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Reference.org
Layer 2 Tunneling Protocol
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<p>In <a href="/facts/Computer_network/3w5RM99p">computer networking</a>, Layer 2 Tunneling Protocol (L2TP) is a <a href="/facts/Tunneling_protocol/jKaT1Czc">tunneling protocol</a> used to support <a href="/facts/Virtual_private_network/HX1WUQ3E">virtual private networks</a> (VPNs) or as part of the delivery of services by ISPs. It uses encryption ('hiding') only for its own control messages (using an optional pre-shared secret), and does not provide any <a href="/facts/Encryption/16q29Fdv">encryption</a> or <a href="/facts/Confidentiality/JFMubsQm">confidentiality</a> of content by itself. Rather, it provides a tunnel for Layer 2 (which may be encrypted), and the tunnel itself may be passed over a Layer 3 <a href="/facts/Encryption_protocol/0WuyTkFo">encryption protocol</a> such as <a href="/facts/IPsec/01MwcET1">IPsec</a>. </p>