CDC

Transmission Control Protocol/Internet Protocol

) is the basic communication language or protocol of the Internet. TCP/IP is a suite of specialized protocols—including TCP, IP, User Data Protocol (UDP), ARP, and many others. TCP/IP would not have become so popular if it weren't routable. The TCP/IP suite offers a number of features and benefits, which are interoperability, flexibility and multivendor support.

Network number

identifies a specific network and must be assigned by Internet Assigned Numbers Authority (IANA) if the network is to be part of the Internet.

Class D address

are reserved for multicast addressing. The first four bits (1110) identify the address class and, together with the rest of the address, identify the network number.

Physical

A hub operates at this layer.

As few as two or three users or as many as thousands of users.

A local area network may serve how many users?

Network

A router operates at this layer.

Reserved addresses

A structured approach was taken to IPv6 reserved addresses. Any address that begins with "0000 0000" is reserved for various uses by the Internet Engineering Task Force (IETF). This represents 1/256 of the total address space of IPv6. Two special addresses used in IPv6 are as follows: 0:0:0:0:0:0:0:1 or ::1 is the loopback address. 0:0:0:0:0:0:0:0 or :: is the unspecified address (similar to the bootstrap address of a device that doesn't know its own address in IPv4).

Dual IP layer (also known as Dual Stack)

A technique for providing complete support for both Internet protocols: IPv4 and IPv6 (in hosts and routers).

Type of equipment the network needs; capabilities of the equipment; growth of the network; and way the network is managed.

A topology affects the network's capabilities; what is the impact of choosing one topology over another?

Multicast

identify a group of interfaces belonging to different nodes. Multicast packets are delivered to all interfaces identified by that address.

Transport

TCP operates at this layer.

Simple Mail Transfer Protocol

has the responsibility of transferring e-mail between computers. It uses the connection-oriented services of TCP to send and receive messages. APPLICATION LAYER

A telecommunications network

is a collection of network terminals, links and network nodes which are connected together enabling telecommunication or the transfer of data between terminal users.

Port 23-TELNET

TELNET is a user command and an underlying TCP/IP protocol for accessing remote computers TELNET, uses TCP port 23, and is one of the oldest protocols on the Internet. It allows remote logins to UNIX machines.

Application

Telnet, FTP, and SMTP that exist in the TCP/IP suite operate at this layer.

Presentation

At this layer, common data compression and encryption schemes are used.

Integrated Digital Network (IDN)

Digital phone network

Port 21-FTP

FTP is one of the oldest and most commonly exploited services on the Internet. The most common exploit of an FTP service is simply strangers using it to cache files. Never configure an FTP service such that somebody can both read and write to the same directory. Administrator should manually move "incoming" files to an "outgoing" directory.

Aggregatable Global

Finally, the last unicast address we will discuss is the Aggregatable Global Unicast Address. Aggregatable Global Unicast Addresses are essentially publicly accessible addresses. The Network ID portion of the address is broken up into different areas, allowing for hierarchical design and allocation.

Port 80-HyperText Transfer Protocol

For the HyperText Transfer Protocol (HTTP) service, port 80 is defined as a default and it does not have to be specified in the Uniform Resource Locator (URL).

Internet Protocol version 6 (IPv6)

IPv6 is expressed in 16-byte fields, which allows them to be more user friendly. Instead of using the Dotted Decimal Notation (DDN), IPng uses a colon hexadecimal format. that are 16 octets long, four times as large as IPv4

Port 138-NetBIOS datagram User Datagram Protocol

NetBIOS User Datagram Protocol (UDP) is a communications protocol that offers a limited amount of service when messages are exchanged between computers in a network that uses the Internet Protocol (IP) used by Windows. The main danger on the Internet is that by crafting special messages sent to this port, a hacker can convince Windows that their machine is "local", and can therefore bypass some of Microsoft's security settings that differentiate between "local" and "Internet" zones.

Classless subnet masking

If a further subdividing of the network (supernetting) is necessary beyond the class-full boundary, then bits can be borrowed from the host or node field to create the subnet field. This means that the octets beyond the class boundary can become values other than zero and are used to mask out the subnet field. Classless subnet masking is also known as Classless Inter-Domain Routing (CIDR, pronounced cider) was introduced in 1993 to allow more flexibility over the class-full address ranges of A-D. CIDR uses variable length subnet masks that will be discussed in greater detail in a later lesson. The Table 1-8 displays classless subnet values.

Application (upper) and data transport (lower) layers.

Into what two categories can you divide the OSI model?

Port 110-POP3

POP3 is the most recent version of a standard protocol for receiving E-mail. POP3 is a client/server protocol in which e-mail is received and held by a servicing Internet server.

reply ports

Ports 1024-65,536 are known as upper port numbers or reply ports

Port 161-Simple Network Management Protocol

Simple Network Management Protocol (SNMP) is the system used on the Internet to "manage" all the equipment that makes up the Internet. The equipment that composes the Internet consists of devices call "routers" that are interconnected via high speed phone lines. The most common use of SNMP is when an application sends queries at those routers requesting performance information on those lines. The goal is to detect which lines are congested (due to high traffic volume) to upgrade them to higher speed lines.

Data Link

Switches and bridges operate at this layer.

Internet

The Internet is a series of private computer networks (LANs and WANs) connected to each other often referred to as the World Wide Web or public Internet. Each individual private network is composed of a series of connected computers within an organization. Each organization takes responsibility for only the computers in its area of influence.

The Data Link layer, the Network layer (also known as the Internet layer in the TCP/IP model), the Transport layer, or the Application layer.

The easiest way to break down the many protocols of the TCP/IP suite is according to where they operate within the OSI model. Each protocol in this stack operates at what four layers?

Link-local

The first type of unicast address, the link-local address, operates within a network segment, and will not originate from, or be destined to, an interface that requires a router to direct traffic. In this case, link-local addresses operate similarly to layer-2 MAC addresses, allowing for quicker and more direct communication to interfaces on the same segment. Prefix length notation is FE80::/64.

Site-local

The next type of address is the Site-local address. They are designed to be private, internally routable addresses that do not route outside the site. Prefix length notation is FEC0::/48.

The standards that have been adopted by the IEEE as the Project 802 standards.

The protocols at the Data Link layer define the access method for the media, the architecture, and interface with the Physical layer of the network. What standards are these protocols based on?

Address range

The text representation of IPv6 address prefixes is similar to the way IPv4 addresses prefixes are written in CIDR notation. An IPv6 address prefix is represented by the notation: ipv6-address/prefix- length. The following is an example of IPv6 address range: FEDC:BA98:7654:3200::/56 - The number 56 signifies that from the leftmost part of the address and counting to the right 56 places belongs to the prefix. FEDC:BA98:7654:3200:: - This address is the start of the address range for host numbers using the prefix given above. FEDC:BA98:7654:32FF:FFFF:FFFF:FFFF:FFFF is the end of the address range for host numbers.

Port 8080-HTTP

This is a common port that contains HTTP servers and proxies. An imbedded management HTTP server that usually runs at this port through which any file on the system can be retrieved. Generally, you can put a proxy server on this port.

Port 443--Secure Socket Layer

This is the default port for HTTPS/Secure Socket Layer (SSL). This is the encrypted form of HTTP that normally runs over port 80. This is the default port used when you do credit card transactions with e-commerce sites.

Physical

This layer defines the electrical, mechanical, procedural, and functional specifications for network communications.

Session

This layer establishes, manages, and terminates communication sessions between presentation layer entities.

Presentation

This layer provides a variety of coding and conversion functions that are applied to application layer data.

Network

This layer provides routing and related functions that enable multiple data links to be combined into an Internetwork.

Transport

This layer typically includes multiplexing, virtual circuit management, and error checking and recovery.

Data Link

This layer's specifications include physical addressing, sequencing of frames, and flow control.

To reduce time spent on IP address management, to reduce the potential for errors in assigning IP addresses, and to make IP addressing transparent for mobile users.

What are some reasons for implementing DHCP?

Inexpensive to install; easy to add more workstations; requires less cable than other; works well for small networks (2-10 devices).

What are the advantages of a bus topology?

Data packets can travel at greater speeds; there are no collisions; and it is easier to locate problems with devices and cable; and no terminators are needed.

What are the advantages of a ring topology?

It's easy to add more devices as your network expands; the failure of one cable or one cable break will not bring down the entire network; the hub provides centralized management; it's easy to find device and cable problems; a star network can be upgraded to faster network transmission speeds; and it's the most common topology, so many equipment options are available.

What are the advantages of a star topology?

It's no longer a recommended option for new installations; if the backbone breaks, the network is down, only a limited number of devices can be included; it's difficult to isolate where a problem may be; and sharing the same cable means slower access time.

What are the disadvantages of a bus topology?

A star network requires more media than a ring or bus network; the failure of the central hub can bring down the entire network; and the costs of installation and equipment are higher than for most bus networks.

What are the disadvantages of a star topology?

A ring network requires more cable than a bus network; a break in the cable will bring many types of ring networks down when you add devices to the ring, all devices are suspended from us

What are the disadvantages of ring topology?

Source port, Destination port, Sequence number, Acknowledgment number (ACK), TCP header length, Reserved, Flags, Sliding-window size (or window), Checksum, Urgent pointer, Options, Padding, and Data.

What are the fields belonging to a TCP segment?

Internet Protocol (IP), Address Resolution Protocol (ARP), Reverse Address Resolution Protocol (RARP), and Internet Control Message Protocol (ICMP).

What are the four most important TCP/IP protocols that function within the network layer?

Star-bus and star-ring topologies.

What are the two most common hybrid topologies?

Local Area Network (LAN).

What is a group of computers and device that share a common communication line and resources in a small geographical area?

defines the way in which devices communicate and data is transmitted throughout the network.

What is a logical topology?

It is a "map," or description, of the layout of the network media that interconnects the devices on a network.

What is a physical topology?

Port 443-SSL is the default port used when you do credit card transactions with an e-commerce site.

What is the port used when you do credit card transactions with e-commerce sites?

Defining how data is sent across the physical media, through Internetwork devices, to the destination computer, and to the application on the destination machine.

What is the responsibility of the Data Transport layers of the OSI model?

If you can see it and touch it, it is physical. If you cannot see it or touch it, it is logical.

What is the rule of thumb to distinguish physical from logical topologies?

Virtual Private Network (VPN).

What network provides a private tunnel through the Internet?

Reply port.

What type computer port specifies a service that is a process or application that runs on a server and provides some benefit to a network user?

A Metropolitan Area Network or campus network.

What type of network is also used as a means to interconnect several local area networks by bridging them with backbone lines?

Port 109-Post Office Protocol 2

While Post Office Protocol 2 (POP2) has largely been replaced by Post Office Protocol 3 (POP3), hackers still scan for this port because many older POP3 servers have access holes in them.

Anycast

addresses are also used to identify a set of interfaces, but the packets are sent and accepted by the interface that is closest.

Unicast

addresses identify a single interface. A packet sent to a unicast address is delivered to the interface identified by that address.

Internet Protocol version 4 (IPv4)

addressing method is used throughout the entire Internet community. Its popularity is due to the wide acceptance and use of TCP/IP protocol suite. This addressing is used at layer 3 of the OSI model. An IP address identifies both the individual node and the network to which the node is attached. IPv4 addresses are represented as four sets of 8 binary bits; four OCTETS or BYTES, for a total of 32 bits. The IP address is often represented by a decimal conversion of each byte separated by a period (.). Each IP address has specific components and follows the same format. Each TCP/IP network is assigned a 32-bit logical address that is divided into two main parts: the network number and the host number

Zero compression

allows consecutive fields of zeros to be suppressed. This method is allowed once per address: Before suppression - 1080:0:0:0:8:0:0:417A. After suppression - 1080::8:0:0:417A (48-bits suppressed) or 1080:0:0:0:8::417A (32-bits suppressed). Suppression not allowed - 1080::8::417A.

Extranet

are Intranets that share a portion of their content with customers, suppliers, or other businesses, but not with the general public. As with Intranets, the same Web browsers and other software are used to access their content.

Intranet

are comprised of one or more LANs that are inter-connected within the company. But, unlike the Internet, the content is restricted to authorized company users only. Essentially, an Intranet is a private Internet.

well-known ports

are defacto standards used to ensure that everyone could access services on other machines without needing to guess which port number is used by the service.

Class E address

are reserved for research and development. The first four bits (1111) identify the address class and, together with the rest of the address, identify the network number. The first few bits in the string of binary digits that comprise the address identify the class of an IP address. For the course we will only be looking at classes A, B, and C.

Class A address

are used for large networks. The first bit (0) identifies the address class and, together with the next seven bits, identifies the network number. The last 24 bits are used to identify the node number. There are 126 class A networks (addresses 1-126), with 16,777,214 hosts on each network.

Class C address

are used for networks with about 250 nodes. The first three bits (110) identify the address class and, together with the next twenty-one bits, identify the network number. The last eight bits identify the node number. There are about 2,097,152 class C networks (addresses 192-223), with 254 hosts on each network.

Hybrid

combines two or more different physical topologies in a single network. The two most common hybrids found today are the star-bus and star-ring topologies.

Transport Layer Protocols

have the job of providing end-to-end communication between devices. The key function of the protocols at this layer is reliable and efficient delivery of data packets to the destination. In TCP/IP, there are two Transport layer protocols that provide the end-to-end communication services: Transmission Control Protocol (TCP). User Datagram Protocol (UDP). One of the most important distinctions between them is that TCP uses connection-oriented services, whereas UDP uses connectionless delivery.

Host number

identifies a specific host (or any node) on a network and is assigned by the local network administrator.

Leading Zero Compression

drops leading zeros in an address, in any field, as long as there is at least one number left: Original IPv6 format - 1234:1234:0000:0000:1234:0000:0000:1234. Using leading zero compression - 1234:1234:0:0:1234:0:0:1234.

Star-wired bus

groups of workstations are star-connected to hubs and then networked via a single bus. With this design, you can cover longer distances and easily interconnect or isolate different network segments. One drawback is that this option is more expensive than using either the star or, especially, the bus topology alone because it requires more cabling and potentially more connectivity devices. The star- wired bus topology forms the basis for modern Ethernet and Fast Ethernet networks.

Asynchronous Transfer Mode (ATM)

has grown out of the need for a worldwide standard to allow interoperability of information, regardless of the "end-system" or type of information.

Local Area Network (LAN)

is a group of computers and associated devices that share a common communications line and typically share the resources of a single processor or server within a small geographic area (for example, within an office building). Usually the server has applications and data storage that are shared by multiple computer users. A local area network may serve as few as two or three users or as many as thousands of users.

A subnet masking

is a mechanism that allows a network device to divide an IP address into a network and host number.

Metropolitan Area Network (MAN)

is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large LAN but smaller than the area covered by a WAN. The term is applied to the interconnection of networks in a city into a single larger network. It is also used to indicate the interconnection of several local area networks by bridging them with backbone lines. The latter usage is also sometimes referred to as a campus network.

Wide Area Network (WAN)

is a network that links LANs and MANs by using long-distance communication links that are leased or purchased from a telecommunications company. Long-distance communication links can be described as telephone lines, microwave, or satellite communications. A WAN connects networks that are typically separated by geographical distances. These distances are between two cities within a state, between two states, across a country, or around the world.

Network Time Protocol

is a simple protocol used to synchronize the clocks of computers on a network. APPLICATION LAYER

Internet Control Message Protocol

is a valuable protocol for network infrastructure technicians. It is implemented in all TCP/IP networks, and provides messaging that can help with troubleshooting. ICMP messages are included in the IP datagram. NETWORK LAYER

Dynamic Host Configuration Protocol

is an automated means of assigning a unique IP address to every device on a network. APPLICATION LAYER

Integrated Services Digital Network (ISDN)

is designed for a digital telecommunications network. This network promises to carry voice, data, and video on a single network via a single interface (in terms of both hardware and communication protocols) for connecting devices such as; telephones, faxes, computers, and video teleconferencing (VTC) equipment. ISDN provides the speed, accuracy, and flexibility of digital services over existing communications infrastructure; making it possible to combine both voice and data signals over standard phone lines originally designed for analog services. The slow evolution of ISDN has made it unpopular in the civilian sector and is widely considered out- dated technology. It is however, the DOD standard protocol for connecting secure telephone units (STE)'s, telephone switch trunks, and VTC.

User Datagram Protocol (UDP)

is responsible for end-to-end transmission of data. Unlike TCP, however, it does not establish a connection.

HyperText Transfer Protocol

is used to access Hypertext Markup Language (HTML) files on the Internet. It allows for clients and servers to exchange data very rapidly. HTTP offers only two types of messages to be exchanged: requests from the client and responses from the server. APPLICATION LAYER

Dotted Decimal Notation

is used to represent a binary IP address in a more user-friendly manner. The notation uses the combination value of each bit that is turned on (represented by a 1), in each byte or octet and adds them together. This is done for each octet individually; octet values are never added together.

File Transfer Protocol

is used to send and receive files via TCP/IP. APPLICATION LAYER

Simple Network Management Protocol

offers the ability to configure, monitor, and manage network resources and devices. APPLICATION LAYER

Virtual Private Network (VPN)

provides a private tunnel through a public cloud (the Internet). A VPN enables a group of two or more computer systems to communicate over the public Internet. VPN's may exist between an individual machine and a private network, or a remote LAN and a private, enterprise network. Secure VPN's make use of tunneling and security protocols to maintain the privacy of data transactions over the Internet. A VPN is a "virtual" as opposed to a "real" private network. The idea is to make a private network that provides a secure tunnel for the private exchange of data between two or more parties. If this were done over a "real" private network, the dedicated lines and service required would be cost prohibitive. But when the secure tunnel is implemented over a public network such as the Internet, there is no added cost to the service already in place. The two main drivers for using a VPN are remote access and extranet connections. Remote access is a requirement for our networks. Users that are in a temporary duty location may have a need to access their home network. A VPN allows for a secure, encrypted connection for the remote users, and can work over high-speed connections as well as dial-up connections, allowing for flexibility in operations. A VPN can also work as an extranet connection. This allows outside users access to data on the network through a secure web browser connection. The users will still need to authenticate themselves before they can gain access. A VPN can be set up as a peer-to-peer (P2P) or gateway-to-gateway connection. Most VPN traffic in the Air Force is done in the gateway-to-gateway configuration, securing the connection between the base and the rest of the Air Force enterprise network.

Internet Protocol (IP)

provides information about how and where data should be delivered, including the data's source and destination addresses. IP is the protocol that enables TCP/IP to Internetwork—that is, to pass through more than one LAN segment and more than one type of network through a router. NETWORK LAYER

Reverse Address Resolution Protocol

provides the reverse service to that of ARP. Rather than finding out the MAC address of a device whose IP address is already known, RARP provides the IP address for a device that knows its own MAC address. NETWORK LAYER

Address Resolution Protocol

provides the service of matching a known IP address for a destination device to a MAC address. NETWORK LAYER

protocol

the special set of rules used to communicate with each other.

Class B address

used for intermediate sized networks. The first two bits (10) identify the address class and together with the next fourteen bits, identify the network number. The last sixteen bits identify the node number. There are about 16,384 class B networks (addresses 128-191), with 65,534 hosts on each network.

Classful subnet masking

uses the default mask to separate the network number, given by Internet Assigned Numbers Authority (IANA), from the host number.

Star-wired ring

uses the physical layout of a star in conjunction with the ring topology's data transmission method. Data is sent around the star in a circular pattern. This hybrid topology benefits from the fault tolerance of the star topology (data transmission does not depend on each workstation to act as a repeater) and the reliability of token passing. Token Ring networks, as specified in IEEE 802.5, use this hybrid topology.

Network protocols

widely accepted communication standardized rules which govern how information will flow in communication networks.