IP Address Changing Without Router or Computer Restart

[AmbiguousNinja]

Hello, recently my global IP address (the one I can find by simply searching "IP" in google) has been changing even though I have not restarted my router or laptop. This was not occuring for the past year only in the last week or two. My ISP is Bell Canada. I do have a dynamic IP but before it would only change upon restarting my router. I'm curious as to why this is happening because to my (not very extensive knowledge), IP addresses should not change by themselves like they are currently.

I use an early 2011 Macbook Pro running OS 10.8 Mountain Lion. The IP changes seem to occur anywhere around 1 to 5 days and every time it did change I restarted my router to see if the IP would change (and it did). After the third change, I messed around with settings on my router and laptop which I have since reverted except for a DNS cache flush that I did yesterday. This morning when I checked my IP I found that it had changed from the night before.

I'm not sure if it helps but starting from around 1-3 days ago, my ping has doubled to about 50ms but my dl and ul speeds remain more or less the same (in fact I think my DL speeds went up a little). Could this have anything to do with my ISP upgrading or moving servers and would this force my IP address to change? For the first week and a half of my IP changing itself my ping and speeds were the same as usual.

One last thing, my ping now (~50ms) is the same as it was about 7 months back when my internet speeds were fairly slow as well. After getting a bandwidth cap my speeds went up and my ping fell to ~22ms. That hasn't changed at all in the last 7 months.

Sorry for the wall of text and thanks in advance for any answers!

[Geek-9pm]

Welcome to CH. The forum answers any reasonable question.
Some, not all, ISP companies will change the internet IP from time to time. It is often done to balance the traffic load on the ISP routers. For example, you and a number of other users may be on one of the IPs available to the company in your area. Let's say the number got up to 61 and maybe  the limit for that switch is 64. At the same time another switch has 11 people on it. So then, the ISP will reset the connection and give you the IP with the lessor traffic. On other days it might not be needed. Or they will move other users  instead of you.
Does that answer your question?

To clarify, the OP is talking about the address on the internet, the WAN address.
I am sure he does not mean the local address on the LAN

Typically the lease on an internet address will expire in 24 hours, but this is not a hard rule. Of course web sites should have fixed IPs that stay the same. Bet even they must sometimes change due to unseen issues. The DNS system takes care of this. Or it should.
hard rule.

[AmbiguousNinja]

Thanks, that clears up a lot! I'm just curious to know why this has only started occurring frequently in the past two weeks. The only other thing I'm not clear on is whether or not my WAN address can change without restarting my router or laptop connection, previously when I wanted to change my address I would restart my router as I thought that was the only way.

Nevertheless, thanks for the quick reply and I'll be sure to help other people with areas that I'm more familiar in, thank you!

[Geek-9pm]

Each ISP is different. And they can change when needed. FYI If you are an enterprise business and always having the same  address is critical, you can pay more money to insure the ISP never changes it.

Also, we here are talking about IPv4. But is using IPv6 there should not be a reason to ever change. (One source says in IPv6 the lower 64 bits are static.)
Hope this is of some help.