Questions about private/public IP addressing

hi guys..
long time since i last posted here, i dunno if this is the site for me to be posting this question on, but i dont want to go to another site n register to post, im familiar with this place, and im sure a lot of u guys can help me out

my question is on public and private IP addressing, its been confusing me..
i know wat they are, i wanna know who assigns the addresses..im using a wireless router, and i know my router has a public and private address..my ISP dynamically assigns both these, right? '

then, my computer also has a private IP and a public IP address..my private IP address has been the same and is always the same..and when i run ipconfig /all, i get the same ip address, but DHCP is enabled, and the dhcp, gateway and dns server are all pointing to the same IP address..when i browse this ip address, i see my routers gateway summary..so my question here is, who assigns the private address? the ISP's DHCP server? coz dhcp IS enabled for my private address too...as u can see, im very confused here..

im doing my MCSE course at the moment, and im able to apply this into a corporate network and scenarios i'd find in an exam but i cant figure out how this works in my home environment..please reply! thanks a lot

 

Your public IP address is assigned to you by your ISP. It may be constant, or change now and again.

Your private IP address(es) are assigned by your router's DHCP. Also, in the configuration of your router, you may be able to change the private IP address of the router itself.

This can get a little more convoluted if you have a MODEM/Router from your ISP and another router (i.e.: wireless, perhaps) plugged into it. It is usually best to set the ISP router up in "bridge mode" so that NAT does not occur twice and so that DNS flows properly.

Private IP addresses are usually in the 192.168.xxx.xxx range. I changed the private IP addresses of both the ISP's MODEM/Router and my own wireless router and limited the range of IP addresses each can give out via their own respective DHCPs.

If you do not have the manual for your wireless router, download it. It will all make more sense with that tidbit of information.

 

thank u so much for that!
ok, i have a wireless modem...so there's no two things connected...i have a couple more questions though..
i notice that my router also has a private and public IP address..i know that the router's private address is constant, usually 192.168.1.1, i think...but who assigns the router's public IP address? the ISP? does the ISP's DHCP lease IP addresses to both the computer and the router?

i thought i had more questions but i guess i dont also, wat would my router's manual help me find? thanks
EDIT: ok, i got my manual and its helped already lol...i found the answer to my above question, that the ISP assigns public IP address to my router too...thanks for the help...if anyone can add anymore info to clear this up, like explaining how the router (gateway) works with the computer and the ISP, please post here, i'd really appreciate it...thanks

 

hi, one more thing...how do i view my computers public ip address, or change (renew) it? i mean..ipconfig /all displays the private ip address and the default gateway/dhcp pointing to my router..how do i view public ip etc? thanks!

 

Public means that your computer will not trust any computer around, this is a good feature to use when you are at a hotspot or in public. Private is when you can trust the computer around, when you are at home for example.

 

If you dig through your routers setup page you should find a section that will give your public info. Normally this is in the ISP setup section for the WAN, aka connection status. Then in the same config section you will find the private info 192.168.1.1-50. This is where you change you private info, subnet or change to the 10.x.x.x IP as some of the bussiness class hardware uses. If you change this all of the pc and gateway info will change with it. Router requires a reboot, then all pc must to a release and renew to get the new IP. You will also need to remember to change your address in you browser to the new IP. I never leave any thing at def for security reasons. This way if something is messing up it's a little easer to detect. One other thing. Some routers do some internal bridging in which IP address are remapped. Part of an advanced FW features and whether it has a NIM in it for coax use. All of the hardware I have actually report the ISP DNS servers not the gateway IP.

 

Probably the easiest way is via the internet. Try a site like this. Of course, your router always knows the public IP address as well. Unless you have requested (and usually paid additionally for) a static IP address, your ISP will lease you a public IP address that usually changes every time your MODEM is power cycled.

 

thanks for the above stuff ^ ^
so i was under the impression that my router is assigned a public IP address, and also my computer is assigned another public IP address..is this the case?

coz i visited the site mentioned above..and it gave me my public IP address..
then i went to my router's page and the internet address was the same (i believed that the router's summary page/connection status page shows the router's public IP address)...please help me understand this bit..
EDIT: i have another laptop connected to the same router..so i viewed my router's page on it too, and it showed the same public IP address..so does this mean that the router is given one public IP address for however many computers connected to it?

lastly, to renew a public IP address..typing ipconfig /release and /renew will renew my private address, right? will that also renew my public address? or will i need to turn off my router and turn it back on again? thanks!

 

Depending on which page you are viewing, Yes you can see your public and Private. Now is your public IP a Private IP address. Some ISP do this to prevent servers from running, others do it to save the Public IP for the business and those who want to pay for a public IP.

No, you can not reset your Public. This is controlled by your ISP. Some networks are so busy every time you reboot (router) you will get a different one. Some after 10+min of disconnect. And some never due to MAC addressing controlling.

Your router does what is called a NAT. This means all that is seen by the outside world is your Public IP, no matter how many private IP (PC) you are running.

 

Read What is a router

 

thanks for that..very helpful..sorry, as u can see, my knowlege is a bit incomplete so just to clarify, my router is NOT assigned a separate IP address, right? it kind of translates all my private IP addresses using NAT to one public IP address..is that basically it?
EDIT: my private address is in the 192.168 range, and my public IP in a public IP range

 

please reply, someone

 

You finally got it. Private you control, Public your ISP control. The router just allows you to share 1 Public IP address.

 

thanks a lot..i was very confused over this, but again, this forum has helped me understand

but the ISP assigns the public IP address to the router first, right? then the private PCs connect to the router which translates their private IP address to the one public IP?

and lastly, do all routers use NAT? do all ISPs use the method that my router does? if not, how will that work?
please reply both my questions, someone

 

To communicate with the outside world the TCP/IP protocol use a source and destination IP address, the IP address leased to you by the ISP is the source IP address and the destination IP is the web site you are trying to reach. Your router using DHCP protocol will assign an IP address to your computer, this IP address won't be seeing by anyone in the Internet as it is not used by the router to communicate with the exterior, the router will actually correlate your computer's IP address with your MAC address, which is what he uses it to communicate with any network element connected to it.

I think you have a confusion about NAT, please read this http://www.chicagotech.net/nat.htm and tell me if you are clear.

NAT can give you more flexibility to assign IP addresses but is more complicated to setup, a DHCP server is as easier to setup as just enabling it, and DHCP is ubiquitous in today's networks.

 

thanks for that ^^
so firstly, any network connected using a router has to use NAT, or ICS (as i saw in the link u posted) to connect to the internet, right?

the source/destination IP addressing helped me better understand wat IP address my ISP leases...
i know my router's DHCP assigns a private address to my computers, but im not sure wat u mean about the router using my computer's MAC address to connect to external networks..i thought basically the router translates the private addresses of ur computer(s) using NAT into one public address?
i think ive got pretty much everything now, thanks for ur help..if u can just clarify those points, that'd be great

 

What happens is that a router really deal with the form of an IP address only, it deals with an specific network, whereas a switch deals with MAC addresses. Today's home routers are really a combination of of the pure router and switch, the router functionality will send source packets to the destination network using the IP address and its switch functionality using the MAC address of the network card (NIC) will redirect the packets to the appropriate computer.

 

thats very helpful, i understand now..i was just confusing the fact that the public IP address was assigned specifically to my COMPUTER or to my ROUTER or something like that...now i understand that it is simply assigned to my private network, and the router uses it and allows my private network to share it to communicate on the internet (i find it easy to understand when i try to explain myself lol)...thanks a lot