how ISP allocate ip address for my pc.?

It is granted by the computer god( s ) .

It is granted by the computer god( s ) .

ip address secured your works, if any body enter your pc that can be identified. on the other hand, if any one do some thing bad by your pc then it helps to identified .

It is granted by the computer god( s ) .

You ISP allocates one IP address to your Router. This is called your external IP address, and that's the one the rest of the world sees.

Your router then allocates as many "internal" addresses as you need for your computers, and handles the packets coming and going from the various machines using a system called NAT (Network address translation)

Your internal address is controlled by you (you can control this by the setting in your router) and should be one of the address ranges that are reserved for "private" network, like 192.168.x.x or 10.1.x.x. Because those addresses are never used by the rest of the internet you don't get a conflict.

Your modem has one IP address from the ISP. You router is assigned this address by the modem. You router creates a subnet and assignes new, unrelated address to all other devices that connect to it.

You could add a second router to your first and your 1st would assign one of those address to it. Then you can set that router to have its own list of subnets, separate from the other and connect to another group of devices. You can either set it up so the devices on both networks can communicate with eachother or make it so they cannot.

So your router is managing it. It uses a network translation to multiplex the single IP your ISP gave you.

You issue a connect to say, yahoo port 80. The source is your PC(private ip) random port. So you are sending from your private ip/random port to yahoo port 80. The router rewrites that to Router's IP/Router's random port destined for yahoo port 80. It remembers the source mapping, your ip/yourrandom port and its ip/its random port.

Yahoo doesn't care, it sends back a response to the the Router's IP/ Router's random port. Your router captures that, rewrites the destination to the mapping back to your client (your ip/your random port).

In this way, you can hide as many private ips behind a single publicly routable ip. There is a limit because each NAT takes a bit of persistent memory and each NAT needs to be looked up (takes time when the table is large).

Inbound, that is when it gets testy. That is why there are things like port forward or DMZ to map the inbound to a particular private ip/port.

You will most likely have a single public IP address for all your devices. It will be dynamically allocated to you when you access the Internet. The address will be shared thru NAT across your different devices, each of which will have their own private IP address on your network.

They don't their local home hub does this. The ISP allocates the IP address for the hub not your PC all traffic going out to the web goes thru the hub which has a unique IP to them - they may the proxy all traffic out of their network into the WWW. This is all true UNLESS you specifically asked them for a fixed IP address as part of you internet contract. If you did not then you IP will be something like 192.168.x.x and your ISP hub will be something like 192.168.x.254 (or some such similar high digit set at the end - that is if they are using IPv4. If the are using IPv6 then these number are different.

So you home hub is acting as the DHCP provider for your home network devices.

First off, the mechanism is DHCP. Now, the remaining questions are

How does assignment work?

Did I get a public IP address?

Is it static?

Assignment is pretty much up to the ISP. A strict ISP is going to be maniacal about tracking every single piece of equipment on the network, maintaining a database about all subscribers and MAC addresses and then doing an assignment for that subscriber from the appropriate prefix.

Most ISPs are still using public IP addresses, but this is not a requirement. It would be very easy for an ISP to put all of their subscribers behind a carrier-grade NAT system. I’m pretty sure there are a few folks already doing this. So, your IP address may be out of RFC 1918 space and thus not usable externally.

ISPs seem very loathe to assign a static IP address. If nothing else, they charge more for them. However, they don’t seem to commonly let addresses float either. An ISP that was desperate for address space could easily reuse addresses when subscribers are not active.