what are network layers?
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ISO/OSI Network Model\nThe standard model for networking protocols and distributed applications is the International Standard Organization's Open System Interconnect (ISO/OSI) model. It defines seven network layers. \n\nLayer 1 - Physical \nPhysical layer defines the cable or physical medium itself, e.g., thinnet, thicknet, unshielded twisted pairs (UTP). All media are functionally equivalent. The main difference is in convenience and cost of installation and maintenance. Converters from one media to another operate at this level. \n\nLayer 2 - Data Link \nData Link layer defines the format of data on the network. A network data frame, aka packet, includes checksum, source and destination address, and data. The largest packet that can be sent through a data link layer defines the Maximum Transmission Unit (MTU). The data link layer handles the physical and logical connections to the packet's destination, using a network interface. A host connected to an Ethernet would have an Ethernet interface to handle connections to the outside world, and a loopback interface to send packets to itself. \n\nEthernet addresses a host using a unique, 48-bit address called its Ethernet address or Media Access Control (MAC) address. MAC addresses are usually represented as six colon-separated pairs of hex digits, e.g., 8:0:20:11:ac:85. This number is unique and is associated with a particular Ethernet device. Hosts with multiple network interfaces should use the same MAC address on each. The data link layer's protocol-specific header specifies the MAC address of the packet's source and destination. When a packet is sent to all hosts (broadcast), a special MAC address (ff:ff:ff:ff:ff:ff) is used. \n\nLayer 3 - Network \nNFS uses Internetwork Protocol (IP) as its network layer interface. IP is responsible for routing, directing datagrams from one network to another. The network layer may have to break large datagrams, larger than MTU, into smaller packets and host receiving the packet will have to reassemble the fragmented datagram. The Internetwork Protocol identifies each host with a 32-bit IP address. IP addresses are written as four dot-separated decimal numbers between 0 and 255, e.g., 129.79.16.40. The leading 1-3 bytes of the IP identify the network and the remaining bytes identifies the host on that network. The network portion of the IP is assigned by InterNIC Registration Services, under the contract to the National Science Foundation, and the host portion of the IP is assigned by the local network administrators, locally by noc@indiana.edu. For large sites, usually subnetted like ours, the first two bytes represents the network portion of the IP, and the third and fourth bytes identify the subnet and host respectively. \n\nEven though IP packets are addressed using IP addresses, hardware addresses must be used to actually transport data from one host to another. The Address Resolution Protocol (ARP) is used to map the IP address to it hardware address. \n\nLayer 4 - Transport \nTransport layer subdivides user-buffer into network-buffer sized datagrams and enforces desired transmission control. Two transport protocols, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP), sits at the transport layer. Reliability and speed are the primary difference between these two protocols. TCP establishes connections between two hosts on the network through 'sockets' which are determined by the IP address and port number. TCP keeps track of the packet delivery order and the packets that must be resent. Maintaining this information for each connection makes TCP a stateful protocol. UDP on the other hand provides a low overhead transmission service, but with less error checking. NFS is built on top of UDP because of its speed and statelessness. Statelessness simplifies the crash recovery. \n\nLayer 5 - Session \nThe session protocol defines the format of the data sent over the connections. The NFS uses the Remote
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Networking is the scientific and engineering discipline concerned with communication between computer systems. Such networks involve at least two computers separated by a few inches(eg: LAN, Bluetooth) or thousands of miles (e.g. Internet, Wifi). Computer networking is sometimes considered a sub-discipline of telecommunications.
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A hub connects computers, but sends all traffic to all ports which results in network collisions.  \n\nA switch is like a hub, but smarter.  It keeps track of which computer asks for which piece of data and has far less collisions, if any.  Switches that are for home users are only slightly more expensive than hubs.\n\nA router is like a switch, but also can assign ip addresses, forward network traffic coming in on a certain port to a certain ip address, block certain ports, etc.  \n\nA network bridge merges, for lack of a better word, two network connections on a computer.  Honestly I haven't ever needed a network bridge so I can't say much about them.
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The application layer of TCP/IP is the layer where applications gain access. There are many standards TCP/IP utilities and services at the Applications layer such as FTP, Telnet, SNMP and DNS. \nMicrosoft TCP/IP provides two interfaces for network applications. Windows sockets-standard application programming interface (API) under Microsoft Windows for transport protocols such as TCP/IP and IPX.
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a computer network is a series of computer connected that can share resources.\n\nA group of computers, connected by a telecommunications link, that share information
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(VPN) The use of encryption in the lower protocol layers to provide a secure connection through an otherwise insecure network, typically the Internet. VPNs are generally cheaper than real private networks using private lines but rely on having the same encryption system at both ends. The encryption may be performed by firewall software or possibly by routers.\n\nLink-level (layer 2 and 3) encryption provides extra protection by encrypting all of each datagram except the link-level information. This prevents a listener from obtaining information about network structure. While link-level encryption prevents traffic analysis (a form of attack), it must encrypt/decrypt on every hop and every path.\n\nProtocol-level encryption (layer 3 and 4) encryption encrypts protocol data but leaves protocol and link headers clear. While protocol-level encryption requires you to encrypt/decrypt data only once, and it encrypts/decrypts only those sessions that need it, headers are sent as clear text, allowing traffic analysis.\n\nApplication (layer 5 up) encryption is based on a particular application and requires that the application be modified to incorporate encryption.
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if you are useing windows open the command prompt(u can do this by typing 'cmd' on the Run command box). Then in the command prompt type ipconfig.It gives ur network details including IP, gateway etc..
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A layer 3 switch will switch packets faster than a traditional router because the packet switching is done in hardware as opposed to being done in software.  \n\nThat said, if you have these servers all on the same network/subnet, you don't need either one.  Just a fast layer 2 switch.  \n\nBut if you are going to have to jump between networks/subnetworks where a router would normally be required, a layer 3 switch (a fast one) is the way to go.
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They are not mutually exclusive.  All organizations should have external firewalls, those should be backed by departmental firewalls, and those should be backed by firewalls on individual hosts.  Layered security is a time-tested and well proven model.  Never put all of your information security eggs in one basket.
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Router:\nA router is a computer networking device that forwards data packets across an internetwork toward their destinations, through a process known as routing. Routing occurs at layer 3 (the Network layer) of the OSI seven-layer model.
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A network bridge connects multiple network segments (network domains) along the data link layer. It is sometimes called a network switch, and it works by using bridging. Traffic from one network is forwarded through it to another network. The bridge simply does what its name entails, by connecting two sides from adjacent networks.\n\nA repeater is a similar device that connects network segments at the physical layer. An Ethernet hub is a type of repeater.\n\nIn Ethernets, the term "bridge" formally means a device that behaves according to the IEEE 802.1D standard - this is most often referred to as a network switch in marketing literature.
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http://technology.monster.com/articles/networkengineer/\n\nGood luck to you!
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N.\n\nhttp://www.harveycartel.org/metanet/n.html
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Its a set of rules.Like u hav the IP protocol that specifies the format in the internet layer
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NOCs \n\nNetwork Operations Center (NOC) \n\n\n\nInternet2 is a consortium being led by 207 universities working in partnership with industry and government to develop and deploy advanced network applications and technologies, accelerating the creation of tomorrow's Internet. Internet2 is recreating the partnership among academia, industry and government that fostered today´s Internet in its infancy. The primary goals of Internet2 are to: \n\nCreate a leading edge network capability for the national research community \nEnable revolutionary Internet applications \nEnsure the rapid transfer of new network services and applications to the broader Internet community.
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Interconnecting devices which are routers, provide a transit for the traffic, hosts serve as end sytstems and servers serve the end systems.\n\nThats the Basic INTERNET !
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A CISCO (or any other router) is a computer networking device that forwards data packets across an internetwork toward their destinations, through a process known as routing. Routing occurs at layer 3 (the Network layer e.g. IP) of the OSI seven-layer protocol stack.