What ia na IP Address???
When you are on-line to the Internet, yah have a "real" "IP address" assigned to you, or to your NAT/router.. This address is like a telephone number, but one which can typically change [unless you subscribe for a static IP service] every time you dial up, or every time yah power cycle your modem or router. It is OK if it changes, because your Internet Provider knows how to find you no matter what IP address it assigns to you. The IP addresses are really just borrowed from your ISP when you are on-line. The Internet authorities have also reserved some IP addresses which are not 'supposed' to be used as real, and which are to be used by "private" networks. This is kind of like a "room number" as opposed to a street address. The post office doesn't know which room at the address the mail goes, you have to decide that.
An ISP can track, after the fact, which username is associated with an IP address, by interrogating the "RADIUS" logs which record when you sign onto the ISP, and what IP address you were assigned. If you have a cable modem service, they can associate the MAC address of your cable modem or your PC NIC with the IP address, so much the same effect is achieved.
This is a good thing for the health of the Internet. When another ISP reports to abuse to your ISP that you are becoming a terrorist, they can look in their logs for the time of the infraction and find out which user had that IP address. More and more, ISPs are terminating pain in the ass customers. Unfortunately the customer just goes and signs up with another ISP. There needs to be a blacklist of people who get kicked off ISPs, sort of like a credit report for Internet usage!!! There are already so-called "black lists" for those ISPs which seem to host too many SPAMmers. Unfortunately these people hide behind fake IDs in order to do their trash and are very hard to trace.
The IP address is listed in the "winipcfg" command of Win9X/ME, or the "ipconfig" command of NT4/XP/2K. The IP address is listed as a "dotted quad." That address is a hierarchical address, much like a phone number, which is split into area codes and local calling exchanges. XP and Win2K have a nice little GUI to report the IP address info status, if you enable the network icon to be displayed in the system tray (open network connections, and right click on your particular connection icon - select box at bottom to "show icon in system tray)
Most Internet "transactions" use names instead of the IP address numbers. This is where the domain name system (DNS)system comes into play. Whenever you type a web site name in your Internet browser, the browser must do a "DNS query" to find out the IP address corresponding to the name. It first looks in your own host file, and then it queries the DNS cache maintained on your PC, and then it asks the DNS server of your ISP. Once it finds this, it can use this number to form the IP packets to communicate with the web site. These names are "cached" for a period of time.
Private and illegal IP addresses:
Divide the types of IP addresses into three types, public, private, and "illegal." "Public" IP addresses are those which are accessible on the Internet. "Illegal" IP addresses are actually "public" IP addresses, but are used behind firewalls or proxies or NAT/routers, and are therefore NOT seen or advertised on the Internet. So I can choose the same IP for my internal network that Microsoft has for their www server, and everything would work just fine. "Illegal" just means that the address is not a reserved "private" IP.
The only real problem with using "illegal" addresses is that when some application on your PC attempts to resolve the IP address to a name, it goes out to the DNS server at your internet service provider in order to do this, so it actually resolves to whomever owns the real name. If these are addresses that you will never use, yah can always enter them into the hosts file on your PC, since it looks in the hosts file before it attempts to resolve the name using the ISP's DNS server.
The Internet committees, actually the RFCs, has designated a subset of the IP addresses as "private" IP addresses, and should be used by these private networks that are not visible on the public Internet. These IP addresses should never be routed by routers within the Internet. There are three of these IP address ranges allocated:
10.0.0.0/8 = This is a private class A address, commonly called a "10 net.
172.16.0.0/18 = This is a reserved class B address.
192.168.0.0/24 = 192.168.255.0/24 These are 255 class C reserved IP spaces.
So this is why the IP address of your NAT/router is typically 192.168.1.254. They are using the assigned private IP space.
There are actually other kinds of IP addresses not to be discussed, such as "Multicast" IP addresses, from 224.0.0.0 and up. And there is a really funny address that your Ethernet NIC will "assume" if it cannot acquire an IP address from a DHCP server. This address looks something like "169.something."
Actually it is pretty simple stuff. It is all hop by hop. If I know the IP address of Joe in CA, which I get by using the domain name service, then I just send the packet to my gateway, who forwards it on into the Internet routers, who have the collective knowledge to get the packet to Joe in CA.
When you are on-line to the Internet, yah have a "real" "IP address" assigned to you, or to your NAT/router.. This address is like a telephone number, but one which can typically change [unless you subscribe for a static IP service] every time you dial up, or every time yah power cycle your modem or router. It is OK if it changes, because your Internet Provider knows how to find you no matter what IP address it assigns to you. The IP addresses are really just borrowed from your ISP when you are on-line. The Internet authorities have also reserved some IP addresses which are not 'supposed' to be used as real, and which are to be used by "private" networks. This is kind of like a "room number" as opposed to a street address. The post office doesn't know which room at the address the mail goes, you have to decide that.
An ISP can track, after the fact, which username is associated with an IP address, by interrogating the "RADIUS" logs which record when you sign onto the ISP, and what IP address you were assigned. If you have a cable modem service, they can associate the MAC address of your cable modem or your PC NIC with the IP address, so much the same effect is achieved.
This is a good thing for the health of the Internet. When another ISP reports to abuse to your ISP that you are becoming a terrorist, they can look in their logs for the time of the infraction and find out which user had that IP address. More and more, ISPs are terminating pain in the ass customers. Unfortunately the customer just goes and signs up with another ISP. There needs to be a blacklist of people who get kicked off ISPs, sort of like a credit report for Internet usage!!! There are already so-called "black lists" for those ISPs which seem to host too many SPAMmers. Unfortunately these people hide behind fake IDs in order to do their trash and are very hard to trace.
The IP address is listed in the "winipcfg" command of Win9X/ME, or the "ipconfig" command of NT4/XP/2K. The IP address is listed as a "dotted quad." That address is a hierarchical address, much like a phone number, which is split into area codes and local calling exchanges. XP and Win2K have a nice little GUI to report the IP address info status, if you enable the network icon to be displayed in the system tray (open network connections, and right click on your particular connection icon - select box at bottom to "show icon in system tray)
Most Internet "transactions" use names instead of the IP address numbers. This is where the domain name system (DNS)system comes into play. Whenever you type a web site name in your Internet browser, the browser must do a "DNS query" to find out the IP address corresponding to the name. It first looks in your own host file, and then it queries the DNS cache maintained on your PC, and then it asks the DNS server of your ISP. Once it finds this, it can use this number to form the IP packets to communicate with the web site. These names are "cached" for a period of time.
Private and illegal IP addresses:
Divide the types of IP addresses into three types, public, private, and "illegal." "Public" IP addresses are those which are accessible on the Internet. "Illegal" IP addresses are actually "public" IP addresses, but are used behind firewalls or proxies or NAT/routers, and are therefore NOT seen or advertised on the Internet. So I can choose the same IP for my internal network that Microsoft has for their www server, and everything would work just fine. "Illegal" just means that the address is not a reserved "private" IP.
The only real problem with using "illegal" addresses is that when some application on your PC attempts to resolve the IP address to a name, it goes out to the DNS server at your internet service provider in order to do this, so it actually resolves to whomever owns the real name. If these are addresses that you will never use, yah can always enter them into the hosts file on your PC, since it looks in the hosts file before it attempts to resolve the name using the ISP's DNS server.
The Internet committees, actually the RFCs, has designated a subset of the IP addresses as "private" IP addresses, and should be used by these private networks that are not visible on the public Internet. These IP addresses should never be routed by routers within the Internet. There are three of these IP address ranges allocated:
10.0.0.0/8 = This is a private class A address, commonly called a "10 net.
172.16.0.0/18 = This is a reserved class B address.
192.168.0.0/24 = 192.168.255.0/24 These are 255 class C reserved IP spaces.
So this is why the IP address of your NAT/router is typically 192.168.1.254. They are using the assigned private IP space.
There are actually other kinds of IP addresses not to be discussed, such as "Multicast" IP addresses, from 224.0.0.0 and up. And there is a really funny address that your Ethernet NIC will "assume" if it cannot acquire an IP address from a DHCP server. This address looks something like "169.something."
Actually it is pretty simple stuff. It is all hop by hop. If I know the IP address of Joe in CA, which I get by using the domain name service, then I just send the packet to my gateway, who forwards it on into the Internet routers, who have the collective knowledge to get the packet to Joe in CA.
