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Chapter 10 - Configuring PPPoE/Bridged Mode On ADSL
Chapter 10 - Configuring PPPoE/Bridged Mode
On ADSL
Introduction
This chapter familiarizes the user with:
• Configuring PPPoE and Bridged Mode Links
• Viewing status
ADSL Fundamentals
An ADSL (Asymmetric Digital Subscriber Line) line is a communications link
running over regular POTS telephone service. The link is asymmetric, supporting
data transfer at up to 8 Mbps from the network and up to 1 Mbps to the network. The
actual bandwidth depends upon the distance between the router and telco central
office, the maximum distance of which may be up to 5480 m. An ADSL card must
connect to a central ADSL DSLAM for its connection.
ADSL shares ordinary telephone lines by using frequencies above the voice band.
ADSL and voice frequencies will interfere with each other. If the line will be used for
both data and voice, a “splitter” should be installed to divide the line for DSL and
telephone.
ADSL is almost always used to make a connection to the Internet via an ISP. There
are two methods for establishing the connection, PPPoe and Bridged mode.
ADSL uses the ATM protocol to communicate with the central office DSLAM. ATM
uses virtual channels to route traffic and the DSL connection needs to know which
virtual channels to use. Most providers use VPI=0 and VCI=35. There are exceptions
to this. Some providers that use different settings are listed in the following table.
Provider VPI VCI
Typical Provider 0 35
Bell South 8 35
New Edge 0 38
Sprint 8 35
US West/Qwest 0 32
PPPoE/Bridged Mode Fundamentals
In PPPoE (Point-to-Point Protocol Over Ethernet) the PPP dial-up protocol is used
with Ethernet over ADSL as the transport. PPPoE supports the protocol layers and
authentication widely used in PPP and enables a point-to-point connection to be
established in the normally multipoint architecture of Ethernet.
As your PPPoE connection is established a PPP interface will be created. The name
will be “pppX” where X is the same as the interface number. Use this interface name
in firewall rules.
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