TCP/IP First-Step [Electronic resources] نسخه متنی

What does an IP packet do?

Answer: An IP packet wraps a user's application data into a neat package that protects and conveys that data through a network. This packet bears the user's "return address" (an IP address), the intended recipient's IP address, and other useful information as the packet gets pushed through a network to the destination machine.

How many stages are there in the life of an IP packet?

Answer: Exactly three: The first stage is when the packet is created. Part of this creation process is adding all the necessary information to the packet's header to support bidirectional communications with the destination machine.

The second stage occurs when that packet gets wrapped in the transport mechanism (known as a frame) of the physical network carrying the IP packet.

The third and final stage occurs when the packet reaches its destination. At that point, the recipient checks the information contained in the IP header to ensure that the data is error free, and then strips the data out of the packet. At that point, the packet's mission has been accomplished and it is discarded.

Can an IP packet roam the network forever in search of its destination?

Answer: No! IP packets have a pre-set Time-To-Live (TTL), and when that expires the packet is destroyed. Thus, an IP packet must reach its destination before it gets too old. Old is a relative term; for an IP address it is defined in terms of the number of network devices it can pass through rather than some arbitrary amount of time.

What is an IP address?

Answer: An IP address is a 32-bit binary number that uniquely identifies both an IP-enabled machine and the network to which it is connected.

Why do you need IP addresses?

Answer: Without an IP address, no machine could be uniquely identified in an IP network. Without a reliable means of identifying machines, you can't support communications between two or more machines.

Do you need those dots between the numbers in an IP address?

Answer: No, not really. The periods are there to make things easier for human beings. In its native form, an IP address is just a string of 32 binary digits, each of which can have a value of either 0 or 1.

Long strings of binary numbers are beyond the ability of people, so two things make IP addresses usable. The first is to chop it into 4 groups of 8 bits each. These groups are separated visually with the dots. Then, the string of binary digits represented by each group of 8 bits is converted to a decimal number. This allows you to work with relatively small decimal numbers rather than with lengthy binary numbers.

How do people use IP addresses?

Answer: IP addresses can be used directly by people to access anything connected to the Internet or any other IP network. Unfortunately, IP addresses tend to be difficult to remember. Thus, they tend to get used indirectly; people use friendly words such as www.cisco.com to access network-attached resources. These friendly words are translated to IP addresses behind the scenes.

Network administrators also use IP addresses as a way of organizing the resources connected to the networks they are responsible for managing. That organization is possible thanks to the two-part hierarchical structure of each IP address.

How does a network use IP addresses?

Answer: Routers, the communications devices that make up an IP network, use IP addresses as the basis for communicating known destinations and possible paths with each other. This behind-the-scenes process assures you that the network is constantly looking for the best paths between your network and any and all possible destination network addresses. Routers also must find each packet's destination IP address so they can forward the packets appropriately.

What's the difference between a host address and a network address?

Answer: An IP address has two parts: a host address and a network address. All the machines connected to one network share that network's address. In fact, that network address forms the beginning of the host addresses. Each host, however, must have a unique address. The host address portion of each IP address is where the IP addresses must differ.