Getting an ASN in the RIPE region: what you need before you apply

An Autonomous System Number lets your network run BGP under its own identity, announce its own prefixes and choose its own upstreams. Requesting one in the RIPE region isn’t complicated, but requests move faster when the groundwork is done first. This article covers what to prepare, why the registry asks for it, and what to set up once the number is assigned.

Why does the registry ask for a justification?

AS numbers are a shared resource, and RIPE community policy ties assignment to need. In general terms, an ASN exists to express a routing policy that differs from your upstream’s. In practice that usually means connecting to more than one other network (multihoming) and making your own routing decisions about what to announce and accept.

The exact criteria are set out in the current RIPE NCC policy on AS number assignment, and policy can change through the community’s policy development process. Read the current version before you apply rather than relying on summaries, including this one.

If you have a single upstream and no plans for another, you may not need an ASN yet:

• Your upstream can originate your prefixes from its own AS, with route objects and ROAs that name it.
• You can run BGP with your upstream using a private ASN, which the upstream removes before announcing your prefixes. The private ranges are 64512–65534 (16-bit) and 4200000000–4294967294 (32-bit).
• If timing matters, an existing ASN can sometimes be transferred to you, where policy allows.

Own LIR or sponsoring LIR?

You can request an ASN in one of two ways:

• Through your own LIR, if your organisation is a RIPE NCC member. You submit the request in the LIR Portal.
• Through a sponsoring LIR, if you aren’t a member. You sign an end user agreement with the sponsor, which submits the request and maintains the contractual link with the RIPE NCC.

Either way, your organisation is the holder. Choose the route before collecting documents, because your sponsor or the RIPE NCC will run due diligence on your company and ask for registration documents and contact details.

What to have ready before you apply

Use this as a pre-application checklist:

1. Legal entity details. Your company name exactly as registered, its address, and a recent extract from the company register.
2. Intended peers. The ASNs of the networks you plan to connect to, such as transit providers or internet exchange route servers. Have contact details or agreements ready in case you’re asked to show that the connections are real.
3. A description of your routing policy. What you’ll announce to each peer and what you’ll accept from them. You may be asked to express it as RPSL import: and export: lines; it doesn’t need to be elaborate.
4. IP space to announce. An ASN with nothing to announce is hard to justify. The space can be PI, an LIR allocation or leased. If it’s leased, you’ll need the holder’s authorisation, usually a letter of authorisation (LOA), and their help with route objects and ROAs.
5. RIPE Database objects. An organisation object, a mntner you control, and role objects for admin, technical and abuse contacts. Getting these right at the start saves untangling them later.
6. Technical readiness. Routers that support BGP with four-byte ASNs, and a named person who will configure and monitor the sessions.

Inconsistencies between your request and the database, such as a different company name or contacts that don’t respond, can lead to follow-up questions. Check them before you submit.

16-bit or 32-bit?

New assignments are normally 32-bit (four-byte) ASNs; 16-bit numbers are scarce. If you have a specific reason to want one, ask the RIPE NCC or your sponsor about availability.

Current router software handles 32-bit ASNs without difficulty. The practical difference is BGP communities: standard communities hold an AS number in 16 bits, so a 32-bit ASN can’t be expressed in them directly. Large BGP communities (RFC 8092) solve this and are widely supported, but if you depend on community-based traffic engineering, confirm that your upstreams and exchange route servers accept them.

What to do once the ASN is assigned

When the aut-num object appears in the RIPE Database:

• Create route and route6 objects for the prefixes you’ll announce, and ROAs naming your new AS.
• Create an as-set if you’ll have downstream customers, and give its name to your upstreams.
• Add your network to PeeringDB if you plan to peer at internet exchanges.
• Once traffic has moved, remove or update route objects and ROAs that still name your previous upstream’s AS.
• Keep the aut-num’s contacts current. It’s the first place other operators look when something goes wrong.

Use the ASN for the purpose you described. The assignment rests on the need you stated, and a number that sits unused for a long time can draw questions.

How TACS can help

TACS handles ASN requests as a sponsoring LIR and prepares the database objects alongside them. See ASN for registration, transfer and lease options, or run an ASN background check before taking over an existing number.