Basic IP Address Questions

A Primal Nut

I'm trying to figure out how IP addresses work but I'm confused. As I understand, you are allocated a different IP Address by your ISP every time you log onto the internet. When I type in "What is my IP address" into a search engine I get a different answer everytime I log onto the internet. Which is fair enough. But if that's the case how can certain websites block your IP address. For example, if you change wikipedia anonymously for malicious purposes they can detect your IP address and then send you a message next time you log on warning about the change you made. They can even block your IP address if you continue to offend. But if your IP address changes every time you log into the internet, how can they block it. This is assuming a normal domestic broadband connection.

Also when I do IP config on my computer I get a range of addresses returned. I understand default gateway is the address used to connect to the Internet, which presumably everyone on that ISP would use. But what about the IP address listed here, which is the same all the time and as I understand it, unaccessible to the outside. Is this the address of the nearest router?

Spear

A Primal Nut wrote: »

I'm trying to figure out how IP addresses work but I'm confused. As I understand, you are allocated a different IP Address by your ISP every time you log onto the internet.

No, not always.

When I type in "What is my IP address" into a search engine I get a different answer everytime I log onto the internet. Which is fair enough. But if that's the case how can certain websites block your IP address. For example, if you change wikipedia anonymously for malicious purposes they can detect your IP address and then send you a message next time you log on warning about the change you made. They can even block your IP address if you continue to offend. But if your IP address changes every time you log into the internet, how can they block it. This is assuming a normal domestic broadband connection.

They don't always change.

Also when I do IP config on my computer I get a range of addresses returned. I understand default gateway is the address used to connect to the Internet, which presumably everyone on that ISP would use. But what about the IP address listed here, which is the same all the time and as I understand it, unaccessible to the outside. Is this the address of the nearest router?

The one that's not changing is your own static internal address, NAT'd to whatever your ISP has given you.

Gavin

You are generally correct when you say that when you connect to the internet you get a different IP address. This technology is called DHCP, Dynamic Host Configuration Protocol.

Most ISPs will use DHCP to give out IP addresses when they recieve a connection. Regarding the actual addresses. Typically what happens is that your router, located at home, has two IP addresses. The first IP address is just for the local network and remains fixed. The second IP address is the one that is recieved, via DHCP, from the ISP. Your pc then connects to the router, and the router connects out onto the Internet via the ISP.

With blacklisting, you are right, it's sometimes based on IP. So Wikipedia for example will blacklist a particular IP if it causes trouble. But then you reconnect and get a new IP that Wikipedia doesn't recognise. What Wikipedia might do in that scenario is to block a range of addresses. Eircom for example has a specific set of IP addresses it is allowed to give out to customers. If Wikipedia sees continuing abuse from different IPs, all within that Eircom set, they might just block all of them.

The other approach they might take is rather simplistic. They could use cookies to identify blacklisted people on new IPs. This will work in simple scenarios, but it's trivial to delete/reject cookies.

seamus

Verb wrote: »

With blacklisting, you are right, it's sometimes based on IP. So Wikipedia for example will blacklist a particular IP if it causes trouble. But then you reconnect and get a new IP that Wikipedia doesn't recognise. What Wikipedia might do in that scenario is to block a range of addresses. Eircom for example has a specific set of IP addresses it is allowed to give out to customers. If Wikipedia sees continuing abuse from different IPs, all within that Eircom set, they might just block all of them.

There were some recent high-profile cases of this where wikipedia blocked all IP addresses belonging to certain U.S. Government departments (political ones, not like the FBI) because they were constantly changing articles to portray their politicians in a better light.

IP addresses aren't necessarily random. As Verb says, an ISP (such as eircom) is allocated a block of sequential IP addresses, such as 194.125.0.0 - 194.125.255.255. I'm not going to explain how that's a sequence of numbers, rest assured, it is.
When you go onto the internet, your modem requests the last IP address that it had. If this address is unavailable (if someone else got it), eircom assigns you a new IP address from their available block, e.g. 194.125.100.25.

So while your IP address may change each time you go on the internet, you will still only have an IP from a set range of IPs, which makes you a little more traceable.

IP address blocking largely works against the small-time irritations and spammers. Anyone who's concerted enough will have access to a large number of IP addresses (through proxy services) from different address ranges, such that they would be impossible to block. These people are are rare enough though and unless there's some financial gain, only the mentally ill ones will continue a campaign against sites like wikipedia.

A Primal Nut

seamus wrote: »

IP addresses aren't necessarily random. As Verb says, an ISP (such as eircom) is allocated a block of sequential IP addresses, such as 194.125.0.0 - 194.125.255.255. I'm not going to explain how that's a sequence of numbers, rest assured, it is.

Don't worry, I understand that bit well. Thanks for the answers - I suppose it means soomeone could be wrongly blocked from a site if they are in a range of addresses with someone else who was being a nuisance to that site.

monkey tennis

A Primal Nut wrote: »

I suppose it means soomeone could be wrongly blocked from a site if they are in a range of addresses with someone else who was being a nuisance to that site.

Happens all the time.