What are the private ASN ranges?

16-bit private ASNs: 64512–65534. 32-bit private ASNs: 4200000000–4294967294. ASN 65535 and 4294967295 are reserved.

When should I use a private ASN?

Use a private ASN for internal BGP routing within your organization when you don't need to establish public BGP peering. If you need to peer with ISPs or participate in internet routing, you need a public ASN.

Will private ASNs appear in internet routing tables?

They should not. ISPs are expected to filter private ASNs from BGP announcements. If you see private ASNs in an AS_PATH from the public internet, it indicates a routing policy misconfiguration.

Redes

Private ASN Ranges: 64512–65534 and 4200000000+

Just like private IP addresses (RFC 1918), there are private ASN ranges reserved for internal use that should not appear in the global BGP routing table. Private ASNs allow organizations to use BGP internally without consuming a globally unique ASN allocation.

Cómo Funciona

The IANA has reserved two private ASN ranges: 64512–65534 for 16-bit ASNs and 4200000000–4294967294 for 32-bit ASNs. These are analogous to RFC 1918 private IP space. Private ASNs are used in internal BGP topologies, lab environments, and service provider configurations where BGP is needed but without peering with the public internet. They must be stripped (using AS_PATH manipulation) before routes are advertised externally.

Por Qué Importa

Using private ASNs for internal routing avoids consuming the limited public ASN space. They are commonly used by enterprise networks running BGP with their ISP under a provider-assigned public ASN, where internal BGP domains use private ASNs that get stripped at the edge.

Problemas Comunes

Private ASNs leaking into public BGP routing tables (should be filtered by ISPs)
AS_PATH containing private ASNs visible to external peers — indicates misconfigured stripping
Confusion between 16-bit (up to 65535) and 32-bit ASN format

Herramientas de Diagnóstico

ASN Lookup