FreeTransit Learning Centre

Practise BGP locally, then use DN42 as a realistic private routing environment without risking public announcements.

Build a safe lab and use DN42

The safest learning environment is one you can destroy and rebuild without affecting another network. Start locally. Use DN42 only after you can operate a small isolated BGP topology confidently.

Stage 1: Local and disposable

A useful lab should be:

• isolated from your production routing table;
• reproducible from configuration files;
• reachable through a separate management path;
• small enough that you can inspect every route;
• able to simulate failures and leaks;
• dual-stack, so IPv6 is not postponed indefinitely.

Recommended platforms:

• Open-source BGP configuration labs
• Containerlab
• FRRouting
• GNS3 where a graphical virtual topology is preferred

Stage 2: DN42

DN42 is a community-operated private network built with tunnels, BGP, DNS and other Internet technologies. It provides a place to practise peering, transit and distributed coordination with other operators.

DN42 is valuable because it behaves more like a real inter-domain network than a three-router lab. It is still a shared network, so mistakes affect other participants. Treat it as a training network, not as a consequence-free toy.

Start here

• DN42 overview
• Getting started
• FAQ
• DN42 registry
• Global Route Collector
• BGP communities in DN42

Important isolation rules

• Keep DN42 routes separate from the public Internet routing table. A dedicated VRF, network namespace or separate router is strongly preferred.
• Never redistribute DN42 routes into a public eBGP session.
• Never export public full-table routes into DN42.
• Build filters from the current DN42 registry rather than copying old prefix ranges from a blog post.
• Use only the resources assigned to you by the DN42 registry.
• Do not reuse your public ASN as a shortcut for DN42 registration.
• Apply explicit import and export filters to every DN42 peer.
• Set prefix limits even on a private training network.
• Document which peers are transit, peering or non-transit relationships.
• Monitor your advertisements through the DN42 route collector.

Suitable DN42 exercises

1. Register resources correctly in the DN42 registry.
2. Establish a WireGuard tunnel and eBGP session.
3. Announce one IPv4 and one IPv6 prefix.
4. Confirm your route in the global route collector.
5. Add a second peer and compare path selection.
6. Implement communities for link characteristics or policy.
7. Offer transit only after you can prevent accidental route leaks.
8. Run an internal service and test reachability through multiple paths.
9. Withdraw the route and confirm that remote visibility disappears.
10. Write a short incident note for a deliberately broken lab change.

Talks about DN42 and routing

• Routing and DN42 — Easterhegg 2010 — an early introduction to DN42 as a network for learning and practice.
• BGP und OSPF — FrOSCon 2016 — German-language explanation of Internet routing and experimenting through DN42.

These recordings are useful for concepts and history. Use the current DN42 wiki for present-day registration, addressing and configuration requirements.

DN42 is not production preparation by itself

DN42 teaches useful coordination and routing skills, but public operation also requires:

• accurate RIPE Database and IRR objects;
• RPKI ROAs;
• an accurate ASPA provider set;
• public abuse and NOC contacts;
• real monitoring from Internet route collectors;
• change control and rollback planning;
• filtering based on your actual provider and customer relationships.

Continue with the RIPE Database, RPKI and safe-operations pages before requesting a public BGP activation.