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Specify prefixes to advertise

List all prefixes and the ASNs from which you want them to originate.

When specifying prefixes, observe these guidelines:

  • Prefixes must support at least 256 hosts (/24 in classless inter-domain routing [CIDR] notation).
  • Internet Routing Registry entries and Letters of Authorization must match the prefixes and originating prefixes you submit to Cloudflare.
  • When using contiguous prefixes, specify aggregate prefixes where possible.
  • When using Route Origin Authorizations (ROAs) to sign routes for resource public key infrastructure (RPKI), the prefix and originating ASN must match the onboarding submission.
  • If you do not own an ASN, you may use our Cloudflare Customer ASN (AS209242) as the originating AS.

For an example prefix configuration, refer to this table:

PrefixOriginating AS
103.21.244.0/23AS209242
131.0.72.0/22AS395747
103.21.245.0/24AS395747