RFC 4282:The Network Access Identifier
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Layer 2


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... Point-to-Point Tunneling Protocol (PPTP) [RFC2637], the Layer 2 Forwarding (L2F) protocol [RFC2341 ...
... Forwarding (L2F) protocol [RFC2341], the Layer 2 Tunneling Protocol (L2TP) [RFC2661], and the IPsec tunnel mode ...



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