Connecting to the Internet In this chapter: connection on the Internet Ser vice Provider connection In this chapter: connection on the Internet Ser vice Provider connection To implement
Trang 1Connecting to the
Internet
In this chapter:
connection
on the Internet
Ser vice Provider
connection
In this chapter:
connection
on the Internet
Ser vice Provider
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
Trang 2best 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 the 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 a 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) hav e 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 hav e 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
Trang 3317 Chapter 18: Connecting to the Internet
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 a 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 like4711@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 domaindunham.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,
Te xas, you have a number of domain names you can choose from: dunham.org,
dunham.com,dunham.net, or evendunham.tx.usif 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 todunham.nl—a situation only fractionally better than being bound to an ISP The same considerations apply todunham.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
Trang 4Preparing for registration
Once upon a time, registration was handled by InterNIC, 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 might 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 dunham.org
No match for "DUNHAM.ORG".
The InterNIC 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 InterNIC, 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 InterNIC, 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 If you move a long distance, you should expect to change your IP addresses in the same way as you would change your telephone number
Trang 5319 Chapter 18: Connecting to the Internet
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 liv e 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 a dialup line with a V.90 modem (56 kbps), which will give you a peak data transfer rate of about
7 kB/s
Who’s that ISP?
As the Internet, and in particular the number of dialup connections, explodes, a large number of people have had the idea to become involved In the early days of public Internet access, many ISPs were small companies run by very technical people who have seen a market opportunity and have grabbed it Other ISPs were small companies run by not-so technical people who have jumped on the bandwagon Still other ISPs are run by large companies, in particular the cable TV companies and the telephone companies Which is for you? How can you tell to which category an ISP belongs? Do you care?
You should care, of course Let’s consider what you want from an ISP, and what the ISP
wants You want a low-cost, high-reliability, high speed connection to the Internet You may also want technical advice and value-added services such as DNS (see Chapter 21) and web pages
The main priority of a small ISP (or any other ISP, for that matter) is to get a good night’s sleep Next, he wants to ensure the minimum number of nuisance customers After that,
he wants to ensure that he doesn’t go out of business Only then is he interested in the
same things that you are
In the last few years, a large number of ISPs have gone out of business, and many more have merged with other companies In particular, large companies frequently bought out small techie ISPs and then ran them into the ground with their incompetence For a humorous view of this phenomenon, see the ‘‘User Friendly’’ cartoon series starting at
http://ars.userfriendly.org/cartoons/?id=19980824.
Questions to ask an ISP
So how do you choose an ISP? Don’t forget the value of word-of-mouth—it’s the most common way to find an ISP If you know somebody very technical, preferably a FreeBSD user, who is already connected, ask him—he’ll certainly be able to tell you about his ISP Otherwise, a lot depends on your level of technical understanding It’s easy to know more about the technical aspects of the Internet than your ISP, but it doesn’t often help getting good service Here are a few questions to ask any prospective ISP:
Trang 6What kind of connections do you provide?
See the discussion on page 315.
How do you charge? By volume, by connect time, or flat rate?
Once most ISPs charged by connect time: you paid whether you transfer data or not This made it unattractive to an ISP to provide good performance, since that would have meant that you could finish your session more quickly Now adays, flat rates are becoming more popular: you pay the same no matter how much you use the service The disadvantage of the flat rate is that there is no incentive to disconnect, so you might find it difficult to establish connections.
When comparing connect time and volume rates, expect an average data transfer rate of about 600 bytes per second for most connections via a 56 kbps modem You’ll get up to 7
kB per second with traffic-intensive operations like file downloading, but normally, you’ll be doing other things as well, and your data rate over the session is more likely to be 600 bytes per second if you’re reasonably active, and significantly less if not Faster lines typically don’t charge by connect time: in particular, DSL lines are permanently connected and thus charge by data volume or at a flat rate.
Another alternative that is again becoming more popular is a ‘‘download limit.’’ Your flat monthly fee allows you to download up to a certain amount of data, after which additional data costs money This may seem worse than a flat rate, but it does tend to keep people from abusing the service.
Do you have a cheaper charge for data from your own network?
Many ISPs maintain web proxy caches, ftp archives and network news If they charge by volume, some will give you free access to their own net Don’t overestimate the value of this free data.
What speed connections do you offer?
ADSL connections have two different rates, a faster one for downloads and a slower one for the uplink That’s fine if you’re planning to use the system as a client If you intend to run servers on your system, things can look very different.
If you are using a modem connection, they should be the fastest, of course, which are currently 56 kbps.
What uplink connections do you have?
The purpose of this question is twofold: first, see if he understands the question An uplink connection is the connection that the ISP has to the rest of the Internet If it’s inadequate, your connection to the Internet will also be inadequate To judge whether the link is fast enough, you also need to know how many people are connected at any one time See the question about dialup modems below.
How many hops are there to the backbone?
Some ISPs are a long way from the Internet backbone This can be a disadvantage, but it doesn’t hav e to be If you’re connected to an ISP with T3 all the way to the backbone, you’re better off than somebody connected directly to the backbone by an ISDN Basic Rate connection All other things being equal, though, the smaller the number of hops, the better.
Trang 7321 Chapter 18: Connecting to the Internet
How many dialup modems do you have?
This question has two points to make as well On the one hand, the total bandwidth of these modems should not exceed the uplink bandwidth by too much—let’s say it shouldn’t be more than double the uplink bandwidth On the other hand, you want to be able to get a free line when you dial in Nothing is more frustrating than having to try dozens of times before you can get a connection This phenomenon also causes people not to disconnect when they’re finished, especially if there is no hourly rate This makes the problem even worse.
Of course, the problem depends on the number of subscribers, so ask the next question too.
How many subscribers do you have? What is the average time they connect per week?
Apart from the obvious information, check whether they keep this kind of statistics They’re important for growth.
What’s your up-time record? Do you keep availability statistics? What are they?
ISPs are always nervous to publish their statistics They’re never as good as I would like.
But if they publish them, you can assume that that fact alone makes them better than their competitors.
What kind of hardware and software are you running?
This question will sort out the good techie ISPs from the wannabes The real answers aren’t quite as important as the way they explain it Nevertheless, consider that you’ll be better off with an ISP who also runs FreeBSD or BSD/OS 1 Only small ISPs can afford to use UNIX machines (including FreeBSD) as routers; the larger ones will use dedicated routers.
Next, in my personal opinion, come other UNIX systems (in decreasing order of preference, Solaris 2.X, Linux and IRIX), and finally, a long way behind, Windows NT If you’re looking for technical support as well, you’ll be a lot better off with an ISP who uses FreeBSD or BSD/OS You’ll also be something special to them: most ISPs hate trying to solve problems for typical Windows users.
How many name servers do you run?
The answer should be at least 2 You’ll probably be accessing them for your non-local name server information, because that will be faster than sending requests throughout the Internet.
Can you supply primary or secondary DNS for me? How much does it cost?
I strongly recommend using your own domain name for mail That way, if your ISP folds,
or you have some other reason for wanting to change, you don’t need to change your mail
ID To do this, you need to have the information available from a name server 24 hours per day DNS can generate a lot of traffic, and unless you’re connected to the network 100% of the time, mail to you can get lost if a system can’t find your DNS information Even if you are connected 100% of the time, it’s a good idea to have a backup DNS on the other side of the link Remember, though, that it doesn’t hav e to be your ISP Some ISPs supply free secondaries to anybody who asks for them, and you might have friends who will also do it for you.
The ISP may also offer to perform the domain registration formalities for you—for a fee.
1 BSD/OS is a commercial operating system closely related to FreeBSD If you have a few thousand dollars to
spare, you may even find it better than FreeBSD Check out http://www.wrs.com/ for further details.
Trang 8You can just as easily do this yourself: see page 318 for more details Check the fee, though: in some countries, the ISP may get a discount for the domain registration fees If it’s big enough, registering via the ISP may possibly be cheaper than doing it yourself.
Can you route a class C network for me? What does it cost?
If you’re connecting a local area network to the Internet, routing information must be propagated to the Net ISPs frequently consider this usage to be ‘‘commercial,’’ and may jack up the prices considerably as a result.
Alternatives to a full class C network are a group of static addresses (say, 8 or 16) out of the ISP’s own assigned network addresses There’s no particular problem with taking this route.
If you change ISPs, you’ll have to change addresses, but as long as you have your own domain name, that shouldn’t be a problem.
Another possibility might be to use IP aliasing See page 393 for more details.
Can you supply me with a static address? How much does it cost?
It’s highly desirable to have static addresses See page 346 for more details Unfortunately, many ISPs use static IPs to distinguish links for commercial use from those for home use, and may charge significantly more for a static address.
Do you give complete access to the Internet, or do you block some ports?
This is a complicated question Many ISPs block services like smtp (mail) or http (web servers) If they do, you can’t run a mail or web server on your own machines In the case
of mail, this is seldom a problem: they will provide you with their own mail server through which you must relay your mail This also allows the ISP to limit spam, which might otherwise come from any system within the network.
For http, the situation is different Usually ISPs charge money for supplying access to their own web servers On the other hand, this arrangement can provide much faster web access, especially if you are connected by a slow link, and you may also save volume charges Ultimately it’s a choice you need to make.
Do you have complete reverse DNS?
In previous editions of this book, I didn’t ask this question: it seemed impossible that any ISP would answer ‘‘no.’’ Unfortunately, times have changed, and a number of ISPs not only don’t supply DNS, they seem to think it unnecessary Don’t hav e anything to do with them: firstly, it shows complete incompetence, and secondly it will cause trouble for you accessing
a number of sites, including sending mail to the FreeBSD mailing lists.
Trang 9323 Chapter 18: Connecting to the Internet
Making the connection
After calling a few ISPs, you should be able to make a decision based on their replies to these questions The next step is to gather the information needed to connect Use Table 18-1 to collect the information you need See Chapter 20 for information about authentication, user name and password
Table 18-1: Information for ISP setup
Information Fill in specific value
IP address of your end of the link
IP address of the other end of the link
Kind of authentication (CHAP, PAP,
login)
User or system name
Password or key
Primary Name Server name
Primary Name Server IP address
Secondary Name Server name
Secondary Name Server IP address
Pop (Mail) Server Name
News Server Name