Monday, 4 February 2013

Internet Protocol Summary - Facts about IP



Name:

Internet Protocol - abbreviated "IP"

Description:

IP is used by many higher level network protocols, principally TCP and UDP. Many Internet software applications including Web browsers, FTP clients, and email programs, rely on Internet Protocol.

OSI Model:

Network layer (Layer 3)

Datagram Format:

A base header 20 bytes (5 "longwords") in length, with the option for expanded header options, followed by data.

Header:



Word 1 -
  • Version - 4 bits
  • Header Length (in longwords) - 4 bits
  • Type of Service / Differentiated Services Code Point (DSCP) - 8 bits
  • Datagram Length (in bytes) - 16 bits
Word 2 -
  • ID Number - 16 bits
  • Fragmentation Flags - 3 bits
  • Fragmentation Offset - 13 bits
Word 3 -
  • Time to Live - 8 bits
  • Transport Protocol - 8 bits
  • Header Checksum - 16 bits
Word 4 -
  • Source IP Address - 32 bits
Word 5 -
  • Destination IP Address - 32 bits
Variable length fields -
  • Options
  • Padding

Payload:

IP datagram payloads can be of variable length. The minimum size of an IP datagram is 28 bytes, using the minimum 20 bytes of header information, followed by the minimum of 8 bytes of data. The maximum size of an IP datagram payload is 65,535 bytes minus the header size.

Footer:

Internet Protocol does not use its own datagram footer.

Internet Protocol Tutorial



Classes of IP Addresses, IP Broadcast and IP Multicast



IPv4 Address Classes

The IPv4 address space can be subdivided into 5 classes - Class A, B, C, D and E. Each class consists of a contiguous subset of the overall IPv4 address range.

With a few special exceptions explained further below, the values of the leftmost four bits of an IPv4 address determine its class as follows:

Class
Leftmost bits
Start address
Finish address
A
0xxx
0.0.0.0
127.255.255.255
B
10xx
128.0.0.0
191.255.255.255
C
110x
192.0.0.0
223.255.255.255
D
1110
224.0.0.0
239.255.255.255
E
1111
240.0.0.0
255.255.255.255






All Class C addresses, for example, have the leftmost three bits set to '110', but each of the remaining 29 bits may be set to either '0' or '1' independently (as represented by an x in these bit positions):
110xxxxx xxxxxxxx xxxxxxxx xxxxxxxx
Converting the above to dotted decimal notation, it follows that all Class C addresses fall in the range from 192.0.0.0 through 223.255.255.255.

IP Address Class E and Limited Broadcast

The IPv4 networking standard defines Class E addresses as reserved, meaning that they should not be used on IP networks. Some research organizations use Class E addresses for experimental purposes. However, nodes that try to use these addresses on the Internet will be unable to communicate properly.
A special type of IP address is the limited broadcast address 255.255.255.255. A broadcast involves delivering a message from one sender to many recipients. Senders direct an IP broadcast to 255.255.255.255 to indicate all other nodes on the local network (LAN) should pick up that message. This broadcast is 'limited' in that it does not reach every node on the Internet, only nodes on the LAN.
Technically, IP reserves the entire range of addresses from 255.0.0.0 through 255.255.255.255 for broadcast, and this range should not be considered part of the normal Class E range.

IP Address Class D and Multicast

The IPv4 networking standard defines Class D addresses as reserved for multicast. Multicast is a mechanism for defining groups of nodes and sending IP messages to that group rather than to every node on the LAN (broadcast) or just one other node (unicast).
Multicast is mainly used on research networks. As with Class E, Class D addresses should not be used by ordinary nodes on the Internet.

IP Address Class A, Class B, and Class C

Class A, Class B, and Class C are the three classes of addresses used on IP networks in common practice, with three exceptions as explained next.

IP Loopback Address

127.0.0.1 is the loopback address in IP. Loopback is a test mechanism of network adapters. Messages sent to 127.0.0.1 do not get delivered to the network. Instead, the adapter intercepts all loopback messages and returns them to the sending application. IP applications often use this feature to test the behavior of their network interface.

http://z.about.com
As with broadcast, IP officially reserves the entire range from 127.0.0.0 through 127.255.255.255 for loopback purposes. Nodes should not use this range on the Internet, and it should not be considered part of the normal Class A range.

Zero Addresses

As with the loopback range, the address range from 0.0.0.0 through 0.255.255.255 should not be considered part of the normal Class A range. 0.x.x.x addresses serve no particular function in IP, but nodes attempting to use them will be unable to communicate properly on the Internet.

Private Addresses

The IP standard defines specific address ranges within Class A, Class B, and Class C reserved for use by private networks (intranets). The table below lists these reserved ranges of the IP address space.
IP Testing as per IEC 60529, An ISO 17025 (NABL) Accredited Lab
Class
Private start address
Private finish address
A
10.0.0.0
10.255.255.255
B
172.16.0.0
172.31.255.255
C
192.168.0.0
192.168.255.255
Nodes are effectively free to use addresses in the private ranges if they are not connected to the Internet, or if they reside behind firewalls or other gateways that use Network Address Translation (NAT).

IPv6 Address Types

IPv6 does not use classes. IPv6 supports the following three IP address types:
  • unicast
  • multicast
  • anycast
Unicast and multicast messaging in IPv6 are conceptually the same as in IPv4. IPv6 does not support broadcast, but its multicast mechanism accomplishes essentially the same effect. Multicast addresses in IPv6 start with 'FF' (255) just like IPv4 addresses.
Anycast in IPv6 is a variation on multicast. Whereas multicast delivers messages to all nodes in the multicast group, anycast delivers messages to any one node in the multicast group. Anycast is an advanced networking concept designed to support the failover and load balancing needs of applications.

IPv6 Reserved Addresses

IPv6 reserves just two special addresses: 0:0:0:0:0:0:0:0 and 0:0:0:0:0:0:0:1. IPv6 uses 0:0:0:0:0:0:0:0 internal to the protocol implementation, so nodes cannot use it for their own communication purposes. IPv6 uses 0:0:0:0:0:0:0:1 as its loopback address, equivalent to 127.0.0.1 in IPv4.


Sunday, 3 February 2013

How to Connect to a Wireless Network in Windows 7




With every iteration of Windows, Microsoft improves the ease in which we connect to wireless networks. However there are still some of us that are baffled by the steps necessary to connect to wireless networks and the configuration steps necessary.That's why in this guide I will show you step-by-step how to connect to a wireless network using Windows 7.

Wireless Networks Surround Us

One of the first things that you will notice when you follow the steps in this guide is that there are a lot of wireless networks out there, however this doesn't mean you should connect to them because you could be compromising your computer's security.

Public Wireless Networks Are Unsafe

The biggest problem encountered by users that connect to public unencrypted networks is that someone can hijack your connection and see what you are transferring over the airwaves.
To put it simply - if a network is public and does not have encryption, avoid it. Now that you've been warned about the dangers of connecting to public networks, I can show you how to connect to wireless networks using Windows 7.

View Available Wireless Networks & Connect

1. To view a list of available wireless networks click the Wireless Networking icon in the Notification area on the left side of the Taskbar.
Note: If the network you are trying to connect to is not listed, the router may not be broadcasting the network's SSID (wireless network's name). If this is the case refer to your router's documentation to determine the steps necessary to enabled SSID broadcasting.
A Word About Signal Strength
You will also notice that each wireless network has a signal strength indicator that provides a visual guide to determine the strength of the wireless signal. All green bars means Excellent signal, one bar equals poor signal.
2. Once you identify the network you wish to connect to from the list, click on the network name and then click Connect.
Note: Before you connect to the network you will have an opportunity to check Connect Automatically so that your computer will automatically connect to the network when in range.
If the network you are trying to connect to is unsecured, meaning that a password is not required to connect to the network, you should be able to access the internet and other network resources right away. However, if the network is secured you will need to follow the step below to connect.
Secured Networks Require Authentication

If you are connecting to a secured wireless network you will have two options to authenticate. You can enter the required password or if your router supports it you can use the Secure Easy Setup button on the router.

Option 1 - Enter Password

1. When prompted enter the password for the router you are connecting to. To view the characters in the text field uncheck Hide characters.

This is especially useful if the password is long and complex.

Note: As soon as you enter a character in the password field you will not be able to use Secure Easy Setup to connect to the router.

2. Click OK to connect.

Option 2 - Secure Easy Setup

1. When prompted to enter the password, walk over to the router and press the Secure Easy Setup button on the router. After a couple of seconds the computer should connect to the wireless network.

Note: If Secure Easy Setup does not work, try again. If it is still not working it may be disabled on your router. Consult the router's instruction manual in order to enable and configure the feature.

You should now be connected to the wireless network. Learn more about sharing files and managing wireless network profiles.