A+ OS Guide
Protocols and Standards
Every device on the network must have a unique MAC address to ensure proper receiving and transmission of data. The MAC address is a device's actual physical address, which is usually designated by the manufacturer of the device
Medium Access Control sublayer Operations The purpose of the MAC sublayer is to determine when each frame should be passed on to the physical layer to be transmitted as a data signal over the network. The MAC sublayer governs which devices have permission to transmit data over the network and when. There are four basic methods for controlling access to the network, polling, contention, token passing, and switching.
2.2 Identify the seven layers of the OSI model and describe their functions.
The Open Systems Interconnection (OSI) Reference Model is a modular framework for developing standards that are based on a division of network operations into seven, sets of network services.
Data travels from the sending computer down through all the layers to the physical layer where the data is put onto the network cabling, and then sent to the physical layer of the receiving computer where the process reverses and the data travels up through the layers to the application layer of the receiving computer.
2.3 Differentiate between the following network protocols in terms of routing, addressing schemes, interoperability, and naming conventions:
Transmission Control Protocol, A connection based Internet protocol responsible for breaking data into packets, which the IP protocol sends over the network. IP is located at the TCP/IP Internet layer which corresponds to the network layer of the OSI Model. IP is responsible for routing packets by there IP address.
IP is a connectionless protocol. which means, IP does not establish a connection between source and destination before transmitting data, thus packet delivery is not guaranteed by IP. Instead, this must be provided by TCP. TCP is a connection based protocol and, is designed to guarantee delivery by monitoring the connection between source and destination before data is transmitted. TCP places packets in sequential order and requires acknowledgment from the receiving node that they arrived properly before any new data is sent.
Internetwork Packet Exchange/Sequenced Packet Exchange developed by Novell and is used primarily on networks that use the Novell NetWare network operating system. The IPX and SPX protocols provide services similar to those offered by IP and TCP. Like IP, IPX is a connectionless network layer protocol. SPX runs on top of IPX at the transport layer and, like TCP, provides connection oriented, guaranteed delivery.
IPX nodes do not have to be configured with a unique node identifier; instead, they copy the MAC address of the network interface card into the IPX node address field. The IPX header contains information about which transport layer protocol receives a particular packet. With IPX, this information is contained in the destination socket field. Servers have pre specified destination socket numbers, so workstations always know what value to use to send information to the server. In contrast, these workstations assign source socket numbers dynamically for their own protocols outside the server socket number's range.
IPX routing protocols require each logical network to have a different network number in order to forward IPX packets correctly. But, unlike IP, with IPX only servers and routers must be configured with a network number. New network stations first use dynamic Routing Information Protocol (RIP) routing packets to learn network topography and configuration from servers and routers and then configure themselves accordingly.
Because IPX is a connectionless protocol, NetWare servers are unable to tell if a station's connection to the server is currently active. To avoid reserving resources for inactive users, the NetWare server sends a watchdog packet to a client after a predetermined length of inactivity. The packet asks if the client is still connected and, if the client does not respond, the server terminates the connection.
SPX is connection oriented and, thus, does not require the use of watchdog packets. However, network devices will keep an SPX session open by sending keep alive packets to verify the connection.
NetBIOS Enhanced User Interface was designed as a small, efficient protocol for use in department-sized LANs of 20-200 computers that do not need to be routed to other subnets. NetBEUI is used almost exclusively on small, non-routed networks.
As an extension of NetBIOS, NetBEUI is not routable, therefore networks supporting NetBEUI must be connected with bridges, rather than routers, like NetBIOS, the NetBEUI interface must be adapted to routable protocols like TCP/IP for communication over WANs.
AppleTalk is a LAN architecture built into all Apple Macintosh computers. While AppleTalk is a proprietary network, many companies now market AppleTalk based products, including Novell and Microsoft. Similarly, designed to be link layer independent, AppleTalk supports Apple's LocalTalk cabling scheme, but also runs over Ethernet (EtherTalk), Token Ring (TokenTalk), and Fiber Distributed Data Interface, or FDDI (FDDITalk).
AppleTalk node addresses are assigned dynamically to ensure minimal network administration overhead. When a node running AppleTalk starts up, it generates a random network layer protocol address and then sends out a broadcast to determine whether that particular address is already in use. If it is, the node with the conflicting address responds and the broadcasting node selects a new address and repeats the inquiry process.
2.5 Identify the OSI layers at which the following network components operate:
hubs, switches, bridges, routers, and network interface cards
2.6 Define the purpose and function of the following protocols within TCP/IP:
Internet Protocol is the standard for data packet delivery over the Internet. IP is a network layer protocol that provides network addressing for identifying senders and receivers. IP also defines how data packets can be routed across the network to their destinations.
Routers forward each packet across the Internet based on its destination IP address. Each device attached to the Internet or any IP network must have a unique IP address.
Transmission Control Protocol, A connection-based Internet protocol responsible for breaking data into packets, which the IP protocol sends over the network. This protocol provides a reliable, sequenced communication stream for network communication.
User Datagram Protocol runs on top of IP and is used as an alternative to TCP. UDP does not, however, provide any error checking for guaranteeing packet delivery. Because UDP is not as complex as TCP, it is also faster. It is often used for broadcast messages and for streaming audio and video. UDP is a connectionless transport protocol.
File Transfer Protocol, is used for exchanging files in a TCP/IP environment and is implemented at the application layer of the OSI model.
TFTPTrivial File Transfer Protocol is a file transfer protocol that transfers files to and from a remote computer running the TFTP service. TFTP was designed with less functions than FTP.
Simple Mail Transfer Protocol, is used to transfer messages between two remote computers. It is used on the Internet, and is part of the TCP/IP protocol stack.
Hypertext Transfer Protocol is the underlying protocol for the World Wide Web. HTTP defines how all resources on the web are transferred and what action web servers and browsers should take in response to commands.
HTTP is a "stateless" protocol, meaning each command is executed independently, without any knowledge of the commands that came before it.
The secure hypertext transfer protocol is a communications protocol designed to transfer encrypted information between computers over the World Wide Web. HTTPS is HTTP using a Secure Socket Layer (SSL). A secure socket layer is an encryption protocol invoked on a Web server that uses HTTPS. Most implementations of the HTTPS protocol involve online purchasing or the exchange of private information. Accessing a secure server often requires some sort of registration, login, or purchase. The successful use of the HTTPS protocol requires a secure server to handle the request.
Post Office Protocol, used to retrieve e-mail from a mail server. Most e-mail applications use the POP protocol, although some use the newer IMAP (Internet Message Access Protocol).
This older POP2 requires SMTP to send messages. While POP3, can be used with or without SMTP.
Short for Telecommunication Network, a virtual terminal protocol allowing a user logged on to one TCP/IP host to access other hosts on the network.
Internet Control Message Protocol is a maintenance protocol in the TCP/IP suite, required in every TCP/IP implementation, that allows two nodes on an IP network to share IP status and error information. ICMP is used by the ping utility to determine the readability of a remote system.
Address Resolution Protocol, is a TCP/IP protocol used to convert an IP address into a physical address, such as an Ethernet address. A host wishing to obtain a physical address broadcasts an ARP request onto the TCP/IP network. The host on the network that has the IP address in the request then replies with its physical hardware address.
The Network Time Protocol is used to synchronize the time of a computer client or server to another server or reference time source, such as a radio or satellite receiver or modem. It provides accuracy's typically within a millisecond on LANs and up to a few tens of milliseconds on WANs.
2.7 Define the function of common TCP and UDP ports.
All upper layer applications that use TCP or UDP have a port number that identifies the application. This enables the port number to identify the type of service that one TCP system is requesting from another.
Some commonly used ports
2.8 Given a network implementation scenario, select the appropriate network service (e.g., DHCP/bootp, DNS, NAT/ICS, WINS, and SNMP).
Dynamic Host Configuration Protocol is a server service. When a DHCP server is configured on a network , clients that support DHCP can request TCP/IP configuration information from the server. This makes makes configuration of TCP/IP much easier on the client computer.
For example the following can be automatically obtained:
All these setting are automatically binded to the network card of the client computer. It is possible for DHCP to assign a different IP address to a client each time the machine logs on to the network.
A DHCP/BOOTP relay agent is hardware or software that passes DHCP/BOOTP packets from one subnet to another subnet. If the routers that connect the subnet are RFC 1542 compliant routers, the DHCP/BOOTP relay agent can provide IP addresses to clients in multiple subnets. If the router cannot function as a relay agent, each subnet that has DHCP clients requires its own DHCP Server.
Domain Name System, enables short alphabetical names to be assigned to IP addresses to describe where a computer is located. For example instead of trying to remember an IP address composed of numbers, such as 22.214.171.124 you could with DNS type HTTP://www.microsoft.com.
Network Address Translation is a process that lets an entire network connect to a PPP server and appear as a single IP address, thus helping to conceal IP addresses from external hackers and to alleviate address space shortage.
While DNS resolves host names to IP addresses, WINS resolves NetBIOS names to IP addresses. Windows Internet Name Service provides a dynamic database of IP address to NetBIOS name resolution mappings.
WINS, determines the IP address associated with a particular network computer. This is called name resolution. WINS supports network client and server computers running Windows.
WINS uses a distributed database that is automatically updated with the names of computers currently available and the IP address assigned to each one.
DNS is an alternative for name resolution suitable for network computers with fixed IP addresses.
Simple Network Management Protocol, is a TCP/IP protocol for monitoring networks and network components. SNMP uses small utility programs called agents to monitor behavior and traffic on the network, in order to gather statistical data.
These agents are can be loaded onto managed devices such as hubs, NIC's, servers, routers, and bridges. The gathered data is stored in a MIB (management information base).
To collect the information in a usable form, a management program console polls these agents and downloads the information from their MIB's, which then can be displayed as graphs, charts and sent to a database program to be analyzed.
IPv4 A, B, and C classes of IP addresses and their default subnet mask numbers
To accommodate different size networks, IP defines several address classes. Classes A, B, and C are used for host addressing, and the only difference between the classes is the length of the NET_ID subfield:
Class A - addresses are intended for very large networks and can address up to 16,777,216 (224) hosts per network. The first digit of a Class A addresses will be a number between 1 and 126, the network ID start bit is 0 and default subnet mask is 255.0.0.0
Class B - addresses are intended for moderate sized networks and can address up to 65,536 (216) hosts per network. The first digit of a Class B address will be a number between 128 and 191, the network ID start bit is 10 and the default subnet mask is 255. 255.0.0
Class C - intended for small networks and can address only up to 254 (28-2) hosts per network. The first digit of a Class C address will be a number between 192 and 223, the network ID start bit is 110 and their default subnet mask is 255. 255. 255.0
2.10 Identify the purposes of subnetting and default gateways.
A gateway is a device used to connect networks using different protocols. Gateways operate at the network layer of the OSI model.
In order to communicate with a host on another network, an IP host must be configured with a route to the destination network. If a configuration route is not found, the host uses the gateway to transmit the traffic to the destination host. The default gateway is where the IP sends packets that are destined for remote networks. If no default gateway is specified, communication is limited to the local network.
Gateways receive data from a network using one type of protocol stack, removes that protocol stack and repackages it with the protocol stack that the other network can use.
A subnet mask is used to mask a portion of the IP address, so that TCP/IP can tell the difference between the network ID and the host ID. TCP/IP uses the subnet mask to determine whether the destination is on a local or remote network.
2.12 Identify the basic characteristics (e.g., speed, capacity, media) of the following WAN technologies:
WAN technologies use either circuit switching or packet switching as a connection method.
With circuit switching, data travels over a fixed path that is established at the beginning of the connection and remains open until the connection is terminated. A telephone call is an example of a circuit switched link. When you dial a number the telecommunication provider, establishes an open circuit between your phone and the phone of the person you are calling. No other calls can be placed over this circuit until you hang up.
Packet switching offers more efficient use of a telecommunication provider's network bandwidth. With packet switching, the switching mechanisms on the network route each data packet from switch to switch individually over the network using the best-available path. Any one physical link in a packet-switched network can carry packets from many different senders and for many different destinations. Where as in a circuit switched connection, the bandwidth is dedicated to one sender and receiver only.
Integrated Services Digital Network adapters can be used to send voice, data, audio, or video over standard telephone cabling. ISDN adapters must be connected directly to a digital telephone network. ISDN adapters are not actually modems, since they neither modulate nor demodulate the digital ISDN signal.
Like standard modems, ISDN adapters are available both as internal devices that connect directly to a computer's expansion bus and as external devices that connect to one of a computer's serial or parallel ports. ISDN can provide data throughput rates from 56 Kbps to 1.544 Mbps using a T1 service.
ISDN hardware requires a NT (network termination) device, which converts network data signals into the signaling protocols used by ISDN. Some times, the NT interface is included, or integrated, with ISDN adapters and ISDN-compatible routers. In other cases, an NT device separate from the adapter or router must be implemented.
ISDN works at the physical, data link, network, and transport layers of the OSI Model.
Fiber Distributed Data Interface, shares many of the same features as token ring, such as a token passing, and the continuous network loop configuration. But FDDI has better fault tolerance because of its use of a dual, counter-rotating ring that enables the ring to reconfigure itself in case of a link failure. FDDI also has higher transfer speeds, 100 Mbps for FDDI, compared to 4 - 16 Mbps for Token Ring.
Unlike Token Ring, which uses a star topology, FDDI uses a physical ring. Each device in the ring attaches to the adjacent device using a two stranded fiber optic cable. Data travels in one direction on the outer strand and in the other direction on the inner strand. When all devices attached to the dual ring are functioning properly, data travels on only one ring. FDDI transmits data on the second ring only in the event of a link failure.
To transmit data Asynchronous Transfer Mode uses fixed sized packets of 53 bytes long called cells and provides data transfer rates from 25 Mbps to 2400 Mbps. ATM can be used with twisted pair and fiber optic cabling.
By using standard sized cells, ATM can provide constant, high-speed data streams that audio, video, and imaging applications require.
Frame Relay is a WAN technology, connection speeds range from 56 Kbps to 1.544 Mbps using a T1 carrier service, and speeds up to 45 Mbps using a T3 carrier service. Frame relay is a packet switched networking protocol.
To connect two or more LANs using Frame Relay, a company must lease one dedicated access line to the Frame Relay network for each LAN. Frame Relay access lines often use a T1/ E1 line.
Synchronous Optical Network, is a standard for optical telecommunications transport. It was formulated by the ECSA for ANSI, which sets industry standards in the United States for telecommunications and other industries. The comprehensive SONET/synchronous digital hierarchy (SDH) standard is expected to provide the transport infrastructure for worldwide telecommunications for at least the next two or three decades.
A 1.544 Mbps point to point dedicated, digital circuit provided by the telephone companies. T1 lines are widely used for private networks as well as interconnections between an organizations LAN and the telco.
A T1 line uses two pairs of wire one to transmit, and one to receive. and time division multiplexing (TDM) to interleave 24 64-Kbps voice or data channels. The standard T1 frame is 193 bits long, which holds 24 8-bit voice samples and one synchronization bit with 8,000 frames transmitted per second. T1 is not restricted to digital voice or to 64 Kbps data streams. Channels may be combined and the total 1.544 Mbps capacity can be broken up as required.
A T3 line is a super high-speed connection capable of transmitting data at a rate of 45 Mbps. A T3 line represents a bandwidth equal to about 672 regular voice-grade telephone lines, which is wide enough to transmit real time video, and very large databases over a busy network. A T3 line is typically installed as a major networking artery for large corporations, universities with high-volume network traffic and for the backbones of the major Internet service providers.
Optical Carrier, designations are used to specify the speed of fiber optic networks that conforms to the SONET standard.
2.13 Define the function of the following remote access protocols and services:
Remote Access Service A service that provides remote networking for telecommuters, mobile workers, and system administrators who monitor and manage servers at multiple branch offices. Users with RAS can dial in to remotely access their networks for services such as file and printer sharing, electronic mail, scheduling, and SQL database access.
Point to point Protocol facilitates Internet connections over serial lines, including modem connections. PPP software requires only a destination address usually a phone number for modem connections and a user login in order to negotiate a complete configuration for each session.
Virtual private network A remote LAN that can be accessed through the Internet by using PPTP
2.14 Identify the following security protocols and describe their purpose and function:
IP Security, is a set of protocols used to support secure exchange of packets at the IP layer.
IPsec supports two encryption modes: Transport and Tunnel. Transport mode encrypts only the data portion of each packet, but leaves the header untouched. The more secure Tunnel mode encrypts both the header and the data portion.
For IPsec to work, the sending and receiving devices must share a public key. This is accomplished through a protocol known as Internet Security Association and Key Management Protocol/Oakley, which allows the receiver to obtain a public key and authenticate the sender using digital certificates.
Layer Two Tunneling Protocol, an extension to the PPP protocol that enables ISPs to operate Virtual Private Networks. L2TP combines the best features of two other tunneling protocols: PPTP from Microsoft and L2F from Cisco Systems.
PPTP is a networking technology that supports multiprotocol virtual private networks, enabling remote users to access networks securely across the Internet by dialing into an ISP or by connecting directly to the Internet.
Secure Sockets Layer is a protocol that supplies secure data communication through data encryption and decryption. SSL enables communications privacy over networks by using a combination of public key, and bulk data encryption.
An authentication system, Kerberos is designed to enable two parties to exchange private information across an open network. It works by assigning a unique key, called a ticket, to each user that logs on to the network. The ticket is then embedded in messages to identify the sender of the message.
2.15 Define the purpose and function of Voice Over IP.
VoIP is the ability to make telephone calls and send faxes over IP based data networks with a suitable quality of service (QoS) and superior cost/benefit.
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