Network
Content
Client- server network
The term client-server refers to a popular model for computer networking that utilizes client and server devices each designed for specific purposes. The client-server model can be used on the Internet as well as local area networks (LANs). Examples of client-server systems on the Internet include Web browsers and Web servers, FTP clients and servers, and the DNS. Client and Server Devices Client/server networking grew in popularity many years ago as personal computers (PCs) became the common alternative to older mainframe computers. Client devices are typically PCs with network software applications installed that request and receive information over the network. Mobile devices as well as desktop computers can both function as clients. Client-Server Applications The client-server model distinguishes between applications as well as devices. Network clients make requests to a server by sending messages, and servers respond to their clients by acting on each request and returning results. One server generally supports numerous clients, and multiple servers can be networked together in a pool to handle the increased processing load as the number of clients grows. A client computer and a server computer are usually two separate devices, each customized for their designed purpose. For example, a Web client works best with a large screen display, while a Web server does not need any display at all and can be located anywhere in the world. However, in some cases a given device can function both as a client and a server for the same application. Likewise, a device that is a server for one application can simultaneously act as a client to other servers, for different applications. [Some of the most popular applications on the Internet follow the client-server model including email, FTP and Web services. Each of these clients features a user interface (either graphic- or text-based) and a client application that allows the user to connect to servers. In the case of email and FTP, users enter a computer name (or sometimes an IP address) into the interface to set up connections to the server. Local Client-Server Networks Many home networks utilize client-server systems without even realizing it. Broadband routers, for example, contain DHCP servers that provide IP addresses to the home computers (DHCP clients). Other types of network servers found in home include print servers and backup servers. Client-Server vs Peer-to-Peer and Other Models The client-server model was originally developed to allow more users to share access to database applications. Compared to the mainframe approach, client-server offers improved scalability because connections can be made as needed rather than being fixed. The client-server model also supports modular applications that can make the job of creating software easier. In so-called "two-tier" and "three-tier" types of client-server systems, software applications are separated into modular pieces, and each piece is installed on clients or servers specialized for that subsystem. Client-server is just one approach to managing network applications The primary alternative, peer-to-peer networking, models all devices as having equivalent capability rather than specialized client or server roles. Compared to clientserver, peer to peer networks offer some advantages such as more flexibility in growing the system to handle large number of clients. Client-server networks generally offer advantages in keeping data secure
PEER TO PEER networks
Peer to peer is an approach to computer networking where all computers share equivalent responsibility for processing data. Peer-to-peer networking (also known simply as peer networking) differs from client-server networking, where certain devices have responsibility for providing or "serving" data and other devices consume or otherwise act as "clients" of those servers. Characteristics of a Peer Network Peer to peer networking is common on small local area networks (LANs), particularly home networks. Both wired and wireless home networks can be configured as peer to peer environments. Computers in a peer to peer network run the same networking protocols and software. Peer networks are also often situated physically near to each other, typically in homes, small businesses or schools. Some peer networks, however, utilize the Internet and are geographically dispersed worldwide. Home networks that utilize broadband routers are hybrid peer to peer and client-server environments. The router provides centralized Internet connection sharing, but file, printer and other resource sharing is managed directly between the local computers involved. Peer to Peer and P2P Networks Internet-based peer to peer networks emerged in the 1990s due to the development of P2P file sharing networks like Napster. Technically, many P2P networks (including the original Napster) are not pure peer networks but rather hybrid designs as they utilize central servers for some functions such as search.
OSI MODEL
OSI Model - Upper and Lower Layers Bradley Mitchell
The Open Systems Interconnection (OSI) reference model has been an essential element of computer network design since its ratification in 1984. The OSI is an abstract model of how network protocols and equipment should communicate and work together (interoperate).
The OSI model is a technology standard maintained by the International Standards Organization (ISO). Although today's technologies do not fully conform to the standard, it remains a useful introduction to the study of network architecture. The OSI Model Stack The OSI model divides the complex task of computer-to-computer communications, traditionally called internetworking, into a series of stages known as layers. Layers in the OSI model are ordered from lowest level to highest. Together, these layers comprise the OSI stack. The stack contains seven layers in two groups:
Upper layers 7. application 6. presentation 5. session Lower layers 4. transport 3. network 2. data link 1. physical
More - OSI Model Layers Upper Layers of the OSI Model OSI designates the application, presentation, and session stages of the stack as the upper layers. Generally speaking, software in these layers performs application-specific functions like data formatting, encryption, and connection management. Examples of upper layer technologies in the OSI model are HTTP, SSL and NFS. Lower Layers of the OSI Model The remaining lower layers of the OSI model provide more primitive network-specific functions like routing, addressing, and flow control. Examples of lower layer technologies in the OSI model are TCP, IP, and Ethernet.
TCP and UDP
UDP uses a simple transmission model with a minimum of protocol mechanism.[1] It has no handshaking dialogues, and thus exposes any unreliability of the underlying network protocol to
the user's program. As this is normally IP over unreliable media, there is no guarantee of delivery, ordering or duplicate protection. TCP provides reliable, ordered delivery of a stream of octets from a program on one computer to another program on another computer. TCP is the protocol used by major Internet applications such as the World Wide Web, email, remote administration and file transfer.
DNS & DHCP
DHCP is a protocol known as Dynamic Host Configuration Protocol. Its main purpose is to assign different IP addresses to devices on a network. Network administrator has to assign IP addresses when a user connects to internet through a machine. By using this protocol network administrator's work become easier because he does not have to assign IP addresses manually as using DHCP this process of assigning IP addresses becomes automated. DNS is also a internet protocol and is known as Domain Name Server or Domain Name Service. Its purpose is to translate domain names into IP addresses. Whenever we use a domain name, then a service is used for translating domain names into IP addresses and is known as DNS. For example, the domain name www.bigcity.com might translate to 192.103.202.2. So what DNS did in above example as it translates the name "Bigcity" into corresponding IP address. If one DNS server does not know how to translate the particular domain name it asks another DNS server and this process continued until the correct IP address is returned. As in above example, if one domain server does not know how to translate www.bigcity.com then it will move to another DNS until the corresponding IP address 192.103.202.2 is returned
MAC & IP
Media Access Control address = (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet. Logically, MAC addresses are used in the Media Access Control protocol sub-layer of the OSI reference model. MAC addresses are most often assigned by the manufacturer of a network interface card (NIC) and are stored in its hardware, the card's read-only memory, or some other firmware mechanism.
A Mac address is a 48bit addressing scheme (usually
represented in HEX). There are 8 bits in a bytes therefore it is 6 bytes long.
An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication.[1] An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."[2] The designers of the Internet Protocol defined an IP use today.
address as a 32-bit
number[1] and this system, known as Internet Protocol Version 4 (IPv4), is still in
IP classes:
Subnetwork: A subnetwork, or subnet, is a logically visible subdivision of an IP network.[1] The practice of dividing a network into two or more networks is called subnetting. All computers that belong to a subnet are addressed with a common, identical, mostsignificant bit-group in their IP address. This results in the logical division of an IP address into two fields, a network or routing prefix and the rest field or host identifier. The rest field is an identifier for a specific host or network interface.
ipconfig syntax:
ipconfig [/all] [/renew [Adapter]] [/release [Adapter]] [/flushdns] [/registerdns] [/showclassid Adapter] [/setclassid Adapter [ClassID]] [/displaydns]
Folosind comanda sub forma ipconfig se afiseaza informatii de baza despre configuratia TCP/IP (adresa IP, masca de subretea si gateway-ul), pentru toate placile de retea. /all, afisarea informatiilor complete despre configuratia TCP/IP, pentru toate placile de retea, suplimentar fata de variana precedenta afiseaza setarile DNS (Domain Name System) si WINGS (Windows Internet Naming Service). Comanda ping Programul prin care se implementeaza aceasta comanda a fost creat de Mike Muuss in decembrie 1983, denumirea provine de la sunetul pulsurilor emise de sonarul unui submarin care se reflecta cand intalnesc tinta. Se utilizeaza pentru testarea unei conexiuni la Internet, prin transmiterea de mesaje ICMP (Internet Control Message Protocol) ”echo request”, in traducere solicitare de raspuns, sub forma de pachete de date spre o anumita gazda (TargetName), apoi se asteapta raspunsurile ICMP “echo response”, de la gazda destinatie si se estimeaza durata si rata de pierdere a pachetelor. Sintaxa
ping [-t] [-a] [-n Count] [-l Size] [-f] [-i TTL] [-v TOS] [-r Count] [-s Count] [] [-w Timeout] [TargetName] Testarea unei conexiuni (fig. 7) se realizeaza folosind forma ping [TargetName] unde TargetName este destinatia si poate fi o adesa IP sau o adresa web.
Default Gateway
In computer networking, a gateway is a node (a router) on a TCP/IP network that serves as an access point to another network. A default gateway is the node on the computer network that the network software uses when an IP address does not match any other routes in the routing table. In organizational systems a gateway is a node that routes the traffic from a workstation to another network segment. The default gateway commonly connects the internal networks and the outside network (Internet). In such a situation, the gateway node could also act as a proxy server and a firewall.
ARP
Address Resolution Protocol = resolving the destination IP address into a MAC address through an ARP
Tunneling protocol
By using tunneling one can (for example) carry a payload over an incompatible deliverynetwork, or provide a secure path through an untrusted network. Tunneling protocols may use data encryption to transport insecure payload protocols over a public network (such as the Internet), thereby providing VPN functionality.
HOP COUNT
In computer networking, hop count refers to the intermediate devices (like routers) through which data must pass between source and destination, rather than flowing directly over a single wire.[1] Each router along the data path constitutes a hop, as the data is moved from one Layer 3 network to another. Hop count is therefore a basic measurement of distance in an network.
An illustration of hops in a network. The hop count between the computers in this case is 2.
By itself, hop count is not a useful metric for determining the optimum network path, as it does not take into consideration the speed, load, reliability, or latency of any particular hop, but merely the total count. Nevertheless, some routing protocols such as RIP use hop count as their sole metric.[2] Hop counts are often useful to find faults in a network, or to discover if routing is indeed correct. Network utilities like Ping can be used to determine the hop count to a specific destination. Ping generates packets that include a field reserved for the hop count. Each time a capable device receives these packets, that device modifies the packet, incrementing the hop count by one. In addition, the device compares the hop count against a predetermined limit and discards the packet if its hop count is too high. This prevents packets from endlessly bouncing around the network due to routing errors. Both routers and bridges are capable of managing hop counts, but other types of intermediate devices (like hubs) are not.
The term client-server refers to a popular model for computer networking that utilizes client and server devices each designed for specific purposes. The client-server model can be used on the Internet as well as local area networks (LANs). Examples of client-server systems on the Internet include Web browsers and Web servers, FTP clients and servers, and the DNS. Client and Server Devices Client/server networking grew in popularity many years ago as personal computers (PCs) became the common alternative to older mainframe computers. Client devices are typically PCs with network software applications installed that request and receive information over the network. Mobile devices as well as desktop computers can both function as clients. Client-Server Applications The client-server model distinguishes between applications as well as devices. Network clients make requests to a server by sending messages, and servers respond to their clients by acting on each request and returning results. One server generally supports numerous clients, and multiple servers can be networked together in a pool to handle the increased processing load as the number of clients grows. A client computer and a server computer are usually two separate devices, each customized for their designed purpose. For example, a Web client works best with a large screen display, while a Web server does not need any display at all and can be located anywhere in the world. However, in some cases a given device can function both as a client and a server for the same application. Likewise, a device that is a server for one application can simultaneously act as a client to other servers, for different applications. [Some of the most popular applications on the Internet follow the client-server model including email, FTP and Web services. Each of these clients features a user interface (either graphic- or text-based) and a client application that allows the user to connect to servers. In the case of email and FTP, users enter a computer name (or sometimes an IP address) into the interface to set up connections to the server. Local Client-Server Networks Many home networks utilize client-server systems without even realizing it. Broadband routers, for example, contain DHCP servers that provide IP addresses to the home computers (DHCP clients). Other types of network servers found in home include print servers and backup servers. Client-Server vs Peer-to-Peer and Other Models The client-server model was originally developed to allow more users to share access to database applications. Compared to the mainframe approach, client-server offers improved scalability because connections can be made as needed rather than being fixed. The client-server model also supports modular applications that can make the job of creating software easier. In so-called "two-tier" and "three-tier" types of client-server systems, software applications are separated into modular pieces, and each piece is installed on clients or servers specialized for that subsystem. Client-server is just one approach to managing network applications The primary alternative, peer-to-peer networking, models all devices as having equivalent capability rather than specialized client or server roles. Compared to clientserver, peer to peer networks offer some advantages such as more flexibility in growing the system to handle large number of clients. Client-server networks generally offer advantages in keeping data secure
PEER TO PEER networks
Peer to peer is an approach to computer networking where all computers share equivalent responsibility for processing data. Peer-to-peer networking (also known simply as peer networking) differs from client-server networking, where certain devices have responsibility for providing or "serving" data and other devices consume or otherwise act as "clients" of those servers. Characteristics of a Peer Network Peer to peer networking is common on small local area networks (LANs), particularly home networks. Both wired and wireless home networks can be configured as peer to peer environments. Computers in a peer to peer network run the same networking protocols and software. Peer networks are also often situated physically near to each other, typically in homes, small businesses or schools. Some peer networks, however, utilize the Internet and are geographically dispersed worldwide. Home networks that utilize broadband routers are hybrid peer to peer and client-server environments. The router provides centralized Internet connection sharing, but file, printer and other resource sharing is managed directly between the local computers involved. Peer to Peer and P2P Networks Internet-based peer to peer networks emerged in the 1990s due to the development of P2P file sharing networks like Napster. Technically, many P2P networks (including the original Napster) are not pure peer networks but rather hybrid designs as they utilize central servers for some functions such as search.
OSI MODEL
OSI Model - Upper and Lower Layers Bradley Mitchell
The Open Systems Interconnection (OSI) reference model has been an essential element of computer network design since its ratification in 1984. The OSI is an abstract model of how network protocols and equipment should communicate and work together (interoperate).
The OSI model is a technology standard maintained by the International Standards Organization (ISO). Although today's technologies do not fully conform to the standard, it remains a useful introduction to the study of network architecture. The OSI Model Stack The OSI model divides the complex task of computer-to-computer communications, traditionally called internetworking, into a series of stages known as layers. Layers in the OSI model are ordered from lowest level to highest. Together, these layers comprise the OSI stack. The stack contains seven layers in two groups:
Upper layers 7. application 6. presentation 5. session Lower layers 4. transport 3. network 2. data link 1. physical
More - OSI Model Layers Upper Layers of the OSI Model OSI designates the application, presentation, and session stages of the stack as the upper layers. Generally speaking, software in these layers performs application-specific functions like data formatting, encryption, and connection management. Examples of upper layer technologies in the OSI model are HTTP, SSL and NFS. Lower Layers of the OSI Model The remaining lower layers of the OSI model provide more primitive network-specific functions like routing, addressing, and flow control. Examples of lower layer technologies in the OSI model are TCP, IP, and Ethernet.
TCP and UDP
UDP uses a simple transmission model with a minimum of protocol mechanism.[1] It has no handshaking dialogues, and thus exposes any unreliability of the underlying network protocol to
the user's program. As this is normally IP over unreliable media, there is no guarantee of delivery, ordering or duplicate protection. TCP provides reliable, ordered delivery of a stream of octets from a program on one computer to another program on another computer. TCP is the protocol used by major Internet applications such as the World Wide Web, email, remote administration and file transfer.
DNS & DHCP
DHCP is a protocol known as Dynamic Host Configuration Protocol. Its main purpose is to assign different IP addresses to devices on a network. Network administrator has to assign IP addresses when a user connects to internet through a machine. By using this protocol network administrator's work become easier because he does not have to assign IP addresses manually as using DHCP this process of assigning IP addresses becomes automated. DNS is also a internet protocol and is known as Domain Name Server or Domain Name Service. Its purpose is to translate domain names into IP addresses. Whenever we use a domain name, then a service is used for translating domain names into IP addresses and is known as DNS. For example, the domain name www.bigcity.com might translate to 192.103.202.2. So what DNS did in above example as it translates the name "Bigcity" into corresponding IP address. If one DNS server does not know how to translate the particular domain name it asks another DNS server and this process continued until the correct IP address is returned. As in above example, if one domain server does not know how to translate www.bigcity.com then it will move to another DNS until the corresponding IP address 192.103.202.2 is returned
MAC & IP
Media Access Control address = (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet. Logically, MAC addresses are used in the Media Access Control protocol sub-layer of the OSI reference model. MAC addresses are most often assigned by the manufacturer of a network interface card (NIC) and are stored in its hardware, the card's read-only memory, or some other firmware mechanism.
A Mac address is a 48bit addressing scheme (usually
represented in HEX). There are 8 bits in a bytes therefore it is 6 bytes long.
An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication.[1] An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."[2] The designers of the Internet Protocol defined an IP use today.
address as a 32-bit
number[1] and this system, known as Internet Protocol Version 4 (IPv4), is still in
IP classes:
Subnetwork: A subnetwork, or subnet, is a logically visible subdivision of an IP network.[1] The practice of dividing a network into two or more networks is called subnetting. All computers that belong to a subnet are addressed with a common, identical, mostsignificant bit-group in their IP address. This results in the logical division of an IP address into two fields, a network or routing prefix and the rest field or host identifier. The rest field is an identifier for a specific host or network interface.
ipconfig syntax:
ipconfig [/all] [/renew [Adapter]] [/release [Adapter]] [/flushdns] [/registerdns] [/showclassid Adapter] [/setclassid Adapter [ClassID]] [/displaydns]
Folosind comanda sub forma ipconfig se afiseaza informatii de baza despre configuratia TCP/IP (adresa IP, masca de subretea si gateway-ul), pentru toate placile de retea. /all, afisarea informatiilor complete despre configuratia TCP/IP, pentru toate placile de retea, suplimentar fata de variana precedenta afiseaza setarile DNS (Domain Name System) si WINGS (Windows Internet Naming Service). Comanda ping Programul prin care se implementeaza aceasta comanda a fost creat de Mike Muuss in decembrie 1983, denumirea provine de la sunetul pulsurilor emise de sonarul unui submarin care se reflecta cand intalnesc tinta. Se utilizeaza pentru testarea unei conexiuni la Internet, prin transmiterea de mesaje ICMP (Internet Control Message Protocol) ”echo request”, in traducere solicitare de raspuns, sub forma de pachete de date spre o anumita gazda (TargetName), apoi se asteapta raspunsurile ICMP “echo response”, de la gazda destinatie si se estimeaza durata si rata de pierdere a pachetelor. Sintaxa
ping [-t] [-a] [-n Count] [-l Size] [-f] [-i TTL] [-v TOS] [-r Count] [-s Count] [] [-w Timeout] [TargetName] Testarea unei conexiuni (fig. 7) se realizeaza folosind forma ping [TargetName] unde TargetName este destinatia si poate fi o adesa IP sau o adresa web.
Default Gateway
In computer networking, a gateway is a node (a router) on a TCP/IP network that serves as an access point to another network. A default gateway is the node on the computer network that the network software uses when an IP address does not match any other routes in the routing table. In organizational systems a gateway is a node that routes the traffic from a workstation to another network segment. The default gateway commonly connects the internal networks and the outside network (Internet). In such a situation, the gateway node could also act as a proxy server and a firewall.
ARP
Address Resolution Protocol = resolving the destination IP address into a MAC address through an ARP
Tunneling protocol
By using tunneling one can (for example) carry a payload over an incompatible deliverynetwork, or provide a secure path through an untrusted network. Tunneling protocols may use data encryption to transport insecure payload protocols over a public network (such as the Internet), thereby providing VPN functionality.
HOP COUNT
In computer networking, hop count refers to the intermediate devices (like routers) through which data must pass between source and destination, rather than flowing directly over a single wire.[1] Each router along the data path constitutes a hop, as the data is moved from one Layer 3 network to another. Hop count is therefore a basic measurement of distance in an network.
An illustration of hops in a network. The hop count between the computers in this case is 2.
By itself, hop count is not a useful metric for determining the optimum network path, as it does not take into consideration the speed, load, reliability, or latency of any particular hop, but merely the total count. Nevertheless, some routing protocols such as RIP use hop count as their sole metric.[2] Hop counts are often useful to find faults in a network, or to discover if routing is indeed correct. Network utilities like Ping can be used to determine the hop count to a specific destination. Ping generates packets that include a field reserved for the hop count. Each time a capable device receives these packets, that device modifies the packet, incrementing the hop count by one. In addition, the device compares the hop count against a predetermined limit and discards the packet if its hop count is too high. This prevents packets from endlessly bouncing around the network due to routing errors. Both routers and bridges are capable of managing hop counts, but other types of intermediate devices (like hubs) are not.
