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NAT

NAT. Network Address Translation. Private IP Address . • Unique address will be exhausted. • Defined in RFC 1918 • Address range:. NAT : IP Masquerade . Defined in RFC 1631. ?. router. 140.113.56.71. 198.168.1.2. NAT applications. Modem Connections To the Internet

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NAT

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  1. NAT Network Address Translation

  2. Private IP Address • Unique address will be exhausted. •Defined in RFC 1918 • Address range:

  3. NAT : IP Masquerade • Defined in RFC 1631 ? router 140.113.56.71 198.168.1.2

  4. NAT applications • Modem Connections To the Internet -- IP masquerading • Multiple Servers -- port forwarding • Transparent Proxying -- redirection

  5. NAT applications (2)

  6. NAT on Linux • Linux 2.2 -ipchains + ipmasqadm Three kinds of chains (rules on packets): input:as packets come in output:as packets out forward:as packets pass by

  7. Simple examples ipchains -P forward –j DENY ipchains-A forward -b –s 192.168.0.0/24 –d 0/0 -j MASQ echo 1 > /proc/sys/net/ipv4/ip_forward 啟動 IP masquerade Ipmasqadm portfw –a –P tcp –L 1.2.3.4 8080 192.168.1.1 80 做 Port forwarding , 所有到 1.2.3.4 8080的封包都會被 Forward到 192.168.1.1 80

  8. NAT on Linux • Linux 2.4 -iptables Three kinds of chains : PREROUTING:as packets come in POSROUTING:as packets leave OUTPUT:locally-generated packets

  9. Example iptabes -t nat –A POSTROUTING –o ppp0 –j MASQUERADE 啟動 IP msquerade Iptables –A PREROUTING –t nat –p tcp –d 1.2.3.4 –dport 8080 –j DNAT –to 192.168.1.1:80 IP forward packets to 192.168.1.1:80

  10. 參考資料 • Linux 2.4 NAT HOWTO • www.study-area.org • Linux Security Toolkit David A. Bandel

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