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How an ISP assign a public IP address to a client?


I want to have an idea how an ISP assign a public IP address to a client? any clear idea please?

Thank you
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Lee W, MVP
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It depends on the ISP.  They likely have provisioning systems that just pick one (or a block) and assign it to you... Assuming you mean static.

If you mean dynamic, then they use a DHCP based system to assign you the IP address.
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@leew: thanks but how they assign it ? that's what i want to know. the method!!! and yes i'm talking about static IP
What you're asking is still not clear.  How do they assign it to who?  To you?  To your equipment?  Can you give a context as to why specifically you need this information?
They assign it by picking a number from their pool and reserving it for your specific network equipment or login. The mechanics vary ISP to ISP but they might, for instance, link your MAC (unique id assigned to all Ethernet devices) to the IP; or they might assign it as your 'modem' logs in...
Unless you're using a T1 or other type of connection that doesn't use a modem.  Then they may program the router directly... or they may DO NOTHING other than "designate" that IP for you.
all your answers are not clear, ok, imagine, i went to my ISP, i asked them, please i need a static IP for my server, they said ok Sir, you got it.

What the steps they do so they assign you the given static IP? are they routing the Static IP through the DSL line ? through the phone line ? through your internet login ? how they route it? I can't go to my TCP/IP parameters and put their any Public IP I want, it must be assigned by the ISP, so how they route it to me? to the modem? to the router? the phone cable line or my internet login?

Thanks and sorry for any confusing.
First they select an available number from their pool of addresses. ISP's are allotted a block of addresses they rule by IANA - Internet Assigned Numbers Authority). Once that number is 'yours', where it goes is up to you. They might tell you to 'put it in there' (meaning your router) or they might ship you a router (or modem or whatever that device is); or they might assign it to you when you login with the agreed to login and password. Bottom line is, the ISP is the authority on which number you might get. What you do with it (within the ISP's 'acceptable usage policy') is up to you.
I still need an answer from someone work with a service provider, i know all what you said dear @raoool, i need something new, a kind of configuration for exemple or something.
everybody here answered correctly
There is no configuration, only how routers route, ex BGP.

Its the same as giving you pc a static ip address on your LAN !
There is no configuration.

If You look at your current Network LAN design, when you plug you pc into (a switch) on that network
You (A) give your pc a static ip (B) Get a ip from the dhcp server on the lan.

This is the exact same thing that happens when you plug your equipment into the ISP network.
@kwolbert_IT: ok hold on, DHCP is another process, users do a DHCP Request and accept any given Dynamic IP from the DHCP Pool, But how they configure your static IP? and No your answers are not clear for me. Sorry for that but i need more clarification, and what about the ex BGP ?? what are you talking about man? External BGP is only for the purpose to let routers communicate in external AS. doesn't have anything with static IP.

So Expert: how they configure a static IP for a customer and route it to that user.
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Syed Muhammad Usman
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a part from above i would llike to add one thing that in any case you would not be able to change ISP IP Address.
@Syed_M_Usman: Your answer is good, i think i understood how they do it, so they map the the static IP with the user login / phone line.

What did you mean with " PTP lease line connection " are you talking about Frame Relay? no?

Do you have any sample configuration of mapping a Public static IP with an ADSL line?

Thank you very much.

if you got the answer, i would suggest you to close the case.
Syed_M_Usman:any configuration exemples?
sorry dear i dont have, but see bwlo link this may help
Hi David,

Have you ever registered an automobile and got a license plate for it?  You walk up to the counter, fill out the paperwork, hand them the required payment, and they hand you a license plate from the stack behind them.

Getting a static IP is exactly the same.  The ISP has a "stack" of license plates (IP addresses) and hand you any one of them from the stack.

@Kdo: it's exactly what i'm talking about, i mean, you request a public static IP from the provider and you pay about $15 to $20/monthly and you get it. Then they map it using your phone line, please correct me if i'm wrong.
david you are right, as i wrote in my post

The media may be your phone line (could also be satellite, cable, etc.) but that's all that there is to it.

thank you and sorry for the long thread, but that [deleted] @kwolbert_IT wasted our time.

Adjective deleted.  Kdo

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you are welcome