In the last 3 days, I have seen my external IP and noticed that it is changing every day. Why is it so?
While Santosh is correct there is more to it than that. I've been with AT&T for a few years now. My external IP address would stay the same for months, basically until I powered down my dsl modem for some reason. This summer I started hosting a minecraft server for my son and his friends. I leave my modem/router/pc on 24/7 and my external IP address changes about every other day. So ATT analyzed my traffic and decided they didn't like it that I was hosting something on my pc, so they are intentionally making it hard for me.
This is not the first time ATT has done something similar. Last year I was using bittorent to download a new 500mb file once a week. Within a few minutes of starting a torrent my downstream connection would be throttled to about 120kbits/s.
So your isp is f#@%ing with you. If you have another choice switch. I don't the only two games in this town are ATT and comcast. Comcast was also terrible.
If you have a dynamic ip address but need consistant access to your machine you could always use a dynamic name service like http://www.noip.com/
Do note that it will not make your IP address remain the same, it will turn it into a 'fixed' domain.
Most ISPs allocate their range of IP addresses dynamically (using DHCP), and the "lease" is often set to 24 hours, which is why your address changes at that frequency.
If you need to have a fixed address, you can ask your ISP for static address. I they offer this service at all, they will charge you for it.
Alternatively, you can use a Dynamic DNS address service (look it up on Wikipedia). These services associate your actual address (in its numerical form) with a fixed mnemonic address (e.g. //www.makeuseof.com) in real time, so as long as you give out the mnemonic form, your other users will be able to access your server.
Some ISPs change the IP address frequently, others provide it on a long lease but may still change it. Changes are more likely if you turn off your router when not in use. For most users changing IP doesn't matter. If you need a fixed IP the ISP can probably provide one for a small fee and there are other solutions if you do have that requirement.
Generally ISPs use dynamic IP address for home users. Using dynamic IPs allow them to re-utilise the available set of IPs for a large number of users as all the users are not online at all the times. This is why your IP changes every time whenever you create a new connection/everyday.
Recently i created Counter Strike 1.6 Internet Based Server so i need to give my external ip to my friends but if it changes everyday then it is not possible to give them new ip everyday. So how can i get a static external ip?
As mentioned by Rob below, ISPs charge additional fee for a static IP. Contact your ISP for the details.
The explanation given by Santosh is perfect. ISPs may charge you extra for Static IP assignment and are usually available with Business packages which usually has a much higher fee and a SLA commitment. Contact your ISP for further details, as the policy varies from ISP to ISP. Ask them about the business packages and can a Ststic IP be provided with their home package at an extra cost. Otherwise, as standard practice, home users get dynamic IPs.
perhaps You have a dynamic IP address rather than static IP