Using IP Prefixes, AS Numbers and Domain Names in Examples

Keep in mind: Use private IP addresses, AS numbers and domain names in all technical documentation you're producing (unless, of course, you're describing an actual network). If you're forced to use public addresses or AS numbers (for example, to illustrate how the neighbor remote-private-as command works), you should clearly state that they are imaginary.

You can safely use:



2-byte ASN

4-byte ASN

Domain names

Revision History

Cleaned up the blog post as part of winter 2020 cleaning. Added IP IPv6 documentation prefix.
Added documentation IPv4 prefixes, 2-byte ASN and 4-byte ASN (RFC 5737, RFC 5398) suggested in comment by Charles Monson.


  1. You may be interested to know that there is also a reserved IP range for testing as well documeneted in RFC2544. I blogged it here

    (Hope its OK to reference the article)

  2. For a laugh, have a read of the Spam Filtering writeup on -

    This guy has been suffering from non-compliance with RFC 2606 for years, his domain even appeared in the 1999 HTML 4.01 spec as an example domain - and he has had to really look into blocking spam.
  3. @gregferro: Of course it's OK to reference the article relevant to the topic (and I would silently delete the comments about blue life-enhancing pills :).
  4. Worth a note that there are IPv4 prefixes reserved specifically for documentation/examples in RFC5737. The prefixes are, , and

    There are also documentation ASN in RFC5398. Those ranges are 64496 - 64511 and 65536 - 65551.

  5. @Charles: Thanks a million. Added.

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