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rvh
Asked: 2024-04-23 22:15:10 +0800 CST

Is AS0 (zero) ASN invalid or reserved?

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I read in some places that AS0 is reserved.

Wikipedia says:

AS0 is used by all five RIRs to invalidate unallocated space.

Assume it means no valid traffic ever comes from AS0.

I just want to use it as a placeholder in a Cloudflare access list to leave a general note.

Just making sure this doesn't interfere with users accessing our sites even if a block rule is applied.

as-number

1 Answers

  1. Best Answer

    Reserved AS, invalid ROA.

    Autonomous System 0 is reserved by IANA for resources not in use. RFC 7607 clarifies:

    [RFC6491] specifies that AS 0 in a Route Origin Attestation (ROA) is used to mark a prefix and all its more specific prefixes as not to be used in a routing context. This allows a resource holder to signal that a prefix (and the more specifics) should not be routed by publishing a ROA listing AS 0 as the only origin. To respond to this signal requires that BGP implementations not accept or propagate routes containing AS 0.

    Do not associate prefixes you use to AS 0. It is not an unused AS, it is how bogons and RIR unallocated space are dropped.

    See also: BGP Origin Validation workshop

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