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PPTP

PPTP. Point-to-Point Tunneling Protocol (PPTP) Problem: PPP was created for dialing into a local RAS server But the site’s RAS may be far away Long-distance calls are expensive. RAS. Long-Distance Call. PPTP. Point-to-Point Tunneling Protocol (PPTP)

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PPTP

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  1. PPTP • Point-to-Point Tunneling Protocol (PPTP) • Problem: PPP was created for dialing into a local RAS server • But the site’s RAS may be far away • Long-distance calls are expensive RAS Long-Distance Call

  2. PPTP • Point-to-Point Tunneling Protocol (PPTP) • We would like PPP to work over the Internet to avoid long-distance telephone charges • But PPP is only a data link layer protocol • It is only good for transmission within a subnet (single network) RAS

  3. PPTP • The Point-to-Point Tunneling Protocol (PPTP) makes this possible • Created by Microsoft • Widely used Access Concentrator RAS

  4. PPTP • PPTP Operation • User dials into local PPTP access concentrator host • User sends the access concentrator a PPP frame within an IP packet Access Concentrator RAS Packet

  5. PPTP • PPTP Operation • Access concentrator places incoming IP packet within another IP packet • Sends packet to the distant RAS Access Concentrator RAS Encapsulated Packet

  6. PPTP • PPTP Operation • Distant RAS removes the original packet • Treats the packet as if it came in over a local telephone line • Deals with the PPP frame within the packet RAS Original IP Packet

  7. PPTP • PPTP Encapsulation • Access concentrator receives the original IP packet, which has the destination IP address of the access concentrator • Adds a new IP header with the IP address of the RAS • Adds an enhanced general routing encapsulation (GRE) header for security Original IP Packet Enhanced GRE Header New IP Header

  8. PPTP • PPTP Tunneling • Encapsulating an IP packet within another packet to send it through a network is called tunneling • This is how tunneling mode works in IPsec (discussed earlier in the module) RAS Tunnel Access Concentrator

  9. PPTP • Remote Access Server (RAS) is a widely used term • PPTP documentation calls them network access servers (NASs) • Same meaning but different names RAS NAS =

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