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ATTENTION! This topic covers firmware functionality that is only supported in firmware V3.54+ and, hence, only available on second-generation Devices (EM120, EM200, EM203(A), DS203).
PPPoE family of protocols is mostly used by ADSL modems. Some ADSl links (modems) are of "always on" type and do not require any link establishment. Other ADSL links require link establishment procedure based on PPPoE protocol that is very similar to that of old-style POTS dial-up modems. In fact, PPPoE means "PPP over Ethernet"- it is an Ethernet adaptation of an old PPP (point-to-point protocol) used with dial-up modems. If the DS is directly connected to such an ADSL modem it will need to establish a PPPoE link in order to connect to any remote network host (i.e. network host residing on a different network segment)*.
PPPoE only affect communications with remote network hosts, i.e. hosts that reside on a different network segment (local segment boundaries are defined by the Netmask (NM) setting). With PPPoE enabled, all communications with remote hosts are effected through PPPoE link and not default gateway (therefore, Gateway IP-address (GI) setting is irrelevant in this case).
PPPoE is enabled through PPPoE Mode (PP) setting. PPPoE protocol includes authentication phase (login). PPPoE login name and password are defined by PPPoE Login Name (PL) and PPPoE Login Password (PD) settings. Several authentication protocols are defined for PPPoE. Currently, the DS only supports authentication through a protocol called PAP.
The PPPoE Mode (PP) setting offers two options that define when PPPoE link is established. When this setting is at 1 (on connection) the link is established when the DS needs to open a data connection to a remote host. The link is terminated 30 seconds after the data connection is closed. When this setting is at 2 (on powerup) the PPPoE link is established during powerup procedure. The DS then attempts to maintain this link at all times and re-establishes the link if it is broken.
With any PPPoE link both sides have to agree on the IP-addresses that will be used on each side of the link. IP-address on the DS side is requested from and supplied by the Access Concentrator. This IP-address has nothing to do with the "main" IP-address of the DS which is defined by IP-address (IP) setting or supplied by DHCP server when DHCP (DH) setting= 1 (enabled). Just like on PC, a PPPoE link becomes a "virtual" network card (interface) of the DS. As such, it has its own IP-address. This does not affect operation of the DS in any way since it is, actually, not important which IP-address is used for PPPoE link- as long as the Access Concentrator is "satisfied" with this address.
* PPPoE is not required if the DS is connected to the ADSL modem through a router that supports PPPoE. In this case it is the job of this router to take care of PPPoE link management.