PPPoE Passthrough Questions
Posted by on 17 January 2012 04:00 PM

PPPoE Passthrough Questions



The distributor is talking to some enterprise size customers over the last few weeks & have been promoting Draytek PPPoE passthrough feature for use on larger platform devices e.g. Cisco PIX/ASA, Juniper SSG/Netscreen for ADSL PPPoA connectivity. As a result  some questions have been raised about the mechanics of what the Draytek does & what kinds of responses should be expected to/from LCP requests etc...


I have listed specific questions below but what they need  is an overview of the process & what it does. They often come up against the 'Cisco houses' where an integrator simply won't take a demo box from another vendor & commit their time to test for themselves. In these cases as there is no documentation to support them,  they have to rely on how we 'guess' the system operates to convince them.

Some general questions:
1) Is the MAC address spoofed as in 1/2 bridge mode?
2) How are PPPoE LCP echo request packets handled?
3) Does the modem pass PPPoA up & down signals back to the PPPoE client via PPPoE Active Discovery Terminate (PADT) / Session-confirmation (PADS) packet or would an internal firewall/server rely on LCP echo requests failing to determine if the DSL link is down?
4) Is the feature fully RFC-2516 compatible



I think the customer is asking the PPPoA relay function on Vigor adsl routers.

The answers are below for your reference.

1)      If the 1/2 bridge mode means the PPPoA relay function.

No, Vigor router will use its real MAC/ LAN MAC to communicate with the PPPoE client.

2)      Vigor acts as PPPoA/E relay will help to maintain the ppp session for client and the ppp session from server.

Vigor will not send LCP but forward LCP request and response between server and client.

3)      It depends on the client.

Vigor acts as PPPoA/E relay will not send out PADT or LCP Terminate to server if it doesn't receive such packets from client.

4)      I cannot be sure - since this function is different from PPPoE passthrough.



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