Опубликован: 06.08.2012 | Доступ: свободный | Студентов: 1189 / 25 | Оценка: 5.00 / 5.00 | Длительность: 53:41:00
Лекция 18:

Connecting to the Internet

< Лекция 17 || Лекция 18: 12 || Лекция 19 >
Аннотация: The physical connection; Establishing yourself on the Internet; Choosing an Internet Service Provider; Who’s that ISP?; Making the connection.

To implement the reference network shown in the previous chapter, we need to do a lot of things that interface with the outside world. They can take some time, so we should look at them first:

  • What kind of physical connection should we use? We'll consider that in the next section.
  • We may want to register a domain. Many people don't, but I strongly recommend it. Find out about that on page 317.
  • We may also want to register a network. In our example, we have used the network 223.147.37.0. In real life, we can’t choose our own network: we take what is given to us. We’ll look at this on page 318.
  • We need to find an Internet Service Provider. We’ll look at what that entails on page 319.

The physical connection

Just two or three years ago, the way to connect to the outside world was simple: a phone line. Since then, things have changed quite a bit, and you may have quite a choice:

  • Analogue telephone line connections are still the most common way of connecting small networks in most countries, but their bandwidth is limited to about 7 kB/s at best. You can run PPP or SLIP over this kind of line, though nowadays most ISPs support only PPP.
  • ISDN stands for Integrated Systems Digital Network. It's he new, better, washes-whiter telephone system that is replacing POTS (Plain Old Telephone Service) in some countries, notably in Europe. FreeBSD supports ISDN with the isdn4bsd driver. We won't look at ISDN further in this book.
  • Leased lines form the backbone of the Internet. They're invariably more expensive than dialup lines, but they can provide quite high speeds in the USA, a T1 line will give you 1,536 kbps, and in the rest of the world an E1 will give you 2,048 kbps. Leased lines are becoming less interesting, and we won’t look at them in more detail in this book.
  • Cable modems use existing cable TV networks to deliver high speed connection, up to several megabits per second. They use the cable as a broadcast medium, rather like an Ethernet, and suffer from the same load problems: you share the speed with the other users of the cable. There are also some security issues to consider, but if you have a cable service in your area, you'll probably find it superior to telephones. The cable modem is effectively a bridge between the cable and an Ethernet. From the FreeBSD point of view, the cable modem looks like just another Ethernet device.
  • DSL (Digital Subscriber Line) is the telephone companies' reaction to cable modems.
    Until recently, the L stood for Loop, not Line. A loop is the telco term for the pair of wires between the exchange (or Central Office) and the subscriber premises.

    There are a number of variants on DSL: ADSL (Asynchronous Digital Subscriber Line) has different speeds for the uplink and the downlink, while SDSL (Symmetric Digital Subscriber Line) and HDSL (High-speed Digital Subscriber Line) have the same speed in each direction. Speeds and capabilities differ widely from one location to another. By modifying the way they transmit data over normal phone wires, including the use of special modems, ADSL can get speeds of up to 6 Mb/s downstream (towards the end user), and about 640 kbps upstream. HDSL has similar speeds, but the speed is the same in each direction. In contrast to cable modems, you don’t have to share this bandwidth with anybody. Technical considerations limit the loop length to about four miles, so even in big cities you may not be able to get it. Many DSL services are plagued by technical problems. There are a number of different ways to connect to a DSL service, but most of them involve a conversion to Ethernet.

  • In some parts of the world, satellite connections are a viable alternative. These usually use a telephone line for outgoing data and a satellite receiver for incoming data. Pricing varies from very cheap to quite expensive, but if you can’t get cable or DSL, this might be your only choice.

Establishing yourself on the Internet

The first thing you need to decide is the extent of your presence on the Net. There are various possibilities:

  • You could get a dialup service where you use your computer just to connect to the ISP, and perform network functions such as reading mail and news on the ISP's machine (a shell account). It’s lot faster to perform these functions on your own machine, and you have all the software you need to do so, so this option isn’t very desirable. This option is becoming increasingly uncommon.
  • You could perform all the functions on your machine, but using names and addresses assigned to you by the ISP.
  • You could perform all the functions on your machine, using addresses assigned to you by the ISP, but you would use your own domain name.
  • You get your own address space and use your own domain name.

Does it matter? That’s for you to decide. It’s certainly a very good idea to have your own domain name. As time goes on, your email address will become more and more important. If you get a mail address like 4711@flybynight.net, and Flybynight goes broke, or you decide to change to a different ISP, your mail address is gone, and you have to explain that to everybody who might want to contact you. If, on the other hand, your name is Jerry Dunham, and you register a domain dunham.org, you can assign yourself any mail address in that domain.

But how do you go about it? One way would be to pay your ISP to do it for you. You don’t need to do that: it’s easy enough to do yourself on the World-Wide Web. You must be connected to the Internet to perform these steps. This implies that you should first connect using your ISP's domain name, then establish your domain name, and change to that domain.

Which domain name?

We’ll continue to assume that your name is Jerry Dunham. If you live in, say, Austin, Texas, you have a number of domain names you can choose from: dunham.org, dunham.com, dunham.net, or even dunham.tx.us if you want to use the geographical domain.

If you live in, say, Capetown, people will probably suggest that you get the domain dunham.za, the geographical domain for South Africa. The problem with that is that you are limiting yourself to that country. If you move to, say, Holland, you would have to change to dunham.nl—a situation only fractionally better than being bound to an ISP. The same considerations apply to dunham.tx.us, of course.

Your choice of domain name also affects the way you apply. In the following sections, I assume you take my advice and apply for an organizational rather than a geographical domain.

Preparing for registration

Once upon a time, registration was handled by Inter NIC, a professional body. Since then it has been delegated to commercial companies, and the quality of service has suffered correspondingly: they don't even appear to know the technical terms. For example, you may find them referring to a domain name as a "Web Address." Things are still deteriorating at the time of writing: additional companies are being allowed to register domain names, and the field seems to attract a lot of cowboys.

Registering a domain name

The only prerequisites for registering a domain name are:

  • The name must be available, though there are some legal implications that suggest that, though you might be able to register a domain such as microsoft.edu, it maight not be good for you if you do. In fact, microsoft.edu was once registered to the BISPL business school in Hyderabad, India, presumably not in agreement with Microsoft.
  • You must be able to specify two name servers for it—see "Chapter 21" for further details about name servers.

First, check that the name is available:

$ whois duriham.org
No match for " DUNHAM.ORG ".

The Inter NIC Registration Services Host contains ONLY Internet Information
(Networks, ASN's, Domains, and POC's).
Please use the whois server at nic.ddn.mil for MILNET Information.

Next, try to find a reputable registrar. Immediately after the transfer of registrars from Inter NIC, the only company to offer this service was Network Solutions, but now there are many. I do not recommend Network Solutions: they're expensive and incompetent. If, as I recommend, you set up your mail server to refuse mail from servers without reverse mapping, you will not be able to communicate with them, since they do not have reverse DNS on their mail servers, and they use unregistered names for them. Judge for yourself what this says about their technical competence.

One registrar that many FreeBSD people use is Gandi (http://www.gandi.net/), which is slightly associated with the FreeBSD project. So far nobody has found anything negative to say about them. Unlike Network Solutions, their web pages are also relatively simple to understand.

Getting IP addresses

Once upon a time, it was possible to get IP addresses from Inter NIC, but this practice is now restricted to large allocations for ISPs. Instead, get the addresses from your ISP. Routing considerations make it impractical to move IP addresses from one place to another. Ifyou move a long distance, you should expect to change your IP addresses in the same way as you would change your telephone number.

Choosing an Internet Service Provider

In most cases, you will get your connection to the Internet from an Internet Service Provider, or ISP. As the name suggests, an ISP will supply the means for you to connect your system or your local network to the Internet. They will probably also supply other services: most ISPs can’t live on Internet connections alone.

In this chapter we'll look at the things you need to know about ISPs, and how to get the best deal. We’ll concentrate on what is still the most common setup, PPP over dialup line with a V90 modem (56 kbps), which will give you a peak data transfer rate of about 7kB/s.

< Лекция 17 || Лекция 18: 12 || Лекция 19 >
Владимир Шишкин
Владимир Шишкин
Россия, Киров
Олег Страхов
Олег Страхов
Россия