1. NAD710 - Introduction to Networks Using Linux Network Address Translation May 28, 2003 Professor Tom Mavroidis
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3. The long-term solutions consist of various proposals for new Internet protocols with larger addresses (IPv6) When CIDR failed to further maintain the IP internet structure, there came another proposal : N A T NAT is not a very far reaching or long term solution But at least it is very fast, provides extra time until better solutions are designed and almost independent from the outer networks. Proposals
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5. NAT is translation of either a subset or all of the IP addresses in a sub domain to globally unique address(es). From an operational point of view, it is a function imposed on the router. That is a router on the gateway border to be configured as a Network Address Translator. What is NAT?
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9. IP chains flow of events: Local processes CRC INPUT chain Inbound packet OK Malformed? garbage yes error Deny-reject Accept packet Routing algorithm Local destination Outbound packet Malformed? forwarded packet no no FORWARD chain Deny-reject yes Malformed? yes Outbound packet no OUTPUT chain Deny-reject Outbound packet
10. Enable IP forwarding for the kernel Execute: echo “1” > /proc/sys/net/ipv4/ip_forward Or make it permanent ( persistent between boots ) with assigning the variable IP_FORWARD = yes in /etc/sysconfig/sysctl file This will ensure basic router functionality Use /sbin/ipchains-save > afilename to save the rules Use /sbin/ipchains-restore < afilename to restore the rules To get this thing going
11. IP chains syntax ipchains –[flags] [input | outout | forward | custom_chain] [options] [action] ipchains –M [-L | -S] [options] A very simple example with IP Masquerading: ROUTER WITH NAT 10.1.1.1 eth1 202.7.1.19 eth0 Internet Internal net 10.0.0.0
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16. IP tables syntax iptables –[flags] [chain] [options [extentions] ] [action] Syntax and examples: A very simple example with Static IP Translation: ROUTER WITH NAT 10.1.1.1 eth1 202.7.1.19 eth0 www ftp 10.1.1.4 10.1.1.5 Internet Internal net 10.0.0.0/8
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