BRIDGE

"A device used to connect two separate Ethernet networks into one extended Ethernet. Bridges only forward packets between networks that are destined for the other network. Term used by Novell to denote a computer that accepts packets at the network layer and forward them to another network."

 

Why Use Bridges?

Bridges are important in some network because the networks are geographically divided into many parts. Something is required to join these networks so that we can connect the whole network. Take for example LAN, if there is no medium to join these LAN an enterprise may be limited in its growth potential. The bridge is one of the tools to join these LANS.

Secondly LAN (for example Ethernet) can be limited in its distance. We can eliminate this problem using bridges so that we can connect the network within the building or campus using bridges. The geographically challenged networks can be connected using Bridges.

Third, the network administrator can control the amount of traffic going through bridges sent across the expensive network media.

Fourth, the bridge is plug and play device so there is no need to configure bridge. And suppose any machine was taken out from the network then there is no need for network administrator to update the information as bridges are self configured.

 

Types of Bridges

• Transparent basic bridge
  
• Source routing bridge
  
• Transparent learning bridge
  
• Transparent spanning bridge
  

 

 

 

 

ROUTER

This article is about a computer networking device. For the kind of rotating cutting tool, see wood router. For the type of network router found in many homes, see DSL router.

A router is a device that extracts the destination of a packet it receives, selects the best path to that destination, and forwards data packets to the next device along this path.[1] They connect networks together; a LAN to a WAN for example, to access the Internet. Some units, like the Cisco 1800 (pictured), are available in both wired and wireless models.

Function:

A more precise definition of a router is a computer networking device that interconnects separate logical subnets. Routers are now available in many types, though all are fundamentally doing the same job. A router is a computer whose software and hardware are usually tailored to the tasks of routing and forwarding, generally containing a specialized operating system (e.g. Cisco's IOS or Juniper Networks JunOS or Extreme Networks XOS), RAM, NVRAM, flash memory, and one or more processors. High-end routers contain many processors and specialized Application-specific integrated circuits (ASIC) and do a great deal of parallel processing. Chassis based systems like the Nortel MERS-8600 or ERS-8600 routing switch, have multiple ASICs on every module and allow for a wide variety of LAN, MAN, METRO, and WAN port technologies or other connections that are customizable.

 

 

 

 

GATEWAY

A gateway, in computer networking technology, is a node that serves as an entrance to another network, and vice-versa. Gateways are most commonly used to transfer data between private networks and the Internet.

A gateway is a network point that acts as an entrance to another network. On the Internet, a node or stopping point can be either a gateway node or a host (end-point) node. Both the computers of Internet users and the computers that serve pages to users are host nodes. The computers that control traffic within your company's network or at your local Internet service provider (ISP) are gateway nodes. In the network for an enterprise, a computer server acting as a gateway node is often also acting as a proxy server and a firewall server. A gateway is often associated with both a router, which knows where to direct a given packet of data that arrives at the gateway, and a switch, which furnishes the actual path in and out of the gateway for a given packet.

On an IP network, clients should automatically send IP packets with a destination outside a given subnet mask to a network gateway. A subnet mask defines the IP range of a network. For example, if a network has a base IP address of 192.168.0.0 and has a subnet mask of 255.255.255.0, then any data going to an IP address outside of 192.168.0.X will be sent to that network's gateway. While forwarding an IP packet to another network, the gateway might or might not perform Network Address Translation.

A gateway is an essential feature of most routers, although other devices (such as any PC or server) can function as a gateway.

Most computer operating systems use the terms described above. A computer running Microsoft Windows however describes this standard networking feature as Internet Connection Sharing; which will act as a gateway, offering a connection between the Internet and an internal network. Such a system might also act as a DHCP server.

Gateway computers: Enable connection from one network, eg: from a LAN to a WAN. Whenever you login to a LAN i.e. connect to the LAN's network server and then access the Internet, you are utilizing a gateway.

 

 

 

INTERNET

The Internet is a worldwide, publicly accessible series of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP). It is a "network of networks" that consists of millions of smaller domestic, academic, business, and government networks, which together carry various information and services, such as electronic mail, online chat, file transfer, and the interlinked web pages and other resources of the World Wide Web.

 

 

EXTRANET

An extranet is a private network that uses Internet protocols, network connectivity, and possibly the public telecommunication system to securely share part of an organization's information or operations with suppliers, vendors, partners, customers or other businesses. An extranet can be viewed as part of a company's Intranet that is extended to users outside the company (e.g.: normally over the Internet). It has also been described as a "state of mind" in which the Internet is perceived as a way to do business with a preapproved set of other companies business-to-business (B2B), in isolation from all other Internet users. In contrast, business-to-consumer (B2C) involves known server(s) of one or more companies, communicating with previously unknown consumer users.

Briefly, an extranet can be understood as a private intranet mapped onto the Internet or some other transmission system not accessible to the general public, but is managed by more than one company's administrator(s). For example, military networks of different security levels may map onto a common military radio transmission system that never connects to the Internet. Any private network mapped onto a public one is a virtual private network (VPN). In contrast, an intranet is a VPN under the control of a single company's administrator(s).

 

An argument has been made that "extranet" is just a buzzword for describing what institutions have been doing for decades, that is, interconnecting to each other to create private networks for sharing information. One of the differences that characterized an extranet, however, is that its interconnections are over a shared network rather than through dedicated physical lines. With respect to Internet Protocol networks, RFC 2547 states "If all the sites in a VPN are owned by the same enterprise, the VPN is a corporate intranet. If the various sites in a VPN are owned by different enterprises, the VPN is an extranet. A site can be in more than one VPN; e.g., in an intranet and several extranets. We regard both intranets and extranets as VPNs. In general, when we use the term VPN we will not be distinguishing between intranets and extranets. Even if this argument is valid, the term "extranet" is still applied and can be used to eliminate the use of the above description."

Another very common use of the term "extranet" is to designate the "private part" of a website, where "registered users" can navigate, enabled by authentication mechanisms on a "login page".

An extranet requires security and privacy. These can include firewalls, server management, the issuance and use of digital certificates or similar means of user authentication, encryption of messages, and the use of virtual private networks (VPNs) that tunnel through the public network.

 

 

 

 

IP ADDRESS (INTERNET PROTOCOL ADDRESS)

An IP address (Internet Protocol address) is a unique address that certain electronic devices use in order to identify and communicate with each other on a computer network utilizing the Internet Protocol standard (IP)—in simpler terms, a computer address. Any participating network device—including routers, switches, computers, infrastructure servers (e.g., NTP, DNS, DHCP, SNMP, etc.), printers, Internet fax machines, and some telephones—can have their own address that is unique within the scope of the specific network. Some IP addresses are intended to be unique within the scope of the global Internet, while others need to be unique only within the scope of an enterprise.

 

In other words, the IP address acts as a locator for one IP device to find another and interact with it. It is not intended, however, to act as an identifier that always uniquely identifies a particular device.

 

An IP address can also be thought of as the equivalent of a street address or a phone number (compare: VoIP (voice over (the) internet protocol)) for a computer or other network device on the Internet. Just as each street address and phone number uniquely identifies a building or telephone, an IP address can uniquely identify a specific computer or other network device on a network. An IP address differs from other contact information, however, because the linkage of a user's IP address to his/her name is not publicly available information.

 

Further, an IP address is not necessarily linked, in a persistent way, to a physical location or even data link layer address. In the past, an IP address could be considered a unique identifier of a particular IP host, in addition to being a locator. When it was usable as an identifier, it was static, and it was assumed to be globally unique from end to end of the Internet.

 

In current practice, an IP address is less likely to be an identifier, due to technologies such as:

Dynamic assignment, as with an address that is assigned by the access device by which the user's host connects over a dialup telephone line or by a set-top box for an IP over cable network. However the network provider maintains a database of which IP address was assigned to which access port on dialup, or MAC address on LANs or broadband networks. This information, assuming it is available to the investigator, may help to identify the computer, although that is unlikely if it was a dialup connection where the identifier is of the dial-in port, not the computer itself. More extensive forensic work, with access to telephone records, may identify the calling telephone, although that may itself be a "cutout" on the way to the real telephone.

Network address translation (or NAT), a feature common on gateway routers in corporate networks or home LANs, where the address visible to the Internet is the "outside" of a device that maps it to a completely different and hidden address on the "inside".

 

 

 

SUBNETWORK/SUBNETTING

In computer networks which use the Internet Protocol, a subnetwork or subnet is a range of logical addresses within the address space that is assigned to an organization. Subnetting is a hierarchical partitioning of the network address space of an organization (and of the network nodes of an autonomous system) into several subnets. Routers constitute borders between subnets. Communication to and from a subnet is mediated by one specific port of one specific router, at least momentarily.

A typical subnet is a physical network served by one router, for instance an Ethernet network (consisting of one or several Ethernet segments or local area networks, interconnected by network switches and network bridges) or a Virtual Local Area Network (VLAN). However, subnetting allows the network to be logically divided regardless of the physical layout of a network, since it is possible to divide a physical network into several subnets by configuring different host computers to use different routers.

The address to all nodes in a subnet starts with the same binary sequence, which is its network id and subnet id. In IPv4, the subnet is identified by its base address and subnet mask. The CIDR-style prefix notation (e.g., /24) is functionally equivalent to a subnet mask, and generally easier to understand.

Subnetting simplifies routing, since each locally connected subnet typically is represented by one row in the routing tables in each connected router. More distant sets of contiguous subnets are more likely to be represented by a row of the routing table that corresponds to the aggregated block.

Subnetting was originally introduced before the introduction of classful network addresses in IPv4, to allow a single larger network to have a number of smaller networks within it, controlled by several routers. Subnetting made Classless Inter-Domain Routing possible.

In order for computers to communicate in a routing domain with one or many subnets, they will all need their own IP address. However, if you need more than one logical block of addresses, subnetting provides the ability to easily divide one IP address range amongst all the hosts in your network. Subnetting is used in IP networks to break up larger network prefixes into a smaller network. Subnetting involves manually calculating the bits of an IP address and taking them from the host side of bits and adding them to the routing prefix side.

 

 

SUPERNETTING

Supernetting is synonymous with Classless Inter-Domain Routing (CIDR) although CIDR is rather just the concept that is implemented when subnetting or supernetting.

In Internet networking terminology, a supernet is a block of contiguous subnetworks addressed as a single subnet.

Supernetting alleviates some of the issues with the original classful addressing scheme for IP addresses by allowing multiple networks address ranges to be combined, either to create a single larger network, or just for route aggregation to keep the "Internet Routing Table" (or any routing table) from growing too large.

For supernetting to work, you must be using static routing everywhere or be using a routing protocol which supports classless routing, such as RIPv2 or OSPF (or BGP for Exterior Routing) which can carry subnet mask information with the routing update. The older RIPv1 (or EGP for Exterior Routing) protocol only understands classful addressing, and therefore cannot transmit subnet mask information.

 

 

 

 

NETWORK ADDRESS AND LOGICAL ADDRESS

The term network address sometimes refers to logical address, i.e. network layer address such as the IP address, and sometimes to the first address (the base address) of a classful address range to an organization.

Computers and devices that are part of an internetworking network such as the Internet all have a logical address. The network address is unique to that device and can either be dynamically or statically configured. This address allows the device to communicate with other devices connected to the network. The most common network addressing scheme is IPv4. The IPv4 network address consists of a 32 bit address written, for human readability, into 4 octets and a subnet mask of like size. In order to facilitate the routing process the address is divided into two pieces, the network prefix length that is significant for routing decisions at that particular topological point, and the remaining don't care bits. A host address is meaningful only when on the subnet where that host resides. This works much like a postal address where the higher order part of the network prefix (e.g., /18)would represent the city, the full prefix (e.g., /26) and the host address (i.e., the remaining six bits) would represent the address of a specific house on that street. The subnet mask or CIDR prefix address is used in conjunction with the network address to determine which part of the address is the network address and which part is the host address.

 

 

 

IP DATAGRAM FORMAT

• Formally, the unit of IP data delivery is called a datagram
  
• Includes header area and data area
  
• Datagrams can have different sizes
  
  • Header area usually fixed (20 octets) but can have options
    
  • Data area can contain between 1 octet and 65,535 octets (2¹⁶ - 1)
    
  • Usually, data area much larger than header
    

Forwarding datagrams

• Header contains all information needed to deliver datagram to destination computer
  
  • Destination address
    
  • Source address
    
  • Identifier
    
  • Other delivery information
    
• Router examines header of each datagram and forwards datagram along path to destination
  

 

IP datagram header fields

VERS - version of IP (currently 4)

H. LEN - header length (in units of 32 bits)

SERVICE TYPE - sender's preference for low latency, high reliability (rarely used)

TOTAL LENGTH - total octets in datagram

IDENT, FLAGS, FRAGMENT OFFSET - used with fragmentation

TTL - time to live; decremented in each router; datagram discarded when TTL = 0

TYPE - type of protocol carried in datagram; e.g., TCP, UDP

HEADER CHECKSUM - 1s complement of 1s complement sum

SOURCE, DEST IP ADDRESS - IP addresses of original source and ultimate destination