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RFC · NetworkingStandard explained

RFC 1918: Private IPv4 address spaces

Summary

RFC 1918 reserves three IPv4 ranges for internal networks that are not routed globally. Private addresses extended the life of IPv4 but created lasting NAT and merger problems. Non-global addressing is no substitute for access control.

Ideas

  • 10/8, 172.16/12 and 192.168/16 are reserved for private networks.
  • Routers on the public internet should not forward these prefixes.
  • Overlapping addresses make later network interconnections difficult.

Facts

  • RFC 1918 replaces RFC 1597.

Remarks

  • RFC 1918 has the status “Best Current Practice”; current errata and successor documents should also be checked.

Recommendations

  • Choose internal prefixes with VPNs and company mergers in mind.
  • Filter private source addresses at external borders.

References

Read the RFC at the RFC Editor

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