- KnowledgeShare - White Papers
The arrival of low cost broadband technologies in general
and DSL (Digital Subscriber Line)
in particular has greatly increased the number of computer hosts that
are permanently connected to the Internet. This has increased concerns
on the part of DSL service providers about security. Computers connected
to the Internet via DSL do so through an Ethernet link. As such, plain
TCP/IP has been used, with no additional protocols. Modem dial-up connection,
on the other hand, use PPP (Point to Point Protocol) which provides secure
login, and traffic metering among other advanced features. PPPoE (PPP
over Ethernet) was designed to bring the security and metering benefits
of PPP to Ethernet connections such as DSL.
We are presenting this information in a Q&A (Questions
and Answers) format that we hope will be useful. Our knowledge of this
subject relates to Internet connectivity in general, and stems from our
own TCP/IP routing technology. We welcome feedback and comments from any
readers on the usefulness or content.
We are providing the best information available to us as
of the date of this writing and intend to update it at frequent intervals
as things change and/or more information becomes available. However we
intend this Q&A as a guide only and recommend that users obtain specific
information to determine applicability to their specific requirements.
(This is another way of saying that we can't be held liable or responsible
for the content.)
- Vicomsoft develops and provides Network
Address Translation and TCP/IP routing technology, including PPP and
PPPoE features. Our software allows users to connect whole LANs to the
Internet, using single or multiple Internet connections.
Vicomsoft have gained significant experience in the domain
of the TCP/IP protocol suite including PPP and PPPoE, and would like to
make this information available to those interested in this subject.
For those who would like to study this subject in more detail
useful links are listed at the end of this document.
1. What is PPP?
2. What is PPPoE?
3. Who uses PPPoE?
4. How do I know if I need PPPoE software?
5. What does Vicomsoft recommend?
Download this article as a .PDF
- 1. What is PPP?
PPP is an acronym for Point to Point Protocol. It is a
member of the TCP/IP suite of network protocols.
PPP is an extension to TCP/IP that adds two additional sets of functionality:
- it can transmit TCP/IP packets over a serial link
- it has login security
TCP/IP by itself cannot be transmitted over a serial
link. This makes it unsuitable for WANs (Wide Area Networks). At the
time of this writing it is not feasible to extend an Ethernet network
over many thousands of miles although this may soon change using 10
Gigabyte Ethernet over fibre optic. Telecommunications companies however
offer serial communications links around the globe right now and have
done so for many years. To make TCP/IP work over these serial links,
it was necessary to create a protocol that could transmit TCP/IP packets
over serial lines. The two protocols that do this are:
PPP is more feature rich and has largely supplanted SLIP.
- SLIP (Serial Line Internet Protocol)
When serial links that are part of the public telephone
system are used, care must be taken to ensure the authenticity of all
communications. To this end PPP incorporates user name and password
security. Thus, a router or server receiving a request via PPP where
the origin of the request is not secure, would require authentication.
This authentication is part of PPP. Because of its ability to route
TCP/IP packets over serial links and its authentication capabilities,
PPP is generally used by Internet Service Providers (ISPs) to allow
dial-up users to connect to the Internet.
Figure 1: PPP is used by Internet
Service Providers (ISPs) to allow dial-up users to connect to the Internet.
2. What is PPPoE?
PPP, which was designed for serial communications,
has now been adapted to Ethernet, and is appropriately called PPP over
Ethernet (PPPoE). Since PPP was designed to do things that were either
impossible or unnecessary with Ethernet, users are often confused as to
why one would want to use PPP over Ethernet at all.
If we were to compare TCP/IP traffic to
vehicle traffic, the basic TCP/IP protocol would be comparable to a network
of city streets. Streets can serve many access points. It is easy to get
on to and off of the street. Additional access points can be added with
little disruption. It is hard to tell how many cars are actually using
each street. PPP, on the other hand, would be comparable to a railway.
Travel is generally between two well defined points. You can't get on
and off anywhere. It is relatively easy to count and monitor passengers.
You need a ticket to board.
If this is true, then isn't PPPoE like running railway
tracks down main street? In fact, yes, it is. That is what tramways do.
Without disturbing main street traffic, they bring the advantages of railways.
They offer speedy access between two well defined points and allow you
to count passengers. And you need a ticket to board.
Figure 2: PPPoE allows ISPs to monitor
the volume of traffic that their users generate.
PPP over Ethernet brings this sort of functionality to
ISPs that do not use serial links to connect their users. Serial ISPs
already use PPP over modem communications. DSL providers on the other
hand use Ethernet, not serial communications. Because of this, many
require the added functionality of PPP over Ethernet, which allows them
to secure communications through the use of user logins and have the
ability to measure the volume of traffic each user generates.
3. Who uses PPPoE?
To the best of our knowledge, only DSL providers are actually
using PPPoE right now. It is likely, however, that cable modem providers
will begin doing so in the near future.
4. How do I know if I need PPPoE
DSL providers that require the use of PPPoE generally supply
their choice of PPPoE software to their subscribers. This is fine if you
are connecting a single computer to the Internet via DSL. For users that
connect an entire LAN to the Internet via DSL, the software supplied by
the DSL provider may be insufficient. There may be compatibility problems
with the router or Internet sharing software in use between the LAN and
the DSL connection. You will need to consult your DSL provider about this.
Figure 3: PPPoE on a Local Network.
5. What does Vicomsoft recommend?
If you are connecting a single computer to the Internet
via DSL with PPPoE, the software supplied by the DSL provider may be sufficient
but there are alternatives. InterGate Policy Manager from Vicomsoft offers full support for PPPoE, and may optionally provide
teaming of multiple Internet connections for increased bandwidth as well
as parental controls. If you are connecting a LAN to the Internet via
DSL with PPPoE, the most economical way to do so is to use a single public
IP address allocated by your DSL ISP, and share it across your LAN with
Internet sharing hardware or software. This is only practical if the Internet
sharing hardware or software is PPPoE compatible. If your vendor's web
site has a search function, use it to search "PPPoE" and you will quickly
find out if they support it or not.
PPPoE is a standard, and you might assume that all solutions
are therefore 'equal'. As in most things, some are more equal than others.
The standard requires that PPPoE software add an additional header to
the beginning of each TCP/IP packet. This may cause the packet to become
larger than the maximum allowable size. Some software solutions handle
this transparently, but some require you to modify the TCP/IP settings
on all of the client computers on the LAN.