ORiNOCO BG-2000, Руководство пользователя

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Virtual Private Networks
8-4
L2TP Overview
L2TP is a tunneling protocol that encapsulates PPP frames to be sent over
a public network. L2TP uses UDP and L2TP messages for tunnel
maintenance. L2TP also uses UDP to send L2TP-encapsulated PPP
frames as the tunneled data. The payloads of encapsulated frames can be
encrypted and/or compressed. Because L2TP uses UDP for encapsulating
PPP frames, it utilizes more command and control messages than PPTP.
However, because of the additional messages, L2TP tunnels perform better
over high latency networks.
The L2TP client and L2TP server must first establish a UDP connection.
Once connected, L2TP creates the tunnel in which L2TP datagrams will
traverse the public network.
Differences between PPTP and L2TP
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PPTP requires that the public network be an IP network. L2TP can be
used over IP (using UDP), Frame Relay Permanent Virtual Circuits
(PVCs), X.25 virtual circuits (VCs), or ATM VCs.
■
PPTP can only support a single tunnel between endpoints. L2TP allows
for the use of multiple tunnels between endpoints.
■
When header compression is enabled, L2TP operates with 4 bytes of
overhead, as compared to 6 bytes of overhead with PPTP.
■
L2TP provides for tunnel authentication while PPTP does not.
■
PPTP uses a TCP connection while L2TP uses a UDP connection.