SNR S2989G-48TX-RPS — настройка функций безопасности в сетевых протоколах PPPoE [349/553]

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S2989G-24TX Operation Manual

Chapter 6 Security Function Configuration

6-76

network is also developing from strength to strength, but security problem gradually

becomes the focus, soever the clients or the access device and the network are faced

with security problem (especially from the client) in the current access network. Traditional

Ethernet user can not be identified, traced and located exactly, however in exoteric and

controllable network, identification and location are the basic character and requirement

for user, for example, when supplying the application that use user accounts to login, this

method supplied by PPPoE Intermediate Agent can availably avoid user accounts

embezzled.

There are two stages for PPPoE protocol work: discovery stage and session stage.

Discovery stage is used to obtain MAC address of the remote server to establish a point-

to-point link and a session ID with the server, and session stage uses this session ID to

communicate. PPPoE Intermediate Agent only relates to discovery stage, so we simply

introduce discovery stage.

There are four steps for discovery stage:

1. Client sends PADI packet: The first step, client uses broadcast

address as destination address and broadcast PADI (PPPoE

Active Discovery Initiation) packet to discover access collector in

layer 2 network. Notice: This message may be sent to many

access collector of the network.

2. Broadband Access Server responds PADO packet: The second

step, server responds PADO (PPPoE Active Discovery Offer)

packet to client according to the received source MAC address of

PADI packet, the packet will take sever name and service name.

3. Client sends PADR packet: The third step, client selects a server to

process the session according to the received PADO packet. It may

receives many PADO packets for PADI message of the first step

may be sent to many servers (select the server according to

whether the service information of PADO packet match with the

servce information needed by client). MAC address of the other

end used for session will be known after server is selected, and

send PADR (PPPoE Active Discovery Request) packet to it to

announce server the session requirement.

4. Server responds PADS packet: The fourth step, server establishes

a session ID according to the received PADR packet, this session

ID will be sent to client through PADS (PPPoE Active Discovery

Session-confirmation) packet, hereto PPPoE discovery stage is

completed, enter session stage.

PADT (PPPoE Active Discovery Terminate) packet is an especial packet of PPPoE,