Static IP'ing

[WanderingKnight]

I'll have to damn my lack of knowledge in networking for this...

I recently moved to my dad's, and we have a router for three PCs. Originally everything was setup correctly, the router was set to static IP from one time I had done it long long ago in order to set NAT forwarding correctly on my dad's PC. We needed to move a few things around to get the cables right, but when we finally got all set up and going, I find with surprise that none of the machines could solve DNS anymore. I was puzzled as to the reason, so the only thing it occurred to me was to reboot the router to factory standards (and, like an idiot, I forgot to save a screenshot with the static IP configuration) to see if there was anything wrong with it (my dad actually smashed it against the wall quite heavily because he was trying to get it to stick to a couple of screws he set on the wall).

So sure, when I rebooted the router to factory standards, everything was going smoothly--DNS resolved perfectly. So I said, I have to forward the ports again to set the NAT correctly--but I need to set the router to forward to a static IP, I said. And that's where my woes began.

Here's a picture of the static IP setup I was trying to use:



If I understand it right:

Internet IP address: Public IP address, obtainable from sites like whatismyip.com.
ISP Gateway Address: Now, this is a value I didn't understand too much. I cannot get it from my PC, and when I try saving the values without entering nothing here the router spits out an error. So, googling around I got to the conclusion that I had to use my router's IP address within my network. I really can't remember how I set it up last time.
And the DNS servers.

For some reason, the DNS servers I get assigned through DHCP are not the same as the ones provided by my ISP (I called them asking about this, since at some point I suspected there was some kind of issue on their side or the sudden breakage of the network I experienced earlier wouldn't have happened).

So, with that setup, why is it that I can't resolve DNS? I already set the Windows machine to get a static internal IP address (192.168.1.xxx) and use the DNS servers stated in the router. My Linux box is also set to an internal IP address. Why can't it resolve?

Or am I doing something patently wrong? I don't remember going through so many hoops.

[Sephi]

Seeing the screencap. It looks a lot like my Sweex interface. Not sure if it is. Or if this info will do you any good. But if it is a Sweex. Have you tried the Wizard? let it do it automatically. And see what values for the ISP gataway it gives?

And again if it is a Sweex. For my router forwarding ports for application is done in the "Forwarding>special AP/Virtual Server" And assigning a static ip is controlled by security>Mac controll. It will assign a IP according to the Mac address.

If it isn't perhaps it's best to google the manual for your router to see how it's done.

[jedinat]

Your router shouldn't be set as static; it should be "Automatic - DHCP" (what mine says)

You set the DHCP server settings as static to use static IPs on your LAN.

...or you are doing something different and don't want your ISP to assign you your IP, in which case ignore me because I really don't know all that much about networking.

[cyberbeing]

Your problem is ISP Gateway Address ≠ Router Address yet you have them as the same thing. The ISP Gateway Address is an external address from your ISP that assigns an IP to your machine and allows you to connect to the internet.

If your paying for a Static IP then call your ISP up and ask them what the Gateway Address is.

If you are forcing a static on a DCHP connection then you'll want to connect via DCHP, copy down the Gateway Address it uses, and use that when you set it back to Static IP.

Edit: I guess I should ask, is your internet connection connected directly to this router (lets call it router A) or is another router (lets call it router B) hosting the connection and you're trying to connect router A to router B and be able to access the internet? If that is the case the info I posted above is useless.

[TheFluff]

It may be helpful to try to understand what a gateway is.

Technically all IP addresses should be unique, with one address per computer (or per NIC). When the internet started to explode in size in the early 90's it was quickly realized that IPv4 didn't have enough addressing space, so work was started on IPv6. Meanwhile, someone also came up with a solution: NAT (Network Address Translation). With NAT, you can "hide" a whole subnet behind a single IP address, so that pretty much all home-user computers can use an address in the 192.168.0.xxx range without conflicting with each other. However, for NAT (and indeed actually most IP routing) to work you need to tell the NAT'ed computers which address acts as a "gateway" out of the local subnet. For your computers behind the router, the gateway is the router's local IP address; this tells them that when trying to connect to an address that isn't locally reachable (not masked by the subnet mask) they should just throw it to the gateway. For the router, you need to tell it either to get its IP address and other settings assigned to it automatically by DHCP from your ISP, or tell it what its internet IP address is supposed to be, what the subnet mask is (and hence what addresses are immediately accessible) and what its gateway is (i.e. where it should send requests to addresses that aren't in its own subnet). In the latter case (static IP) you should have received all of the necessary data from your ISP, so just call them up and ask for it.

TL;DR: do what cyberbeing said

[SeijiSensei]

NAT isn't the reason why gateways exist. Gateways are simply routers that interconnect between networks. Gateways can perform network address translation, but more often they simply interconnect untranslated networks. (All the routers upstream from you are usually gateways that don't use NAT.)

When you send a request using IP, the first thing that determines how it's routed is the destination IP address. If that address is in the same subnet as you (e.g., 192.168.1.1 and 192.168.1.2 are usually in the same subnet), the packets are simply broadcast over the network and the appropriate destination machine accepts them. If the packets are destined for a network outside your local subnet, there must be a router listening on the local network with rules determining where the packets go next. That's the "default gateway" that your wifi router is talking about.

Usually the default gateway will be assigned to your externally-facing device with DHCP along with its IP address. Most of the time that gateway will have an address nearly identical to the external device's IP address but with a different final octet. For instance, if my ISP assigned 10.10.10.37 to my external router, it's probably the case that the default gateway will be at 10.10.10.1 or sometimes 10.10.10.254. In either case the gateway's external address needs to be in the same subnet as the upstream router with which it communicates.

If you've been assigned a static external IP, you'll need to ask the ISP what the default gateway is (though they should have told you when they set up your account). If you want, try using an address identical to the router's external address except ending in .1 (or .254). That might avoid a phone call to customer support.

If your ISP cuts up its network allocation into smaller or larger blocks, it's a lot harder to guess what the gateway might be. If your "netmask" is something other than 255.255.255.0, the technique I just described won't work. In the early days of the Internet everyone was allocated address blocks that generally ended on octet boundaries. The global demand for address space has made that wasteful technique obsolete.* Address blocks are now assigned "classlessly" making it much harder to guess what the appropriate gateway address might be.

IPv6 will make a lot of this much easier since addresses will use 64 bits rather than the current 32 bits used on IPv4 networks today. Quoting from Wikipedia,

"The very large IPv6 address space supports 2^128 (about 3.4×10^38) addresses, or approximately 5×10^28 (roughly 2^95) addresses for each of the roughly 6.5 billion (6.5×10^9) people alive today.[1] In a different perspective, this is 2^52 addresses for every observable star in the known universe[2] – more than ten billion billion billion times as many addresses as IPv4 supported."

That's probably enough addresses to keep the Internet running throughout our lifetimes and for decades beyond. Most operating systems and networking devices now include IPv6 support, but its deployment has been slow. Partly that's a result of the widespread use of NAT which enables large networks of machines to consume but one or a few external IPs. Without NAT we would have run out of IPv4 addresses long ago. In the IPv6 future, every electrical or electronic device could have a publicly visible address, so if you needed to turn on your porch light while at work, you could send a command to the switch for that light directly. We're a long way from that, but it's not that far-fetched as a model for the future.

__________
*Some large American corporations like General Electric were allocated entire "class-A" blocks when the Internet was still in its infancy. GE, for instance, controls the entire 3.0.0.0/8 block, which comprises nearly 17 million individual addresses.

[WanderingKnight]

Okay, somehow I'm an idiot and I didn't open the port correctly the first time I tried opening before rebooting the router. I'm guessing I must have been in a hurry and clicked "Undo" in the router configuration tool or something like that.

Meh, things I get for not understanding networking :/