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12.3 L2TP
12.3.1 Brief Introduction of L2TP
L2TP-Layer Two Tunneling Protocol
The data has no encryption mechanism and the data security can be ensured through IPSEC.
It is different from layer 3 VPN (IPSec \ GRE) that L2TP is to encapsulate the private data from
the user network from the layer 2 PPP header, while layer 3 VPN is to encapsulate the private
data from the user network from the layer 3 IP header.
Main purposes: overseas agencies and mission personnel from remote via a public network
through virtual tunnels and the corporate headquarters of the network connection.
12.3.2 Brief Introduction of L2TP Protocol
12.3.2.1 Encapsulation Hierarchy of L2TP Packet
The format of this packet is the data packet between LAC and LNS.
L2TP packet header is the packet header of VPN protocol. It is encapsulated with PPP packets;
therefore L2TP is a layer 2 VPN protocol.
12.3.2.2 Data Forwarding and Packaging Process
As shown in the above typical networking diagram, Dialer is a VPN user. VPN user sends data
to LNS and first send data to LAC with the format as shown below. It shows that the data in
this segment is not subject to L2TP protection.
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