The Internet is a vast source of information that is continuously updated and accessed via computers and other devices. For a device (also referred to as a host) to connect to the Internet, it is necessary that among other configurations, it must have an Internet Protocol (IP) address. The IP address is the computer's address on the Internet. A common comparison of an IP address is an individual's telephone number, which is an identifier for people to communicate with the individual. Up until the late 1980s, configuring a computer to connect to the Internet was a manual process. The protocol Bootstrap Protocol (BOOTP) was the first Transmission Control Protocol/Internet Protocol (TCP/IP) network configuration tool used to prevent the task of having to manually assign IP addresses by automating the process.
While the introduction of the BOOTP network protocol was a welcome innovation for network administrators tasked with managing large numbers of computers on a network, it was the first attempt and a new and improved TCP/IP network protocol soon followed. This protocol is called Dynamic Host Configuration Protocol (DHCP). DHCP was not designed as a replacement for BOOTP, but an extension of its functionality.
How DHCP WorksAs its name indicates, DHCP provides dynamic IP address assignment. What this means is that instead of having to rely on a specific IP address, a computer will be assigned one that is available from a subnet or "pool" that is assigned to the network. DHCP also extends BOOTP functionality to provide IP addresses that expire. BOOTP indirectly uses a form of leasing that never expired, but the term wasn't actually used until the introduction of DHCP. When DHCP assigns an IP address, it actually leases the identifier to the host computer for a specific amount of time. The default lease is five days, but a network administrator should evaluate their own particular circumstances to determine an appropriate lease.
In basic terms, the DHCP lease process works as follows:
A network device attempts to connect to the Internet.
The network requests an IP address.
The DHCP server allocates (leases) the network device an IP address, which is forwarded to the network by a router.
DHCP updates the appropriate network servers with the IP address and other configuration information.
The network device accepts the IP address.
The IP address lease expires.
DHCP either reallocates the IP address or leases one that is available.
The network device is no longer connected to the Internet.
The IP address becomes an available address in the network pool of IP addresses.
To set up DHCP, you basically need a DHCP-supported client (at least one) and router, and a DHCP server. The client is a computer or other device on a network that requires an IP address and or other network configuration information. The router functions as a forwarding (or routing) agent of IP address requests from the DHCP server. The DHCP server is key to the entire operation. It is responsible for allocating, leasing, reallocating, and renewing IP addresses. Windows and Linux both support DHCP software.
Thursday, April 29, 2010
What is DHCP? How does it work?
Dynamic vs Static IP Addresses
Static IP addressing is for one customer on one IP address and Dynamic IP addressing assigns a different IP address each time the ISP customer logs on to their computer, but this is dependent upon the Internet Service Provider (ISP) because some ISP's only change the IP address as they deem it necessary.
If you have Dynamic IP Addressing through your Website Host it means that you are sharing an IP Address with several other customers.
If you are a beginner on the internet, an avid internet user, are entertaining the thought of starting your own website business, are a gamer, use VOIP or VPN there are several things you should know about IP Addressing.
Static IP Addressing:
If you feel the need to always know what your IP address is then you need a Static IP address, because it is constant. Static IP addresses are more reliable for Voice over Internet Protocol (VOIP), more reliable to host a gaming website or to play X-Box, Play Station, use Virtual Private Network for secure access to files from your company network computer, etc. Static IP addresses are also great if you use your computer as a server, as it should give your file server faster file uploads and downloads. Another plus with Static IP's, when hosting a website you are not sharing your IP with another company who sends out a lot of E-mail SPAM and not only has their website been shut down but in turn gets your IP address blacklisted.
In contrast a static IP address can become a security risk, because the address is always the same. Static IP's are easier to track for data mining companies. Static IP addressing is less cost effective than Dynamic IP Addressing.
Dynamic IP Addressing:
The biggest advantages of Dynamic IP Addressing are less security risk as the computer is assigned a new IP address each time the customer logs on, they are cost effective and there is automatic network configuration (the less human intervention with network configuration the better). Dynamic addressing is usually used by ISP's so that one IP address can be assigned to several users, however some ISP's use Sticky Dynamic IP Addressing and do not change the IP address very often. Dynamic IP Addressing can be used by families with several computers or by a small business owner who has a home office. The software that comes with a router allows for Dynamic Host Configuration Protocol (DHCP) setup and assigns each computer attached to the router an IP address automatically.
In contrast, Dynamic IP addressing should not be used for VOIP, VPN, playing online games or game hosting because Dynamic IP addressing is less reliable then Static IP addressing and could cause the service to disconnect while you are on a VOIP, VPN or gaming.
What is a Hostname?
A name is a label that is used to distinguish one thing from another. A person's name, for instance, comprises a set of alphabetic characters that allows a person to be individually addressed. Computers are also named to differentiate one machine from another and to allow for such activities as network communication.
Computers have always needed unique addresses to talk to each other. With the advent of the Internet, the requirements for enabling computers to communicate with each other on a network included the concept of the hostname. The hostname began as a simple string of alphanumeric characters (and possibly a hyphen) and has evolved to its current definition, where hostname means a Fully Qualified Domain Name (FQDN) that absolutely and uniquely identifies every computer hooked up to the Internet via the Domain Name Service (DNS) naming hierarchy.
The true "name" a computer needs in order to communicate on a network is actually a set of numbers. The original computers connected as the Internet used small integers as the host number. For TCP/IP, the main protocol used by the Internet, each computer has a network IP address that follows a specific set of rules to assure its uniqueness and validity. (Additionally, port numbers further specify the access points for particular services on a computer).
It has always been user friendly to associate a host name with a computer (while the computer maintained its internal numerical host number or network address). One of the initial Internet RFCs, "Standardization of Host Mnemonics" lists the table that associated host numbers with their corresponding host names for the first Internet computers. This table was kept in a file called HOST.TXT that was stored on every computer that wished to communicate.
While the original file was not so daunting at 20 entries, it became quickly apparent that this solution was not scalable or flexible enough as the number of host computers connected to the Internet exploded. In order to accommodate the problem of connecting all of the new computers being added to the Internet, a hierarchical database of host names was created called DNS. DNS associates host names with their IP addresses. A complete domain name (that is, an FQDN) includes the name of the host concatenated with its domain name. This naming convention allows for a hierarchy of domain names with the host name being the most specific (and "left-most") part.
The rules for a host name were first standardized in the original host name specification, "DoD Internet Host Table Specification". It states that the name should be a text string consisting of the letters A through Z (upper or lower case), digits 0 through 9, the minus sign (-), and the period (.). Note, the period is only allowed as the last character of the host name if it is the delimiter of the full domain name (FQDN). No spaces are permitted as part of a name. The first character must be an alphabetic character and the last character must not be a minus sign or period. It was also recommended that the host name be no longer than 24 characters in length. Subsequently, in "Requirements for Internet Hosts - Application and Support", the host name rules were updated. The first character could now be either a letter or a digit and software dealing with host names must handle names up to 63 characters in length.
In common usage today, hostname refers specifically to the FQDN that comprises the name of the host, a period, and the domain name. The domain name is composed of labels that begin with the top-level domain and are arranged right to left for the second and, possibly, third level labels. The host name and the domain labels are separated by periods. The total length of the hostname as an FQDN cannot exceed 255 character with each domain name label having a maximum length of 63 characters. For example, if a company's domain name is "example.com." and a particular computer in the company has been named "plato", the hostname for that computer will be "plato.example.com.". Note, that technically FQDNs end in a period to unambiguously define the hostname and to be sure that it is not part of a longer domain name. (although in common usage this final period is often omitted).
The exact rules for the new hostname definition that has evolved is also more rigorous than that of the related original host name specification. The DNS naming rules are explained in "Domain Names - Concepts and Facilities", "Domain Names - Implementation and Specification", and "Clarifications to the DNS Specification".
To summarize, a hostname is a Fully Qualified Domain Name that uniquely and absolutely names a computer. It is composed of the host name and the domain name. The domain name in turn is one or more domain labels that place the computer in the DNS naming hierarchy. The host name and the domain name labels are separated by periods and the total length of the hostname cannot exceed 255 characters.
Now that the syntax of the name of the host as part of the hostname is understood, how does one choose a good name for their computer? Several web sites offer suggestions and the choice is up to the system administrator whose whimsy is only limited to the fact that no two computers in one domain space can have the same host name (because the two computers would have the same hostname!).
RFC 1178, "Choosing a Name for Your Computer" contains several guidelines on how to name - and how not to name - your computers.
A summary of sample guidelines for good host names:
Use words/names that are rarely used.
Use theme names.
Use real words.
Don't worry about reusing someone else's hostname.
There is always room for an exception.
And some sample guidelines for not so good host names:
Don't overload other terms already in common use.
Don't choose a name after a project unique to that machine.
Don't use your own name.
Don't use long names.
Avoid alternate spellings.
Avoid domain names.
Avoid domain-like names.
Don't use antagonistic or otherwise embarrassing names.
Don't use digits at the beginning of the name.
Don't use non-alphanumeric characters in a name.
Don't expect case to be preserved
As a final note, the terms "host name" and "hostname" are often used interchangeably, so be sure to clarify when the term is being used as to whether just the name of the host or the computer's FQDN is being referenced. To see this on a Linux system, by example, the hostname command returns the FQDN while adding the -s option (i.e., hostname -s) returns just the name of the host.
What is my hostname?
Reverse DNS turns an IP address into a hostname -- for example, it might turn 192.0.2.25 into host.example.com. Reverse DNS (rDNS) is a method of resolving an IP address into a domain name, just as the domain name system (DNS) resolves domain names into associated IP addresses. One of the applications of reverse DNS is as a spam filter.
Because IP addresses are tedious to deal with and hard to remember, an IP address may also be assigned a host or domain name. You can think of an IP address as someone's physical street address and the host/domain as Bob's House. Multiple host/domain names can be directed to one IP address (as is often the case and referred to as virtual hosting). Host names may be looked up to find IP addresses, and vice-versa.
In common usage today, hostname refers specifically to the FQDN that comprises the name of the host, a period, and the domain name. The domain name is composed of labels that begin with the top-level domain and are arranged right to left for the second and, possibly, third level labels. The host name and the domain labels are separated by periods. The total length of the hostname as an FQDN cannot exceed 255 character with each domain name label having a maximum length of 63 characters. For example, if a company's domain name is "example.com." and a particular computer in the company has been named "plato", the hostname for that computer will be "plato.example.com.". Note, that technically FQDNs end in a period to unambiguously define the hostname and to be sure that it is not part of a longer domain name. (although in common usage this final period is often omitted).
Read More: What is a HostName?
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Lookup IP Address Location (Trace IP/Track IP)
This IP lookup tool is designed to provide additional information about the entered IP address. These details include the hostname, Geographic location information (includes country, region/state, city, latitude, longitude and telephone area code.), and a location specific map. The geographic details are pulled from a commercially available geolocation database. Geolocation technology can never be 100% accurate in providing the location of an IP address. When the IP address is a proxy server and it does not expose the user's IP address it is virtually impossible to locate the user. The country accuracy is estimated at about 99%. For IP addresses in the United States, it is 90% accurate on the state level, and 81% accurate within a 25 mile radius. Our world-wide users indicate 60% accurate within 25 miles (see results). By default this tool will lookup the IP address that you are using. You can enter any IP address in its place below.
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IP address
What is an IP address?
Every device connected to the public Internet is assigned a unique number known as an Internet Protocol (IP) address. IP addresses consist of four numbers separated by periods (also called a 'dotted-quad') and look something like 127.0.0.1.
Since these numbers are usually assigned to internet service providers within region-based blocks, an IP address can often be used to identify the region or country from which a computer is connecting to the Internet. An IP address can sometimes be used to show the user's general location.
Because the numbers may be tedious to deal with, an IP address may also be assigned to a Host name, which is sometimes easier to remember. Hostnames may be looked up to find IP addresses, and vice-versa. At one time ISPs issued one IP address to each user. These are called static IP addresses. Because there is a limited number of IP addresses and with increased usage of the internet ISPs now issue IP addresses in a dynamic fashion out of a pool of IP addresses (Using DHCP). These are referred to as dynamic IP addresses. This also limits the ability of the user to host websites, mail servers, ftp servers, etc. In addition to users connecting to the internet, with virtual hosting, a single machine can act like multiple machines (with multiple domain names and IP addresses).
