PDA

View Full Version : What is/Where is 192.168.000.001/2/3?


chuckh2d
May 9, 2005, 11:24 PM
Sorry to be an idiot about this if it's a web-address 101 thing, but I thought IP addresses were supposed to be unique. Yet this particular series of IPs turns up everywhere and I can’t figure out why... Is it a generic setting for any iMac?

I’d been having a kernel panic attack earlier today (OS X forum “Tiger v. 10.2.8/ Norton Utilities kernel panic”) and at the end of the panic alert window (“You need to restart your computer...”) there appeared these two numbers: an IP address 192.168.000.003 and a memory location[?] 00:33:65:B8:2A:3A Presumably they’re both referring to my computer, a dual G4/500, although its boot drive is the 20G drive I took out of my late iMac Indigo after its motherboard died.

I’ve pinged the IP from a PC on the same network and gotten a normal response. 4 32-byte packets returned in milliseconds... again it looks as if it’s my Mac, or perhaps it’s my NetGear wireless router, but it also belongs to a zillion other people as well... (Google “192.168.0.3” and see). What does it all mean? Is this a good thing?

Can anyone enlighten me? Thanks

mkrishnan
May 9, 2005, 11:36 PM
There are a few sort of "special" IP addresses. I don't know them all, but:

127.0.0.1 is a loopback address -- it's supposed to refer to your computer.

192.168.x.x and 10.1.x.x are used by routers / switches. When you have a switch, all the computers on the downstream side of the switch (e.g. your side) share the same upstream (e.g. the cable company's side) IP address. The switch's job is to allow connections to different places by different machines within the local network to work simultaneously. Whatever your IP address is on the upstream side, the switch matches packets to a particular downstream computer by a history table of sorts.

So, if computers that are upstream (i.e. on the internet) want to communicate with computers that are downstream, they can all use the same single IP address that the network assigned the switch. But if computers inside your network want to communicate, this won't work, because it will appear to them like they are trying to communicate with themselves -- they need to send to an IP address different from the one they themselves have leased.

As a result, in the downstream network, computers have IP addresses of 192.168.x.x, which are leased from the router, but in the upstream network, they all have the address the router leases from the service provider. Does this make sense at all? Typically, also, 192.168.0.1 is the router / switch itself. The two sets are basically equivalent (192.... and 10....) but routers can usually be set to use either one.

John Jacob
May 9, 2005, 11:37 PM
Hi,

I'm no expert, but here's what I know...

Some classes of IP addresses are designated as IP addresses for private networks. These IP addresses can be used internally (by a company or institution) but cannot be accessed from the internet. When a computer with a private IP accesses a web page or some other data on the internet, it's IP address must be tranlated to a public IP address by a firewall or router with NAT (network address translation) software. The same firewall will change the destination IP address of the packets returned from the web server and forward them back to the computer with the private IP address.

The classes of IP addresses designated as private are :
10.*.*.* (a class A network)
172.17.*.* to 172.31.*.* (a class B network)
192.168.*.* (a class C network)

Hope that makes sense. I'm sure some MacRumors expert will come along soon with a more lucid explanation.

plinden
May 9, 2005, 11:50 PM
I only have a fuzzy understanding of this so can't give you a full technical explanation.

There are only a limited number of IP addresses in the world. Your ISP will have a block of these addresses to assign to users to provide them with access to the internet. The IP address of your home network would look something like 67.115.x.x (for sbcglobal.net). But since you have a router, it handles all requests from your computers to the outside world, and knows to which computer on your network to route responses.

Since your network is isolated from the main internet, it can use pretty much any IP addresses at all to identify the computers internally (I think, but I'm not sure, that certain addresses are reserved for use internally in networks). For instance, my employers use 10.16.x.x to identify computers internally, but those computers that are outside the firewall (e.g webservers) will have totally different extenal IP addresses to their internal ones. Only if you are on my employers network would the 10.16.x.x addresses be accessible to you.

192.168.x.x happens to be the most common internal network addresses used. Netgear uses 192.168.0.x and Linksys uses 192.168.1.x. These tend to be assigned by the router sequentially - so the router will have address 192.168.0.0, and any other computer added the network will take the next address available. So if you ping 192.168.0.3 and get a response, it just means one of the computers on your internal network has been assigned that IP address and is responding to your ping. I'm pretty sure that 192.168.0.3 isn't an IP address of a computer on the external network.

mkrishnan
May 9, 2005, 11:55 PM
LOL, hopefully between our three confusing explanations.... ;) :eek: :D

John, what do class A/B/C networks mean? I haven't heard this distinction, or I think, seen a Class B. And the AEBS will let you switch between 192.x and 10.x without any apparent real impact on anything...but is there actually a hidden significant impact of doing it?

nrd
May 9, 2005, 11:55 PM
IANA, the organization that controls the protocols behind the internet has RFC-3330, which outlines special use IPv4 addresses.

http://www.rfc-editor.org/rfc/rfc3330.txt

If you really want to know about those addresses, check it out.

Oh and if anyone ever asks you what your IP address is, tell them it's 127.0.0.1 :D

nrd
May 9, 2005, 11:58 PM
LOL, hopefully between our three confusing explanations.... ;) :eek: :D

John, what do class A/B/C networks mean? I haven't heard this distinction, or I think, seen a Class B. And the AEBS will let you switch between 192.x and 10.x without any apparent real impact on anything...but is there actually a hidden significant impact of doing it?

http://www.iana.org/assignments/ipv4-address-space

IANA allocates that first octet (A) to one organization or another. That organization now manages that portion of the IP addressing range. They can then sublet, so to speak, the second octet (B) to another organization or entity.

Sun Baked
May 10, 2005, 12:04 AM
The local networks are a lot like a PBX phone system, you got one number to call in on an a whole lot of people inside using that number -- with the router being the main number.

The 192.xx... number is a lot like your personal extension.

With those numbers you can get anybody inside the phone system, hand that extension number alone to somebody in the outside world -- and they have no way to call you.

You can statically give the 192.xx... number to a specific port on the router.

So with the main router IP address and the port number they can lay their hands on you.

The extensions are your private numbers that work well within the phone system (the private network) and the router's IP address is the public number they have to call in on (the public network).

---

Somebody can probably be more clear.

But the phone systems are generally hell and complex enough for people to get lost if they don't know exactly where you are.

mkrishnan
May 10, 2005, 12:13 AM
http://www.iana.org/assignments/ipv4-address-space

IANA allocates that first octet (A) to one organization or another. That organization now manages that portion of the IP addressing range. They can then sublet, so to speak, the second octet (B) to another organization or entity.

Actually, I don't think this is what I was talking about. The previous poster stated that the 192.xxx and 10.xxx downstream addressing schemes fell into different "classes" -- but that's not what the .txt file you linked implied. It doesn't seem to make any meaningful distinction between a local network that operates on one set of IPs reserved for LANs vs. the other ones. I understand the difference between the top level octet and the second level octet. But thanks for the very informative links!

John Jacob
May 10, 2005, 12:20 AM
LOL, hopefully between our three confusing explanations.... ;) :eek: :D

John, what do class A/B/C networks mean? I haven't heard this distinction, or I think, seen a Class B. And the AEBS will let you switch between 192.x and 10.x without any apparent real impact on anything...but is there actually a hidden significant impact of doing it?

A class A network is a network (actually a subnet) with 16 million addresses (2^24). A class B network has 65536 address (2^16). And a class C network has only 256 addresses (2^8).

There are 126 class A networks from 1.*.*.* to 126.*.*.* (I think 0.* is reserved for broadcast). There are 16384 class B networks from 128.* to 191.* (iirc, 127 is reserved for loopback). There are 2^21 class C networks from 192.* to 223.*. There are also class D and E networks.

There is one network from each of the classes A, B and C that is designated for private networks.

And to answer your question, there shouldn't be any impact whether you use 10.x or 192.x with your AEBS - unless you have more than 256 devices in your home network - in which case you will have to use 10.x (I don't even know if an AEBS will support more than 256 devices).

Some links on internet addressing - How Stuff Works (http://computer.howstuffworks.com/question549.htm) and FAQS.org (http://www.faqs.org/docs/linux_network/x-087-2-issues.ip-addresses.html)

[Edited to add links]

chuckh2d
May 10, 2005, 12:22 AM
Many thanks John and Mohan--

This is getting clearer...or at least I'm not as worried anymore... Good to see it's sparked some debate in any event!

I see that e-mails sent to myself have three "received from" lines: (1) the originating IP that seems to be my unique IP (209.239.x.x), (2) Comcast's shcrmcc11 (whatever that is --at 204.127.x.x), and (3) the 192.168.0.3 address that we've been talking about. (All hail Eudora's BLAH BLAH BLAH button)

I think I understand now why my computer refers to itself by its name within my own "downstream" network (as 192.168.000.003) in the kernel panic notice instead of using the unique number or the PowerPC number that reported itself to Apple when I registered Tiger... But since this number appears in the "received from" information no matter which computer I send the e-mail from does this mean that both my PC on the network AND my G4/dual 500 are calling themselves by the same IP number aw geez my head hurts.

cheers,

C.

nrd
May 10, 2005, 12:26 AM
Actually, I don't think this is what I was talking about. The previous poster stated that the 192.xxx and 10.xxx downstream addressing schemes fell into different "classes" -- but that's not what the .txt file you linked implied. It doesn't seem to make any meaningful distinction between a local network that operates on one set of IPs reserved for LANs vs. the other ones. I understand the difference between the top level octet and the second level octet. But thanks for the very informative links!

That listing I linked to is for the first octet, or a class A address. Hypothetical: General Electrics' Class A addresses are 3.x.x.x. They allow Lockheed Martin use of a set of Class B addresses, so Lockheed gets 3.26.x.x to use. Lockheed could then assign 3.26.100.x (Class C) for the computers in one region or another. The link before that one has information on the special classes of IP addresses for subnets like the 192.168.x.x's

The PBX analogy is a good one - You can have multiple 192.168.x.x subnets hooked up to 500 computers behind one cable modem. Inside the subnet there are five hundred machines, but from the rest of the internet, there's only one machine via one IP address. The router handles Network Address Translation (NAT), which allows machines on the internet to connect to one of those 500 machines through that one IP address. NAT also allows for multiple 192.168.x.x networks all over be able to talk to each other.

I hope this helps, and I hope this is clear. It's too late for me and I should be working on a paper.