Lecture-17 - Lecture #17 Todays Lecture Objectives NAT CDNs...

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Lecture #17
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Today’s Lecture Objectives • NAT • CDNs 2P networks • P2P networks
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NAT: Network Address Translation • Motivation: local network uses just one IP address as far as outside word is concerned: – no need to be allocated range of addresses from ISP: - just one IP address is used for all devices – can change addresses of devices in local network without notifying outside world – can change ISP without changing addresses of devices in local network – devices inside local net not explicitly addressable, visible by outside world (a security plus).
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NAT: Network Address Translation 10.0.0.1 10.0.0.2 10.0.0.4 138.76.29.7 local network (e.g., home network) 10.0.0/24 rest of Internet 10.0.0.3 Datagrams with source or destination in this network have 10.0.0/24 address for source, destination (as usual) All datagrams leaving local network have same single source NAT IP address: 138.76.29.7, different source port numbers
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NAT: Network Address Translation outgoing datagrams: replace (source IP address, port #) of every outgoing datagram to (NAT IP address, new port #) . . . remote clients/servers will respond using (NAT IP address, new port #) as destination addr. remember (in NAT translation table) every (source IP address, port #) to (NAT IP address, new port #) anslation pair translation pair incoming datagrams: replace (NAT IP address, new port #) in dest fields of every incoming datagram with corresponding (source IP address, port #) stored in NAT table
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NAT: Network Address Translation 10.0.0.1 S: 10.0.0.1, 3345 D: 128.119.40.186, 80 1: host 10.0.0.1 sends datagram to 128.119.40, 80 NAT translation table WAN side addr LAN side addr 138.76.29.7, 5001 10.0.0.1, 3345 …… …… 2: NAT router changes datagram source addr from 10.0.0.1, 3345 to 138.76.29.7, 5001, updates table 10.0.0.2 10.0.0.3 1 10.0.0.4 138.76.29.7 S: 128.119.40.186, 80 D: 10.0.0.1, 3345 4 S: 138.76.29.7, 5001 D: 128.119.40.186, 80 2 S: 128.119.40.186, 80 D: 138.76.29.7, 5001 3 3: Reply arrives dest. address: 138.76.29.7, 5001 4: NAT router changes datagram dest addr from 138.76.29.7, 5001 to 10.0.0.1, 3345
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This note was uploaded on 02/19/2012 for the course ENGR 361 taught by Professor Drexel during the Spring '12 term at Bloomsburg.

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Lecture-17 - Lecture #17 Todays Lecture Objectives NAT CDNs...

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