In the Active Discovery phase of PPPoE, which of the following is NOT verified by the Broadband Network gateway (BNG) to prevent spoofing?
A. source MAC address
B. arriving access interface
C. PPPoE session ID
D. destination MAC address
Explanation:
The destination MAC address is the address of the BNG, so there is no need for it to be verified. If the traffic arrived on the BNG interface, it is correct.
PPPoE is composed of two main phases, the Active Discovery Phase and the PPP Session Phase. The Active Discovery phase consists of the following communications between the PPPoE client and the BNG:
1. The client sends a PPPoE Active Discovery Initiation (PADI) broadcast signal to the remote device (BNG).
2. The remote device sends back a PPPoE Active Discovery Offer (PADO) that contains the MAC address of the BNG and destination MAC address of the subscriber (client).
3. The subscriber (client) send a PPPoE Active Discovery Request (PADR) continuing the destination MAC address of the BNG to which it wishes to establish a session.
4. The BNG responds with a PPPoE Active Discovery Session-Confirmation (PADS) containing the PPPoE session ID.
Once this process is complete, the session moves on to the PPP Session Phase in which Link Control Protocol (LCP) parameters such as maximum transmission unit (MTU) are agreed to, authentication is performed, and Network Control Protocols (NCP) for any Layer 3 protocol that will traverse the link are started.
Objective:
Layer 2 Technologies
Sub-Objective:
Configure and verify PPP