h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: IP Network Addresses - A12179216
Author: Caveman, Evil Unix Sysadmin, betting shop operative, and SuDoku addict (Its an odd mix, but someone has to do it) - U30753

Various articles on TCP/IP networking exist, but as yet none actually describe why IP addresses work as they do, and instead say 'Set your IP address to blah, your netmask to blah, etc.'
This is an initial attempt to clear this up once and for all.
TODO:
Add links to suitable articles (to explain terms like 'Binary', 'Network', 'Interface' etc.
De-Waffle-ize the last paragraph
Rule 3 is too complicated, and needs more basic rules added beforehand.
Explain why quoting IP addresses with leading zeros is a Bad Thing(TM)
...loads more.

Must read.

OK, here goes.

Firstly, put full-stops on your footnotes.

>>Whether your network runs on ethernet, token rings, ARCnet, carrier-pigeon, serial lines, or wet-peices-of-string,<<

You may want to explain what some of these are in footnotes.

>>Every network interface in an IP network has an address ('IP Address'). If a machine on the network (a 'host') has more than one interface, it will have more than one IP address. <<

If I didn't know what you were talking about, I might not know what you were talking about. Meaning, you might want to include brief paragraph explaining what a network is. Then, the casual reader will know that a machine with more than one interface is host to an intranet. (Which is what you're talking about, right? )

>>No two network interfaces that can possibly talk to each other can have the same IP Address<<

lacks a full-stop after it. Also, maybe rephrase: no two network interfaces can have the same IP Address and communicate with each other. OR No two network interfaces can communicate with each other if they have the same IP address. OR even more simply: No two network interfaces can have the same IP address.

>>This network mask tells the network how many bits of the 32-bit IP address are 'network bits' and how many are 'host bits'.<<

You will explain the difference between network bits and host bits? I don't see that you do, and I find it a little puzzling. I've never heard of these before. Therefore, the entire following paragraph makes no sense to me, and I understand the basic concept of ASCII. The charts clarify - but not definitely.



>>Rule number 3:<<
Awesome! I'm finally understanding this.

>>When it realises that the BBC's web server is not on it's own local network, <<
- its, not it's.


Great entry. Just the mask part is still a little confusing.
One question I had about the charts: If the first part of the mask is just in ones, how do you translate it into the 'network bit' underneath, with its zeros and ones?

...also, is there any configuring to the gateway that the reader might want to know about?

And how does the configurer then choose an IP address - or know what to set it to?

Thanks for the replies. I've been away for a few days. I shall integrate the points raised into the article in due course (but probably not today).

In answer to some of the points:
Explaining media types: There are probably a number of articles around that I can link to.

I obviously need to explain 'interfaces' far better.

As to the application of netmask to IP address to get network bits and host bits, the operation is a bitwise AND to get the network bits, and bit wise AND with NOT netmask to get the host bits. All the netmask really represents is a boundary. I shall go into deeper detail.

The reference to carrier pigeons is going to point off-site to www.blug.linux.no/rfc1149

I'm staying subscribed. Yell when you're ready.

You still around?

Oh please be! I *liked* this entry!

Yup,
unfortunately had about zero time, with way too much work.

Once the evening racing season finishes, at the end of the month, I'll have some more time.

In case anyone is still listening, the evening racing season didn't finish. It is now year-round. This means I have had no time at all. Annoying, but if anyone wants to take over and run with this article, please be my guest.

Jim

I might get back to this soon, having been made redundant, and now working full-time for the betting industry, I actually do have a few hours to do stuff like this (when I'm not shooting brigands and their spawn on Puzzle Pirates). Quite how I update it for the wonderful world of IPv6 (a world in which I now have a personal allocation of addresses numbering something like a '3' with 25 '0's after it) I don't know.