Can't change my internal and external ip addresses

Whats is ipconfig /flushdns supposed to do?

The release is for taking away the current ip address and return it to the dhcp's ip address pool so to become avialabe again if sdomeone requests it?

Am the renew for takign a new one? But as the word says it must be a NEW ONE not the current one i always be given when i just do release in the previous step.

But the router's built-in dhcp server has a tendency of giving the same one agian if we have it to automatc . why is that? Manually i can set it to get 10.0.0.2 instead of 10.0.0.1 all the time but why not automatically?

Also i want to change my external ip address(the routers one) since i have dynamic contract with my ISP but no matter how many tiems i reboot i always get the same one, 83.171.225.52.

Anyone knows why?

Reply to
Nicky
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Deletes the contents of the DNS resolver cache on your PC.

Renew means renew the lease, the IP address will not necessarily change. You will get the same IP as far as possible. If you haven't had an IP lease for a long time (maybe days) then that IP could be assigned to someone else and then you will get a different one.

You will get the same IP address with a new lease.

Because that's how DHCP usually works. The MAC address (Physical address) of your network interface and your host name can all be used to identify your equipment and re issue the same IP.

It depends on what control you've got over the DHCP server and whether or not you can tell it to issue a particular IP to a paricular MAC/host

This is normal. Why do you want to change it? Dynamic does not mean that you get a new IP address every time you connect, it means that the IP address is assigned by DHCP. DHCP will usually try to give you the same IP address as far as possible because this causes minimum disruption to your connection.

Jason

Reply to
Jason Edwards

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Why not?

Why?

Why not?

Yours, VB.

Reply to
Volker Birk

Why we want to do that? The contents of the dns resolver would cotnail the primary and secondary ip addresses of our isp. By flush it we mean clear it? Delete it? What good comes out of that? If we do this thwn our web pages could nto be resolved. I just dont understand the use of it.

Is this correct?

I see. I tough that ipconfig /renew would just give me a brand new ip address to use thats why i though it called renew, but i see now its for the lease of the current ip address i was using before i ipconfig /release it.

But what if i wanted a different one for example 10.0.0.2 or anyhting random ie. 10.0.0.50?

The way ti works now i woudl always get 10.0.0.1. This is because the dhcp server will assign the firt available ip addres of the ip pool?

I have only 1 pc and iam experimenting with this things and i have set the lease for ever. This emans that in autmatic mdoe i wont be abel to get an ip differnet that 10.0.0.1? How can i change that? (except of doign that manullay)

So ipconfig /release clears my current ip address and i have nothing and then ipconfig /renew gives me the same ip address with a ne lease.

2 questions.

a) How does it know what was the previous ip address i had before i ipconfig /release it? Does it store it in someplace?

b) When we ipconfig /release then we say we get new lease. Does that mean that we get the same lease we had before but just the time starts from the beginning, so if it was for 1 week we ghet a lease for a whole 7 days while before doing that maybe we where in in the middle of our current lease week?

But sicne it can identify my NIC(cause of the hardware address) and the PC(cause of the hostname) then it always can identify my specific equipment. Changind the ip address wouldnt make a difference, would it?!

I have full control sicne iam the admin but i just want to know if ti can be done in an automate way. Manually yes i know it works.

Thank you for correcting me, this was indeed what i and many other peple though when someone told us it had an Dynamic ip address, that i would change on every rebbot of the machine or the router.

By DHCP you mean the ISP's DHCP server right in a same manner as we do when we set our router's built-in dhcp to assign ip addresses for our internal hosts. Correct?

And if yes, we get this same ip address for how long? Until the ISP's lease value for our ip address expires?

minimum disruption to your connection? Umm, how you mean please?

Sorry for my too many questions, but i need to get enlightend :-)

Reply to
Nicky

'We' want to do that, i.e. if the contents of the cache are outdated but the TTL is not.

Yes.

Only the contents of the cache, which is filled again with the next request.

Then you have to configure the DHCP server.

Yes. At least in RAM.

No, it wouldn't.

Usually: yes.

That depends on the DHCP server of the provider and its config.

Yours, VB.

Reply to
Volker Birk

?/? Jason Edwards ??????:

It's just a temporary store of DNS results so the number of external DNS requests made by your PC is not excessive.

ipconfig /release releases your lease on the IP address you had.

Then you have to be able to tell the DHCP server to issue the address you want. It may or may not be possible to configure the DHCP server in your modem/router to do this.

You probably can't make DHCP issue a different address each time without manual intervention because it just doesn't work like that.

It does.

Yes.

Usually you will get a new lease of the same IP but the exact behaviour depends on the DHCP server. It's not unknown for broadband ISPs to have variable lease times because some customers want a continuous connection and some want it for only a few minutes each day. Sometimes the lease time gets longer after the first renewal which usually occurs half way through the current lease. If the IP changed at renewal time then a lot of people would be very upset because any connection in progress at the time would be lost. So DHCP tries not to change the IP when the lease is renewed.

It may not make a difference to you but changing the IP address at lease renewal time would upset anyone with a download in progress at that time.

Yes. There is a DHCP server at your ISP which issues your router with an IP address. Your router has a DHCP server which issues IP addresses to your own PCs.

When I last used a dynamic IP myself the IP address changed at random times when the ISP expanded or changed their network. This could be at intervals of months or years.

Most people like to have the same IP address all the time and may have set up DNS services which depend on it remaining the same. Even if you have a static IP your ISP may assign it by DHCP.

Jason

Reply to
Jason Edwards

As we talk the fog of understanding these gets out of the way and i finally start to see some light and i thank you for that! :-)

So i generral i understand that:

( i understand the lease as assignment)

a) ipconfig /release release my lease on the IP address i have and also discards my current ip address leaving my NIC unassigned.

b) ipconfig /renew gives me the same ip address with a new lease. It never changes my ip address the time it gets renewed.

So as a logical conclusion we can say that what distincts a Dynamic IP assignment configuration from a Static IP assignment configuration is the lease renewal times?!?

The Static configuration actually has an infinite lease time and never gets renewed while the Dynamic one has a time specific lease specified by the admin of the dhcp server? Can we say this is the case?

But then again iam confused with the fact that ip addresses never change at renewal times so i think i still miss what the lease times are created for because clearly they are not to be meant to change out ip addresses.

Reply to
Nicky

actually, they map the MAC of your modem to the IP address they've assigned.

Reply to
Jeff B

So Jeff, this is like manually assigning the ip address they want to our modem/router just like what we do manually to our NIC, isnt it? :-)

Reply to
Nicky

It was stated in my first post that MAC addresses are used. In the case of Nicky's service I suspect that you are correct and the MAC of the modem is used, but this is not the case for all broadband service types. Some types of broadband service do map it to the MAC address of the customer's network interface which in the case of a home user is likely to be a PC or a NAT box.

Jason

Reply to
Jason Edwards

Jason could you please answer my latest question pleaser so i can clear this things in my head?

Thank you.

Reply to
Nicky

DHCP and lease times allows your ISP to assign you an IP address of their choice (from their allocated ranges). If you haven't paid the bill you may find that you either get no lease or no renewal of current lease. DHCP maps your MAC address to the IP address assigned to you. The DHCP server stores this mapping so it can recognise you even if you haven't had a lease for longer than the lease time. All MAC addresses are different (in theory) so the DHCP server recognises you by your MAC address and assigns you the same IP address. Manual intervention by your ISP (replacing or reconfiguring the DHCP server, reconfiguring or expanding their network etc) _may_ cause your IP address to change. This may not happen often. With a dynamic IP there is no way for you to know when your IP address will change. It may change often or it may change every few years. The average home user will not notice that their IP address has changed and does not need to do things which require a static (never changing) IP.

In the case of the DHCP server in your own router, you can configure it to map local IP addresses to the MAC addresses of your PCs in any way it's capable of.

You can find further information here:

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Jason

Reply to
Jason Edwards

I still dotn understand whats the lease all about if its not for changing ip addresses.

Please can you answer in the questions i made in my previous post?

If you answer to what i asked ui can understand better.

Reply to
Nicky

Read the RFC. In particular the paragraph which begins: "DHCP supports three mechanisms for IP address allocation."

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Your ISP decides which method they want to use for your service. Even if dynamic allocation is in use you will not necessarily get a different IP. If your previous IP is still available and has not been assigned to someone else then you will get it back. If you still have questions after you've read the RFC let me know.

Jason

Reply to
Jason Edwards

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Reply to
Nicky

Try "2.2 Dynamic allocation of network addresses" Without a lease I can't see how it would be possible to be sure that a client has "been retired" (Doesn't need an IP because it no longer exists).

DHCP can assign a permanent IP

2.2 "Even when assigning "permanent" addresses, a server may choose to give out lengthy but non-infinite leases to allow detection of the fact that the client has been retired."

My own box which is connected to my modem has a permanent configuration and does not use DHCP. However I can also use DHCP if I wish. If I change it to DHCP then I get exactly the same IP configuration with a long lease. I've forgotten the lease time it gives, I think it's 1 week. This doesn't mean I'd lose my IP after a week because after a few days the box would have a chat to the DHCP server about letting me keep it longer. I wouldn't notice this unless I was watching for the DHCP packets.

I think 2.2 clears this up.

See 3.1 etc As previously stated DHCP will do its best to leave you with the same IP. If you leave your PC (or router) on then it will keep the same IP forever unless your ISP decides to tell the DHCP server to force a change or deny you an IP address.

I think it may be best to just accept that you can't change your public IP address. You can't assume it will never change but changes are likely to be rare. Changes are more likely if you leave your equipment powered off for a few days but this does not mean it will definitely change.

Jason

Reply to
Jason Edwards

If you have a ISP that provides a static IP, yes. They will have a record of your MAC address (from your NIC, your router, or your modem, it doesn' tmatter), and will reserve an IP address specifically for that MAC address.

If you have a dynamic IP, the automated system will TRY to give you the same IP each time your lease is renewed. Again, the ISP has your MAC address on record, and it will try to give you the same IP you had before the lease expiration, as long as somebody ELSE didn't claim that IP first.

In general, if you are in the position to care about your IP address, you generally don't want it to change often, if at all.

Reply to
Ryan P.

Using DHCP, you _can_ get another IP address next time you request another lease. There is no guarantee for this - you could get the same again.

Yours, VB.

Reply to
Volker Birk

But Jason in a former psot said that no matter if the lease tiem renewal comes i will still have the same ip address otherwise the current communication i may be having at the moment would be disrupted.

So from that he clearly states at "If you have a dynamic IP, the automated system will TRY to give you the same IP each time your lease is renewed. Again, the ISP has your MAC address on record, and it will try to give you the same IP you had before the lease expiration, as long as somebody ELSE didn't claim that IP first. "

Claim it when? The time i was already using it? Even if he did, the server woudl deny it, and even if the lease renewal tiem comes upa gain it will take a sec before it get renewd to the same again. So there is no time for someone ELSE to take the ip address.

You have static ip = no dhcp/ manual assignment/ infinite lease time You have dynamic ip = dhcp assigned/automatic assignrmnet/has lease time You have static ip assigned by dhcp = ip reservations/no lease time == mappign the mac to the specific ip address.

My isp very well may be doing the ip reservations for the wan interface of my router/modem which is why iam always getting the same ip address.

But lets see examine all 3 cases:

1st case iam not for sure because i have a contract for dynamic ip addressing not static otherwise i would pay more and in 6 months now my ip address changed one time. So its not number one. Also the isp coulnst manully configure my modem/router :-) which can happen though by distance on case 3.

So thats leaves us 2 and 3 cass. Which one?

I thought i was number 2 but wouldnt my ip change every time i connect or so as it does with other friends of mine that also have dynamic ip addressing? But in their case they have an adsl modem not an adsl modem/router, maybe that matter too.

In case 3 of mapping(which i tend to beleive i have cause my ip changes every 3 months or so) wouldnt that fal to case 1 again which is static with the difference that it wont have a lease time?!? But then again i didtn pay for a static one although i like it!

ok i start to sound crazy again! Like iam on a labyrinth or something :-)

Also tell me a case that i could lose my dynamic ip address i usuallly have 3 months now in my case 83.171.225.52.

3 m "Without a lease I can't see how it would be possible to be sure that a client has "been retired" (Doesn't need an IP because it no longer exists). "

Cliant has been retired = client either switced off his comp or disconnected from the network?

In those cases the server waits the lease time to check and free the "retired" ip address back to the ip pool or gets nottified immediately?

Reply to
Nicky

There are probably a dozen ways, depending on the device giving out the leases. With many devices, rebooting it will do that.

-Russ.

Reply to
Somebody.

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