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:
| Prefix | Originating AS |
|---|---|
| 103.21.244.0/23 | AS209242 |
| 131.0.72.0/22 | AS395747 |
| 103.21.245.0/24 | AS395747 |