are internet service providers addresses fixed?

Answer 1

If you have an adsl or cable connection the ip your provider gives you is fixed. If you use a dial-up connection it is variable.

Answer 2

I assume you mean the IP address you get when you connect to the Internet.

Cable and Broadband services provide you with a "Static" IP address - an address that does not change. This is because they can afford to. Each connection is sent through its own wire to your ISP and so you are always connected to the Internet for as long as your modem is working and with on. This is a good benefit of customers, and helps the ISP too, who can change the speed of the connection by changing only the settings for your IP address.

If you use Dial-up (a telephone line and a modem), you share the connection with other people. Your ISP has a range of phone lines, and when you connect to the Internet you are given the next phone line in the queue. This gives you a different IP address each time, or a "Dynamic" address.

There are good and bad points about which to use, but a dynamic address is more secure as it changes each time you connect. Any hackers who lock on to your computer will have to start from scratch next time you connect. However, it's easier to manage and support from the ISP's point of view to use a static address.

With a flood of firewall and anti-spyware programs on the market, many of them free, you should still protect your computer whatever your connection type.

Answer 3

Most broadband connections are in fact dynamic too, but as folk tend to keep connected they can be treated as static... and even with broadband (at least through the phone lines--not sure about cable) theres a 'contention ratio', which means you do share the connection with other users. This is normally 50:1 for home users, whilst businesses get a 20:1 ratio (at a higher cost of course).
An ISP will have a pool of addresses available for leasing out to their customers, irrespective of how those customers connect, but the ISPs addresses (web servers, DHCP servers, DNS servers) will all have static addresses, if these were dynamic there'd be a lot of problems connecting when they changed.

Answer 4

If you are using dial-up then no, IP addresses are not fixed.
If you are using broadband, it depends. Some ISP will give a fixed address for free, some will give a fixed address for a small monthly fee added on and some refuse to give fixed addresses. It is something to keep in mind when shopping for a broadband provider.
Another thing to consider is that some ISP's will block certain ports (80/443 for web, 25 for e-mail) to prevent you from running any servers over their network.