Tuesday 25 October 2011

Networking Tutorials Overview



Find computer network tutorials, wireless communication guide, LAN/WAN guide, local area network tools, wan introduction, osi layers model and many other advance topics of data communication. This is very informative site for the IT people specially in the field of computer networking. You will also find data communication overview, tech guides , data communication related information, topologies, tech study guide, Router Labs, IT certifications, Ethernet guide, free IT resources, ip addressing tools, telecommunication guide and many other informative resources. Data communication is a process of sharing data and shared resources between two or more connected computers. The shared resources can include printer, Fax modem, Hard disk, CD/DVD Rom, Database and the data files.
A computer network can be divided into a small segments called Local Area Network (LAN), networking between computers in a building of a office, medium sized networks (MAN), communication between two offices in a city and wide area networks (WAN) networking between the computers, one is locally placed and the other can be thousands of miles away in another city or another country in the world.

Monday 14 March 2011

Static IP address setup

Static IP address setup
Converting  from a DHCP based LAN configuration
(made easy!)


DHCP Servers automate the process of setting up the 'IP Schema' of your home network. When your computer is turned on, it seeks a DHCP server on the network and gets a 'dynamic' IP address. Each time the computer is turned on, it could get a different IP address depending on a bunch of other factors. Usually your Internet connection sharing solution is responsible for having a DHCP server built in. All broadband routers come with DHCP Servers and almost every software solution like Microsoft Internet Connection Sharing (ICS) does too.
To see your current IP address, go to a command prompt and type IPCONFIG
DHCP Servers and Advanced Applications
The primary reason for switching from a DYNAMIC (DHCP) addressing schema to a static one is the ability to run servers and other advanced applications behind a NAT firewall. When you run any kind of server, a hole must be punched in your firewall and pointed at the computer with the server running - this is called port forwarding. If the IP address of the server changes, the hole will be pointing to the wrong place!
Static IP address' require a small amount of configuration and management up front for a small network but allow the reliable configuration of game and application servers.
INSTRUCTIONS
Side Note:
an IP address is composed of 4 octets, each ranging between 0 and 255. A zero is never used in the first or last octet.

IP Ranges
There are three 'ranges' that are deemed private and are usable for home networks. They are as follows.
192.168.x.x
172.16.x.x
10.x.x.x

The most popular IP address schema set as the default schema is 192.168.x.x, often 192.168.10.x or often 192.168.1.x. Routers and other internet sharing solutions are usually positioned as the first IP address in the schema - in our example it will be 192.168.10.1.
First go to your router's administration page and configure the built in DHCP server. Each router will be a little different and hay have different capabilities. You should leave the DHCP server enabled, but limit the number of IP address it can distribute.
If we allow our DHCP server to start numbering computers at 192.168.10.2 and allow 50 IP address, the last DHCP reserved address will be 192.168.10.52. Sometimes this is done as a 'range' instead of a 'number of computers' setting. To make it easy on ourselves, we might want to start numbering static addressed computers at 192.168.10.100 - well out of the DHCP Range








Our IP schema looks like this
192.168.10.0 subnet 255.255.255.0 is our 'network'.
192.168.10.1 is our router
192.168.10.2 to .52 are DHCP reserved address
192.168.10.100 to .255 are the STATIC address
Setting up a computer:
When we change a computer from DHCP to Static IP, we must type in FOUR pieces of information. IP address, Subnet, Default Gateway, and DNS Server. The IP address will be one from our static IP range, the subnet will be 255.255.255.0 and the Gateway and DNS will be the address of our router - 192.168.10.1
Get the TCP/IP properties of your computer and set them up with the four required pieces of information.
Computer 1
IP: 192.168.10.100
Subnet: 255.255.255.0
Gateway: 192.168.10.1
DNS: 192.168.10.1
Computer 2
IP: 192.168.10.101
Subnet: 255.255.255.0
Gateway: 192.168.10.1
DNS: 192.168.10.1
ADVANCED CONFIGUTATION
Sometimes is necessary or even just beneficial to move your IP schema away from the default that your router comes with. For instance, instead of running the default 192.168.1.0 subnet, you might want to change the third octet to something else. I do this with ALL the networks I set up for both security and routing purposes.
First, pick an third octet - choose something between 11 and 255, anything below 11 is fairly common.
Next, set the internal LAN IP ADDRESS of your ROUTER using the router's administration pages. Next, set your computer up with a STATIC address in that same range and reboot both machines (not necessary to reboot Win2k or WinXP). Lastly, ensure that the DHCP range in your router is set up correctly. Remember, the administration screens are at the NEW router address, not the old one.


ADVANCED CONFIGUTATION
Sometimes is necessary or even just beneficial to move your IP schema away from the default that your router comes with. For instance, instead of running the default 192.168.1.0 subnet, you might want to change the third octet to something else. I do this with ALL the networks I set up for both security and routing purposes.
First, pick an third octet - choose something between 11 and 255, anything below 11 is fairly common.
Next, set the internal LAN IP ADDRESS of your ROUTER using the router's administration pages. Next, set your computer up with a STATIC address in that same range and reboot both machines (not necessary to reboot Win2k or WinXP). Lastly, ensure that the DHCP range in your router is set up correctly. Remember, the administration screens are at the NEW router address, not the old one.

Dynamic vs Static Network Configuration

A guest researcher today called us, because his laptop with Fedora Core 4 didn’t get any working IP address. That problem was solved quite quickly: The “Internet Connection Wizard” didn’t allow him to choose a dynamic configuration via DHCP. It was greyed out and the static configuration was one for a private 192.168.* network.
I quickly found out, that “Network Device Control” allowed us to switch to DHCP. After deleting /etc/resolv.conf, it also got the right DNS servers.
But whatever I restarted, it didn’t set a default route although it did get one by DHCP and had it documented in its lease file.
After about one and a half hour of debugging configurations and network configuration scripts I found out, that if the environment variable $GATEWAY is set, it ignores the one given by DHCP. Then I grepped for GATEWAY in the config file. But I just found the default gateway configured for the old, now greyed out static IP configuration.
Although I told myself “No, it can’t be!” I commented out the default gateway of the now unused static configuration. And yes, I wasn’t mistrustful enough about Fedora: It worked. You really have to change parts of the not selected static IP configuration to make the selected dynamic one to work.
Thanks, Fedora! *bangingtheheadontothetable*

Dynamic network analysis


Dynamic network analysis (DNA) is an emergent scientific field that brings together traditional social network analysis (SNA), link analysis (LA) and multi-agent systems (MAS) within network science and network theory. There are two aspects of this field. The first is the statistical analysis of DNA data. The second is the utilization of simulation to address issues of network dynamics. DNA networks vary from traditional social networks in that they are larger, dynamic, multi-mode, multi-plex networks, and may contain varying levels of uncertainty. The main difference of DNA to SNA is DNA taken the domain of time into account. One of the most notable and earliest case of the use of DNA is in Sampson's monastery study, where he took snapshots of the same network from different intervals and observed and analyzed the evolution of the network.[1]
DNA statistical tools are generally optimized for large-scale networks and admit the analysis of multiple networks simultaneously in which, there are multiple types of nodes (multi-node) and multiple types of links (multi-plex). In contrast, SNA statistical tools focus on single or at most two mode data and facilitate the analysis of only one type of link at a time.
DNA statistical tools tend to provide more measures to the user, because they have measures that use data drawn from multiple networks simultaneously. From a computer simulation perspective, nodes in DNA are like atoms in quantum theory, nodes can be, though need not be, treated as probabilistic. Whereas nodes in a traditional SNA model are static, nodes in a DNA model have the ability to learn. Properties change over time; nodes can adapt: A company's employees can learn new skills and increase their value to the network; Or, capture one terrorist and three more are forced to improvise. Change propagates from one node to the next and so on. DNA adds the element of a network's evolution and considers the circumstances under which change is likely to occur.


Thursday 10 March 2011

Network security

Network security
The main issue with wireless network security is its simplified access to the network compared to traditional wired networks such as ethernet.[citation needed] With wired networking one must either gain access to a building (physically connecting into the internal network) or break through an external firewall. Most business networks protect sensitive data and systems by attempting to disallow external access. Enabling wireless connectivity provides an attack vector, particularly if the network uses inadequate or no encryption.[40]
An attacker who has gained access to a Wi-Fi network router can initiate a DNS spoofing attack against any other user of the network by forging a response before the queried DNS server has a chance to reply.[41]
[edit] Securing methodsA common but unproductive measure to deter unauthorized users involves suppressing the access point's SSID broadcast. This is ineffective as a security method because the SSID is broadcast in the clear in response to a client SSID query. Another unproductive method is to only allow computers with known MAC addresses to join the network.[42] But intruders can defeat this method because they can often (though not always) set MAC addresses with minimal effort (MAC spoofing). If eavesdroppers have the ability to change their MAC address, then they may join the network by spoofing an authorized address.
Wired Equivalent Privacy (WEP) encryption was designed to protect against casual snooping, but is now deprecated. Tools such as AirSnort or Aircrack-ng can quickly recover WEP encryption keys. Once it has seen 5-10 million encrypted packets, AirSnort can determine the encryption password in under a second;[43] newer tools such as aircrack-ptw can use Klein's attack to crack a WEP key with a 50% success rate using only 40,000 packets.
To counteract this in 2002, the Wi-Fi Alliance approved Wi-Fi Protected Access (WPA) which uses TKIP as a stopgap solution for legacy equipment. Though more secure than WEP, it has outlived its designed lifetime and has known attack vectors.
In 2004, the IEEE ratified the full IEEE 802.11i (WPA2) encryption standards. If used with a 802.1X server or in pre-shared key mode with a strong and uncommon passphrase WPA2 is still considered secure by many IT professionals.[by whom?]
[edit] PiggybackingMain article: Piggybacking (Internet access)
Piggybacking refers to access to a wireless Internet connection by bringing one's own computer within the range of another's wireless connection, and using that service without the subscriber's explicit permission or knowledge.
During the early popular adoption of 802.11, providing open access points for anyone within range to use was encouraged[by whom?] to cultivate wireless community networks,[44] particularly since people on average use only a fraction of their downstream bandwidth at any given time.
Recreational logging and mapping of other people's access points has become known as wardriving. Indeed, many access points are intentionally installed without security turned on so that they can be used as a free service. Providing access to one's Internet connection in this fashion may breach the Terms of Service or contract with the ISP. These activities do not result in sanctions in most jurisdictions; however, legislation and case law differ considerably across the world. A proposal to leave graffiti describing available services was called warchalking.[45] A Florida court case determined that owner laziness was not to be a valid excuse.[46]
Piggybacking often occurs unintentionally, most access points are configured without encryption by default, and operating systems can be configured to connect automatically to any available wireless network. A user who happens to start up a laptop in the vicinity of an access point may find the computer has joined the network without any visible indication. Moreover, a user intending to join one network may instead end up on another one if the latter has a stronger signal. In combination with automatic discovery of other network resources (see DHCP and Zeroconf) this could possibly lead wireless users to send sensitive data to the wrong middle-man when seeking a destination (see Man-in-the-middle attack). For example, a user could inadvertently use an insecure network to log in to a website, thereby making the login credentials available to anyone listening, if the website uses an insecure protocol such as HTTP.

Wednesday 9 March 2011

===Operational advantages===

Operational advantages
Wi-Fi allows the deployment of [[local area network]]s (LANs) without wires for client devices, typically reducing the costs of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs.
{{As of| 2010}} manufacturers are building wireless network adapters into most laptops. The price of [[chipset]]s for Wi-Fi continues to drop, making it an economical networking option included in even more devices. Wi-Fi has become widespread in corporate infrastructures.{{Citation needed|date=March 2010}}
Different competitive brands of access points and client network-interfaces can inter-operate at a basic level of service. Products designated as "Wi-Fi Certified" by the Wi-Fi Alliance are backwards compatible. "Wi-Fi" designates a globally operative set of standards: unlike [[mobile phone]]s, any standard Wi-Fi device will work anywhere in the world.
Wi-Fi operates in more than 220,000 public hotspots and in tens of millions of homes and corporate and university campuses worldwide.<ref>{{Cite web|title=Wi-Fi Finder|url=http://www.jiwire.com/search-hotspot-locations.htm|publisher=jiwire.com|accessdate=2008-04-20}}</ref>
The current version of [[Wi-Fi Protected Access]] encryption (WPA2) {{As of| 2010 | lc = on}} is considered{{By whom|date=March 2010}} secure, provided users employ a strong [[passphrase]].  New protocols for [[quality of service|quality-of-service]] ([[Wireless Multimedia Extensions|WMM]]) make Wi-Fi more suitable for latency-sensitive applications (such as voice and video); and power saving mechanisms (WMM Power Save) improve battery operation.

Limitations

limitationsSpectrum assignments and operational limitations are not consistent worldwide: most of Europe allows for an additional two channels beyond those permitted in the U.S. for the 2.4 GHz band (1–13 vs. 1–11), while Japan has one more on top of that (1–14). Europe, as of 2007[update], was essentially homogeneous in this respect. Note that: Wi-Fi cannot be used in Italy without a licence, and in both Italy and France, both ends of the Wi-Fi link must be within the same building (i.e. a Wi-Fi active device cannot be used out of doors).
A Wi-Fi signal occupies five channels in the 2.4 GHz band; any two channels whose channel numbers differ by five or more, such as 2 and 7, do not overlap. The oft-repeated adage that channels 1, 6, and 11 are the only non-overlapping channels is, therefore, not accurate; channels 1, 6, and 11 do, however, comprise the only group of three non-overlapping channels in the U.S.
Equivalent isotropically radiated power (EIRP) in the EU is limited to 20 dBm (100 mW).
The current 'fastest' norm 802.11n uses double the radio spectrum compared to 802.11a or 802.11g. This means there can only be one 802.11n network on 2.4 GHz band without interference to other WLAN traffic, or none, if there already is an AP on any of the mid channels.
The on-coming 802.11ac will jam all the current WLAN bands, if allowed on same bands. There might be a chance the 802.11ac would be allocated a new band, perhaps on UHF TV white space.
The Internet protocol performs poorly in the face of noise when run with WiFi as the physical layer.[citation needed] TCP has been tuned for a wired network in which packets lost due to noise is very rare and packets are lost almost exclusively due to congestion. On a wireless network, noise is common. This difference causes TCP to greatly slow or break transmission when noise is significant, even when most packets are still arriving correctly.
 ReachSee also: Long-range Wi-Fi
Wi-Fi networks have limited range. A typical wireless router using 802.11b or 802.11g with a stock antenna might have a range of 32 m (120 ft) indoors and 95 m (300 ft) outdoors. The IEEE 802.11n however, can exceed that range by more than two times.[30] Range also varies with frequency band. Wi-Fi in the 2.4 GHz frequency block has slightly better range than Wi-Fi in the 5 GHz frequency block. Outdoor ranges - through use of directional antennas - can be improved with antennas located several kilometres or more from their base. In general, the maximum amount of power that a Wi-Fi device can transmit is limited by local regulations, such as FCC Part 15[31] in USA.
Due to reach requirements for wireless LAN applications, Wi-Fi has fairly high power consumption compared to some other standards. Technologies such as Bluetooth (designed to support wireless PAN applications) provide a much shorter propagation range of <10m[32] and so in general have a lower power consumption. Other low-power technologies such as ZigBee have fairly long range, but much lower data rate. The high power consumption of Wi-Fi makes battery life in mobile devices a concern.
Researchers have developed a number of "no new wires" technologies to provide alternatives to Wi-Fi for applications in which Wi-Fi's indoor range is not adequate and where installing new wires (such as CAT-5) is not possible or cost-effective. For example, the ITU-T G.hn standard for high speed Local area networks uses existing home wiring (coaxial cables, phone lines and power lines). Although G.hn does not provide some of the advantages of Wi-Fi (such as mobility or outdoor use), it's designed for applications (such as IPTV distribution) where indoor range is more important than mobility.
Due to the complex nature of radio propagation at typical Wi-Fi frequencies, particularly the effects of signal reflection off trees and buildings, algorithms can only approximately predict Wi-Fi signal strength for any given area in relation to a transmitter.[33] This effect does not apply equally to long-range Wi-Fi, since longer links typically operate from towers that broadcast above the surrounding foliage.
MobilitySpeed vs. Mobility of wireless systems: Wi-Fi, HSPA, UMTS, GSMThe very limited practical range of Wi-Fi essentially confines mobile use to such applications as inventory-taking machines in warehouses or in retail spaces, barcode-reading devices at check-out stands, or receiving/shipping stations. Mobile use of Wi-Fi over wider ranges is limited, for instance, to uses such as in an automobile moving from one hotspot to another (known as Wardriving). Other wireless technologies are more suitable as illustrated in the graphic.
 Data security risks
The most common wireless encryption-standard, Wired Equivalent Privacy (WEP), has been shown to be easily breakable even when correctly configured. Wi-Fi Protected Access (WPA and WPA2) encryption, which became available in devices in 2003, aimed to solve this problem. Wi-Fi access points typically default to an encryption-free (open) mode. Novice users benefit from a zero-configuration device that works out-of-the-box, but this default does not enable any wireless security, providing open wireless access to a LAN. To turn security on requires the user to configure the device, usually via a software graphical user interface (GUI). On unencrypted Wi-Fi networks connecting devices can monitor and record data (including personal information), but such networks may use other means of protection, such as a VPN or secure Hypertext Transfer Protocol (HTTPS) over Transport Layer Security.
 PopulationMany 2.4 GHz 802.11b and 802.11g access-points default to the same channel on initial startup, contributing to congestion on certain channels. To change the channel of operation for an access point requires the user to configure the device. Yet, regular users selecting a "free" channel usually leads to even worse congestion, due to the overlapping channel system. Observations during the year 2010 have shown pretty acceptable spreading of by far most of the devices being on one of the "good" channels: 1, 6 or 11.[citation needed]
 Channel pollutionFor more details on this topic, see Electromagnetic interference at 2.4 GHz.
Market forces may drive a process of standardization. Interoperability issues between non-Wi-Fi brands or proprietary deviations from the standard can still disrupt connections or lower throughput speeds on all devices within range, including any non-Wi-Fi or proprietary product. Moreover, the usage of the ISM band in the 2.45 GHz range is also common to Bluetooth, WPAN-CSS, ZigBee, and any new system will take its share.
Wi-Fi pollution, or an excessive number of access points in the area, especially on the neighboring channel, can prevent access and interfere with other devices' use of other access points, caused by overlapping channels in the 802.11g/b spectrum, as well as with decreased signal-to-noise ratio (SNR) between access points. This can become a problem in high-density areas, such as large apartment complexes or office buildings with many Wi-Fi access points. Additionally, other devices use the 2.4 GHz band: microwave ovens, security cameras, ZigBee devices, Bluetooth devices and (in some countries) Amateur radio, video senders, cordless phones and baby monitors, all of which can cause significant additional interference. It is also an issue when municipalities[34] or other large entities (such as universities) seek to provide large area coverage.


Internet access

Internet access
A roof-mounted Wi-Fi antennaA Wi-Fi enabled device such as a personal computer, video game console, smartphone or digital audio player can connect to the Internet when within range of a wireless network connected to the Internet. The coverage of one or more (interconnected) access points — called hotspots — can comprise an area as small as a few rooms or as large as many square miles. Coverage in the larger area may depend on a group of access points with overlapping coverage. Wi-Fi technology has been used in wireless mesh networks, for example, in London, UK.[15]
In addition to private use in homes and offices, Wi-Fi can provide public access at Wi-Fi hotspots provided either free-of-charge or to subscribers to various commercial services. Organizations and businesses - such as those running airports, hotels and restaurants - often provide free-use hotspots to attract or assist clients. Enthusiasts or authorities who wish to provide services or even to promote business in selected areas sometimes provide free Wi-Fi access. As of 2008[update] more than 300 metropolitan-wide Wi-Fi (Muni-Fi) projects had started.[16] As of 2010[update] the Czech Republic had 1150 Wi-Fi based wireless Internet service providers.[17][18]
Routers that incorporate a digital subscriber line modem or a cable modem and a Wi-Fi access point, often set up in homes and other premises, can provide Internet access and internetworking to all devices connected (wirelessly or by cable) to them. With the emergence of MiFi and WiBro (a portable Wi-Fi router) people can easily create their own Wi-Fi hotspots that connect to Internet via cellular networks. Now iPhone, Android or Symbian phones can create wireless connections.[19]
One can also connect Wi-Fi devices in ad-hoc mode for client-to-client connections without a router. Wi-Fi also connects places that would traditionally not have network access, for example kitchens and garden sheds.
[edit] City-wide Wi-FiFurther information: Municipal wireless network

An outdoor Wi-Fi access point in Minneapolis
An outdoor Wi-Fi access point in TorontoIn the early 2000s, many cities around the world announced plans for city-wide Wi-Fi networks. This proved to be much more difficult than their promoters initially envisioned with the result that most of these projects were either canceled or placed on indefinite hold. A few were successful, for example in 2005, Sunnyvale, California became the first city in the United States to offer city-wide free Wi-Fi,[20] and Minneapolis has generated $1.2 million profit annually for their provider.[21]
In May, 2010, London, UK Mayor Boris Johnson pledged London-wide Wi-Fi by 2012.[22] Both the City of London, UK[23] and Islington[24] already have extensive outdoor Wi-Fi coverage.
[edit] Campus-wide Wi-FiCarnegie Mellon University built the first wireless Internet network in the world at their Pittsburgh campus in 1994,[25] long before Wi-Fi branding originated in 1999. Many traditional college campuses provide at least partial wireless Wi-Fi Internet coverage.
Drexel University in Philadelphia made history by becoming the United States' first major university to offer completely wireless Internet access across the entire campus in 2000.[26]
[edit] Direct computer-to-computer communicationsWi-Fi also allows communications directly from one computer to another without the involvement of an access point. This is called the ad hoc mode of Wi-Fi transmission. This wireless ad hoc network mode has proven popular with multiplayer handheld game consoles, such as the Nintendo DS, digital cameras, and other consumer electronics devices.
Similarly, the Wi-Fi Alliance promotes a specification called Wi-Fi Direct for file transfers and media sharing through a new discovery- and security-methodology.[27] Wi-Fi Direct launched in October 2010.[28]
[edit] Future directionsAs of 2010[update] Wi-Fi technology has spread widely within business and industrial sites. In business environments, just like other environments, increasing the number of Wi-Fi access points provides network redundancy, support for fast roaming and increased overall network-capacity by using more channels or by defining smaller cells. Wi-Fi enables wireless voice-applications (VoWLAN or WVOIP). Over the years, Wi-Fi implementations have moved toward "thin" access points, with more of the network intelligence housed in a centralized network appliance, relegating individual access points to the role of "dumb" transceivers. Outdoor applications may utilize mesh topologies.