths back to the wireless controller should one access point go down or become overloaded. With this topology, every access point can communicate directly with any other access point on the wireless network.
The Open Systems Interconnection (OSI) model is a theoretical way of classifying and talking about the complex process of sending data on a network. You should be familiar with the OSI model because it is the most widely used method for understanding and talking about network communications. However, remember that it is only a theoretical model that defines standards for programmers and network administrators, not a model of actual physical layers.
OSI Model Benefits
The OSI model:
•Provides a common language and reference point for network professionals
•Divides networking tasks into logical layers for easier comprehension
•Allows specialization of features at different levels
•Aids in troubleshooting
•Promotes standards of interoperability between networks and devices
•Provides modularity in networking features (developers can change features without changing the entire approach)
OSI Model Limitations
However, you must remember the following limitations of the OSI model:
•OSI layers are theoretical and do not actually perform real functions.
•Industry implementations rarely have a layer-to-layer correspondence with the OSI layers.
•Different protocols are used within the OSI model to perform the different functions required to help send or receive the overall message. This can sometimes complicate the overall process.
•A particular protocol implementation may not represent every OSI layer (or may spread across multiple layers).
functions performed at each OSI model layer:
1. Application (Layer 7)
The Application layer integrates network functionality into the host operating system and enables communication between network clients and services. The Application layer does not include specific applications that provide services, but rather provides the capability for services to operate on the network.
Most Application layer protocols operate at multiple layers down to the Session and even Transport layers. However, these protocols are classified as Application layer protocols because they start at the Application layer (the Application layer is the highest layer where they operate). Services typically associated with the Application layer include:
2.Presentation (Layer 6)
The Presentation layer formats, or presents, data in a compatible form for receipt by the Application layer or the destination system. Specifically, the Presentation layer ensures:
•Formatting and translation of data between systems.
•Negotiation of data transfer syntax between systems by converting character sets to the correct format.
•Encapsulation of data into message envelopes by encryption and compression.
•Restoration of data by decryption and decompression.
3.Session (Layer 5)
The Session layer manages the sessions in which data are transferred. Session layer functions include:
•Management of multiple sessions (each client connection is called a session). A server can concurrently maintain thousands of sessions.
•Assignment of a session ID number to each session to keep data streams separate.
•The setup, maintenance, and teardown of communication sessions.
4.Transport (Layer 4)
The Transport layer provides a transition between the upper and lower layers of the OSI model, making the upper and lower layers transparent from each other. Transport layer functions include:
•End-to-end flow control.
•Port and socket numbers.
•Segmentation, sequencing, and combination.
•Connection services, either reliable (connection-oriented) or unreliable (connectionless) delivery of data.
At the Transport layer, data segments are called segments.
5. Network (Layer 3)
The Network layer describes how data is routed across networks and on to the destination. Network layer functions include:
•Identifying hosts and networks by using logical addresses.
•Maintaining a list of known networks and neighboring routers.
•Determining the next network point where data should be sent. Routers use a routing protocol that takes various factors into account, such as the number of hops in the path, link speed, and link reliability, to select the optimal path for data.
At the Network layer, data segments are called packets.
6.Data Link (Layer 2)
Logical Link Control (LLC)
Media Access Control (MAC)
The Data Link layer defines the rules and procedures for hosts as they access the Physical layer. These rules and procedures define:
•How physical network devices are identified on the network by defining a unique hardware address (physical or MAC address).
•How and when devices have access to the LAN and can transmit on the network medium (media access control and logical topology).
•How to verify that the data received from the Physical layer is error free (parity and CRC).
•How devices control the rate of data transmission between hosts (flow control).
At the Data Link layer, data segments are called frames. Switches, bridges and NICs, and WAPs function in Layer 2.
7.Physical (Layer 1)
The Physical layer of the OSI model sets standards for sending and receiving electrical signals between devices. Protocols at the Physical layer identify:
•How digital data (bits) are converted to electric pulses, radio waves, or pulses of light and moved across network cables.
•Specifications for cables and connectors.
•The physical topology.
At the Physical layer, data segments are called bits. NICs, repeaters, hubs, WAPs, and modems function in Layer 1.
TCP/IP Model Layers
The TCP/IP model incorporates the general concepts and structure of the OSI model. The layers of the TCP/IP model are as follows:
The Application layer corresponds to the Session, Presentation, and Application layers of the OSI model. Protocols associated with the Application layer include FTP, HTTP, Telnet, SMTP, DNS, and SNMP.
The Host-to-Host layer is comparable to the Transport layer of the OSI model. It is responsible for error checking and reliable packet delivery. Here, the data stream is broken into segments that must be assigned sequence numbers so they can be reassembled correctly on the remote side after they are transported. Protocols associated with the Host-to-Host layer include Transport Control Protocol (TCP) and User Datagram Protocol (UDP).
The Internet layer is comparable to the Network layer of the OSI model. It is responsible for moving packets through a network. This involves addressing hosts and making routing decisions to identify how the packet traverses the network. Protocols associated with the Internet layer include Address Resolution Protocol (ARP), Internet Control Message Protocol (ICMP), and the Internet Group Management Protocol (IGMP).
4. Network Access
The Network Access layer corresponds to the Physical and Data Link layers of the OSI model. It is responsible for describing the physical layout of the network and formatting messages on the transmission medium.
A protocol is a set of standards for communication between network hosts.
The internet protocol suite (frequently referred to as TCP/IP) is the most widely used protocol suite today.
•Protocols and ports
o SSH 22
o DNS 53
o SMTP 25
o SFTP 22
o FTP 20, 21
o TFTP 69
o TELNET 23
o DHCP 67, 68
o HTTP 80
o HTTPS 443
o SNMP 161
o RDP 3389
o NTP 123
o SIP 5060, 5061
o SMB 445
o POP 110
o IMAP 143
o LDAP 389
o LDAPS 636
o H.323 1720
A protocol is a set of standards for communication between network hosts. Protocols often provide services, such as email or file transfer. Most protocols are not intended to be used alone and rely on interaction with other dependent or complimentary protocols. A protocol suite is a group of protocols intended to be used together.
The internet protocol suite (frequently referred to as TCP/IP) is the most widely used protocol suite today.
1. Hypertext Transfer Protocol (HTTP)
Web browsers and web servers use HTTP to exchange files (such as web pages) through the world wide web and intranets. HTTP can be described as an information requesting and responding protocol. It is typically used to request and send web documents, but is also used as the protocol for communication between agents that employ different TCP/IP protocols.
2. HTTP over SSL (HTTPS)
HTTPS is a secure form of HTTP that uses SSL to encrypt data before it is transmitted.
1.Secure Sockets Layer (SSL)
SSL secures messages being transmitted on the internet. It uses RSA for authentication and encryption. Web browsers use SSL to ensure safe web transactions. URLs that begin with https:// trigger your web browser to use SSL.
2.Transport Layer Security (TLS)
TLS ensures that messages being transmitted on the internet are private and tamper proof. TLS is implemented through two protocols:
•TLS Record can provide connection security with encryption (for example, with DES).
•TLS Handshake provides mutual authentication and choice of encryption method.
TLS version 1.2 (TLS1.2) is an updated version that improves security flaws found in TLS 1.0 and 1.1.
1.File Transfer Protocol (FTP)
FTP provides a generic method for transferring files. It can protect access to files by requiring user names and passwords, and it allows file transfer between dissimilar computer systems. FTP can transfer both binary and text files, including HTML, to another host. FTP URLs are preceded by ftp:// followed by the DNS name of the FTP server. To log in to an FTP server, use ftp://username@servername.
The FTP protocol does not use encryption. All data, including user names, passwords, and files, are sent over the network as clear text.
2.Trivial File Transfer Protocol (TFTP)
TFTP is similar to FTP. It lets you transfer files between a host and an FTP server. However, it does not provide user authentication or error detection. TFTP is often used when files need to be transferred between systems quickly. Because it does not perform error detection, TFTP is faster than FTP, but is susceptible to transmission errors.
3. Secure File Transfer Protocol (SFTP)
SFTP uses Secure Shell (SSH) to secure data transfers. SSH ensures that SFTP transmissions use encrypted commands and data, which prevents clear text data transmissions.
4.Secure Copy (SCP)
SCP is used to securely transfer files between systems. Like SFTP, SCP relies on SSH to ensure that data and passwords are not transmitted over the network in clear text.
1.Simple Mail Transfer Protocol (SMTP)
SMTP is used to route electronic mail through the internetwork. SMTP is used:
•Between mail servers for sending and relaying mail.
•By all email clients to send mail.
•By some email client programs, such as Microsoft Outlook, to receive mail from an Exchange server.
2.Post Office Protocol 3 (POP3)
POP3 is used to retrieve email from a remote server and download it to a local client over a TCP/IP connection.
An email client that uses POP3 for receiving mail uses SMTP for sending mail.
3.Internet Message Access Protocol version 4 (IMAP4)
IMAP4 is an email retrieval protocol designed to enable users to access their email from various locations without the need to transfer messages or files back and forth between computers. Messages remain on the remote mail server and are not automatically downloaded to a client system.
An email client that uses IMAP4 for receiving mail uses SMTP for sending mail.
1.Dynamic Host Configuration Protocol (DHCP)
DHCP is used to automatically assign addresses and other configuration parameters to network hosts. Using a DHCP server, hosts receive configuration information at startup, reducing the amount of manual configuration required on each host.
2.Domain Name System (DNS)
DNS is a distributed system throughout the internetwork that provides address and name resolution. For example, the name www.mydomain.com would be mapped to a specific IP address.
3. Network Time Protocol (NTP)
NTP is used to communicate time synchronization information between systems on a network.
4.Lightweight Directory Access Protocol (LDAP)
LDAP is used to search, retrieve data from, and update a directory service. The LDAP protocol follows a client/server model. One or more LDAP servers contain the directory data. The LDAP client connects to an LDAP Server to make a directory service request. By default, LDAP traffic is transmitted unsecured.
5.Secure Lightweight Directory Access Protocol (LDAPS)
LDAPS is the lightweight directory access protocol over TLS/SSL. Using LDAPS makes LDAP traffic confidential and secure. LDAPS uses TCP port 636.
1. Simple Network Management Protocol (SNMP)
SNMP is designed for managing complex networks. SNMP lets network hosts exchange configuration and status information. This information can be gathered by management software and is used to monitor and manage the network.
2.Remote Terminal Emulation (Telnet)
Telnet allows a computer to remotely access the console of a computer system somewhere else in the network. At one time, Telnet was widely used for remote management tasks, but it is rarely used today. Because Telnet does not use encryption, it is recommended that you use a secure alternative to Telnet for remote management tasks, such as SSH.
3.Secure Shell (SSH)
SSH allows for secure interactive control of remote systems. SSH uses RSA public key cryptography for both connection and authentication. SSH uses the IDEA algorithm for encryption by default, but it can use Blowfish and DES. SSH is a secure and preferred alternative to Telnet.
1.Transmission Control Protocol (TCP)
TCP provides services that ensure accurate and timely delivery of network communications between two hosts. TCP provides the following services to ensure message delivery:
•Sequencing of data packets
•Acknowledgement of packets sent
•Retransmission of lost packets
2.User Datagram Protocol (UDP)
UDP is a host-to-host protocol like TCP, but it does not acknowledge each packet transmitted, nor does it allow for retransmission of lost packets. This reduces its overhead, allowing for faster communications and making UDP ideal for applications like streaming audio and video. However, this speed comes at the expense of possible errors or data loss.
1.Internet Control Message Protocol (ICMP)
ICMP works closely with IP to prevent errors and control information by allowing hosts to exchange packet status information. Two common management utilities, ping and traceroute, use ICMP messages to check network connectivity. ICMP also works with IP to send notices for the following:
•When destinations are unreachable
•Which route and hops a packet takes through the network
•Whether devices can communicate across the network
2.Internet Group Management Protocol (IGMP)
IGMP defines host groups. All group members can receive broadcast messages (multicasts) intended for the group. Multicast groups can be composed of devices within the same network or across networks (connected with a router).