All TCP/IP permitted equipment attached to the Web have an Web Method (IP) deal with. Just like an unknown variety, it will help to slightly recognize a customer of the system. The Web Given Statistics Specialist (IANA) is the company liable for determining IP covers to Web Service Services (ISPs) and determining which ones should be used for the public Web and which ones should be used on confidential systems.
IP covers are in fact a sequence of 32 binary numbers or pieces. For convenience of use, system designers often split these 32 pieces into four pieces of 8 pieces (or octets), each addressing a variety from 0 to 255. Each variety is then divided by a period (.) to make the well known filled decimal note. An example of an IP deal with that follows these regulations is 18.104.22.168.
Private IP Addresses
Some groups of IP addresses are reserved for use only in private networks and are not routed over the Internet. These are called private IP addresses and have the following ranges:
10.0.0.0 - 10.255.255.255 172.16.0.0 - 172.31.255.255 192.168.0.0 - 192.168.255.255
Home networking equipment/devices usually are configured in the factory with an IP address in the range 192.168.1.1 to 192.168.1.255.
You may be wondering how devices using private addresses could ever access the Internet if the use of private addresses on the Internet is illegal. The situation gets even more confusing if you consider the fact that hundreds of thousands of office and home networks use these same addresses. This must cause networking confusion. Don’t worry, this problem is overcome by NAT.
The localhost IP Address
Whether or not your computer has a network interface card it will have a built-in IP address with which network-aware applications can communicate with one another. This IP address is defined as 127.0.0.1 and is frequently referred to as localhost. This concept is important to understand, and will be revisited in many later chapters.
Network Address Translation (NAT) Makes Private IPs Public
Your router/firewall will frequently be configured to give the impression to other devices on the Internet that all the servers on your home/office network have a valid public IP address, and not a “private” IP address. This is called network address translation (NAT) and is often also called IP masquerading in the Linux world. There are many good reasons for this, the two most commonly stated are:
You can configure NAT to be one to one in which you request your ISP to assign you a number of public IP addresses to be used by the Internet-facing interface of your firewall and then you pair each of these addresses to a corresponding server on your protected private IP network. You can also use many to one NAT, in which the firewall maps a single IP address to multiple servers on the network.
As a general rule, you won’t be able to access the public NAT IP addresses from servers on your home network. Basic NAT testing requires you to ask a friend to try to connect to your home network from the Internet.
Port Forwarding with NAT Facilitates Home-Based Web sites
In a simple home network, all servers accessing the Internet will appear to have the single public IP address of the router/firewall because of many to one NAT. Because the router/firewall is located at the border crossing to the Internet, it can easily keep track of all the various outbound connections to the Internet by monitoring:
This arrangement works well with a single NAT IP trying to initiate connections to many Internet addresses. The reverse isn’t true.
New connections initiated from the Internet to the public IP address of the router/firewall face a problem. The router/firewall has no way of telling which of the many home PCs behind it should receive the relayed data because the mapping mentioned earlier doesn’t exist beforehand. In this case the data is usually discarded.
Port forwarding is a method of counteracting this. For example, you can configure your router/firewall to forward TCP port 80 (Web/HTTP) traffic destined to the outside NAT IP to be automatically relayed to a specific server on the inside home network
As you may have guessed, port forwarding is one of the most common methods used to host Web sites at home with DHCP DSL.
The Dynamic Host Configuration Protocol (DHCP) is a protocol that automates the assignment of IP addresses, subnet masks default routers, and other IP parameters.
The assignment usually occurs when the DHCP configured machine boots up, or regains connectivity to the network. The DHCP client sends out a query requesting a response from a DHCP server on the locally attached network. The DHCP server then replies to the client PC with its assigned IP address, subnet mask, DNS server and default gateway information.
The assignment of the IP address usually expires after a predetermined period of time, at which point the DHCP client and server renegotiate a new IP address from the server’s predefined pool of addresses. Configuring firewall rules to accommodate access from machines who receive their IP addresses via DHCP is therefore more difficult because the remote IP address will vary from time to time. You’ll probably have to allow access for the entire remote DHCP subnet for a particular TCP/UDP port.
Most home router/firewalls are configured in the factory to be DHCP servers for your home network. You can also make your Linux box into a DHCP server, once it has a fixed IP address.
The most commonly used form of DSL will also assign the outside interface of your router/firewall with a single DHCP provided IP address.
How DNS Links Your IP Address To Your Web Domain
The domain name system (DNS) is a worldwide server network used to help translate easy to remember domain names like www.linuxhomenetworking.com into an IP address that can be used behind the scenes by your computer. Here step by step description of what happens with a DNS lookup.
As you can imagine, this process can cause a noticeable delay when you are browsing the Web. Each server in the chain will store the most frequent DNS name to IP address lookups in a memory cache which helps to speed up the response.
IP Version 6 (IPv6)
Most Internet-capable networking devices use version 4 of the Internet Protocol (IPv4) which I have described here. You should also be aware that there is now a version 6 (IPv6) that has recently been developed as a replacement.
With only 32 bits, the allocation of version 4 addresses will soon be exhausted between all the world’s ISPs. Version 6, which uses a much larger 128-bit address offers eighty billion, billion, billion times more IP addresses which it is hoped should last for most of the 21st century.
IPv6 packets are also labeled to provide quality-of-service information that can be used in prioritizing real-time applications, such as video and voice, over less time-sensitive ones such as regular Web surfing and chat. IPv6 also inherently supports the IPSec protocol suite used in many forms of secured networks, such as virtual private networks (VPNs).
Most current operating systems support IPv6 even though it isn’t currently being used extensively within corporate or home environments. Expect it to become an increasingly bigger part of your network planning in years to come.
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