H3C Technologies H3C SecPath F5020 - Manual (Page 33)

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Figure 7 NAS-initiated tunneling mode
A NAS-initiated tunnel has the following characteristics:
• The remote system only needs to support PPP, and does not need to support L2TP.
• Authentication and accounting of the remote system can be implemented on the LAC or the LNS.
Figure 8 Establishment process for NAS-initiated tunnels
As shown in Figure 8 , the following workflow is used to establish a NAS-initiated tunnel:
1. A remote system (Host A) initiates a PPP connection to the LAC (Device A).
2. The remote system and LAC perform PPP LCP negotiation.
3. The LAC authenticates PPP user information of Host A by using PAP or CHAP.