Transmitting PPP Over Ethernet PPPoE and Windows 2000 Pro

PPPoE is a method for establishing PPP connections through Ethernet network
adapters. See RFC2516 : Transmitting PPP Over Ethernet PPPoE. Many DSL
providers use PPPoE to maintain the familiar “dial-up” experience when users
connect to the Internet through a DSL modem (and to control the number of their
IP addresses used by their DSL users).

PPPoE requires a MTU ( Maximum Transmission Unit ) setting on all client
computers of 1492 or less. This includes any computers you have accessing the
Internet via an ICS ( Internet Connection Sharing ) connection. The symptom when
the MTU is too large is an inability to browse some Web sites or send e-mail
messages that contain attachments. To check your MTU setting:

  • Determine the default gateway of the ICS server using ipconfig
  • From a client, type ping -f -l MTU size IP address
    of default gateway from first step

  • Start with an MTU size of 1454. If this fails with an error message
    indicating that it must be fragmented, decrease the MTU size and try again.
    Repeat this until the ping command succeeds.

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