I saw some confusion on another thread with regards to IP addresses.
Any 1 home network may have numerous IP addresses being used. You must understand that there are INTERNAL IP Addresses and EXTERNAL IP Addresses. Internal IP addys almost always begin with 192.168 - though they can be configured in different ways through a router.
To know your EXTERNAL IP ADDRESS go to www.ipchicken.com. Websites will typically record these IP addresses in the same manner this site reports it to you.
To know your internal IP Address go to a DOS prompt - hit START -> RUN , type in "cmd" and hit OK. Type in "ipconfig" and hit ENTER. The 2 IPs worth noticing are your IP ADDRESS and DEFAULT GATEWAY.
HOW IT WORKS- CABLEMODEMS, ROUTERS, AND DHCP
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The EXTERNAL IP addy is the one which is assigned to your specific internet address by your internet provider. Only rarely does a PC yield an IP address that is the same as its external IP. One such case is if you have a cable or DSL modem which has a single ethernet cable connecting it to your PC.
When your cablemodem connects to your ISP, an IP address is assigned. This IP address will be your identity according to all the websites you visit. This is similar to how DHCP works, will explain later. If your cablemodem is connected directly to your PC, then your internal & external IP address will be the same. You will have no internal network - the only network will be that provided by your ISP; thus, only 1 IP address will exist.
Unless you are paying for a static (non-changing) IP address, those numbers are likely to change. Sometimes they change every time your cablemodem reconnects. Sometimes they change even less frequently. Most ISPs will offer the ability to have a static IP for $7-$20/ month.
Introducing the router..
Your router acts as a GATEWAY between your internal network and the external network. Consider a network where a router is connected to a cablemodem (external network) and 2 PC's. 2 networks now exist - the internet & your home network.
When you turn your router on, it communicates with the cablemodem in order to determine the IP addy assigned by your ISP. Your external network is now defined.
It then communicates to each of the PCs which are connected and utilizes a DHCP service to assign an IP address to each of them. Usually, the first PC gets 192.168.1.100, the second 192.168.1.101, etc etc.. This process defines your internal network.
When your PC talks to another PC within your network, only the internal IP addresses are used. The internet has nothing to do with this traffic - it is all contained internally within your router. (fellow geeks, not going into tcp/ip comm vs standard MS filesharing protocols.. but i know, ok..)
When you go to a website, your PC communicates through the internal gateway exposed by your router. Back to IPCONFIG. The DEFAULT GATEWAY IP address is the IP address of your router. You can open up Internet Explorer and type in that IP address, and most likely you will be connecting to your router.
When you go to a website from either PC, the IP tracked by that website is the same regardless of which PC is doing the talking.
192.168.1.100 (PC 1) sends data to the gateway (router) 192.168.1.1
The router sends that chunk of data to the cable/dsl modem, which in turn sends that data to a website.
When the website returns the information, the data still contains the IP address of the original sender.. So the router gets the data, and then reads each packet of data to ensure data is returned to the appropriate PC 192.168.1.100.
A website does not know what sits behind the router. (cookies come into play here, but I am talking about IP addresses only) Whether you use PC 1 or PC 2 in this scenario, a website is most likely not going to know the difference.
Most routers provide the ability to allow programming via the internet, but only if you know how to turn the feature on. Most wireless routers also disable configurations from wireless clients.
FIREWALLS, PORT FORWARDING..(also called pinholes)
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PCs communicate to one another through ports 1-65535. Standard website traffic uses port 80. Your router closes most ports, other than 80 & several other commonly used ports. Firewalls allow an additional layer of protection.
Some applications require that certain ports be open in order to function properly. MSN Messenger file transfers, gaming, FTP servers, filesharing apps, and PC Anywhere are several of countless numbers of applications which require you to open up ports in order to allow proper functionality.
If you have a PC sitting behind a router, with a firewall running - the router AND firewall need to be aware of this specialized traffic. Your router, in addition, needs to know which PC to send this specialized data to.
For example. If you are running an FTP server - which uses port 21 - your router will need to know the internal IP address of which PC is running that server. You tell your router to forward all traffic on port 21 to the PC using internal IP address 192.168.1.100. On that PC's firewall, you will also need to open up port 21 or add that application to the exception list so it may open up the ports.
This procedure is called "CREATING PINHOLES" on some routers, as you are essentially defining how traffic coming to certain ports is to be routed to PCs on your internal network.
DYNAMIC DNS/ PROXY SERVERS
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A DNS server translates an address such as www.yahoo.com to its IP equivalent. A simple example of this can be viewed by the PING operation. A PING simply sends a small packet to an IP address and tells you how long it takes to receive communication back.
Open up a DOS prompt.. START -> RUN , type in CMD and hit ok.
Type in PING www.yahoo.com
You will notice right away that a DNS server contacted by your cablemodem translated www.yahoo.com into an IP address.
Now lets say you want to run some sort of website or filesharing service, or maybe you want the ability to access your PC remotely through LOGMEIN or PCANYWHERE or any number of applications designed to allow such an ability. Unless you are paying your ISP for a STATIC IP, then you cannot guarantee that while you are out of town for 2 weeks that you can use the same IP address.
Here is where companies like DYNDNS or DNSALIAS come in handy. They will provide an application which tells your PC to communicate its network IP address to their web server at predefined time intervals. They also allow you to give your PC a name.
This way, when I tell my laptop in Podunk, Alabama to connect to my home PC, I merely tell it to connect to mykulwayne.dyndns.com. The address is looked up, whatever it may be at the time, and my laptop is provided the exact IP to use for connectivity.
Proxy servers act in a different way. They aim to maintain anonymity through your web surfing - you can find reviews here ->
http://www.topfreeproxy.com/ In much the same way data goes from your router to your cablemodem, another layer is added to communications - this layer exists after your cablemodem and before your data gets to a website.
BEFORE PROXY:
PC -> ROUTER -> CABLEMODEM -> WEBSITE
AFTER PROXY:
PC -> ROUTER -> CABLEMODEM -> PROXY -> WEBSITE
This way, the website is only aware of the IP address exposed by the proxy server. The IP address of all appliances prior are hidden.
Hope this helps..
Another service by your local geek,
MykulWayne
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Edited by MykulWayne at 04/08/2008 11:21 AM PDT
