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NATs (Network Address Translators)

NATs (Network Address Translators). Henning Schulzrinne Dept. of Computer Science Columbia University Fall 2003. NATs. Network address translation = local, LAN-specific address space translated to small number of globally routable IP addresses Motivation: scarce address space

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NATs (Network Address Translators)

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  1. NATs (Network Address Translators) Henning Schulzrinne Dept. of Computer Science Columbia University Fall 2003

  2. NATs • Network address translation = local, LAN-specific address space translated to small number of globally routable IP addresses • Motivation: • scarce address space • cost: about $9k/year for up to 262,000 addresses • prevent home broadband users from running servers at home • security: prevent unsolicited inbound requests • avoid renumbering if provider changes • most small/mid-sized LANs inherit address space from ISP

  3. Prevalence of NATs • Claim: 50% of broadband users are behind NATs • All Linksys/D-Link/Netgear home routers are NATs • Measurement: for Quake III users, about 17-25% using NAT (May/June 2001)

  4. NAT details • RFC 1631 (first description) • RFC 1918 (private-use addresses) • RFC 2663 • RFC 2776 • RFC 3022 • RFC 3027 • RFC 3235 • RFC 3424 • RFC 3489 (STUN)

  5. NAT types • All use net-10/8 (10.*.*.*) or 192.168/16 (172.16/12 also available) • Address translation • Address-and-port translation (NAPT) • most common form today, still called NAT • one external (global) IP address

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