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dn42

1. What this is all about

As we all know, besides theory and reading, at some point, when you are learning something, you want and have to use what you have learned. This is the same with internet routing and advanced networking. To get active on the big "real" internet, there are some preconditions, you need one or more ISPs to peer with, a link you can use for the peering, a public ip range and also probably a public AS number. Meeting all these preconditions is probably expensive and takes some time and effort. Also, when getting active on the internet, you should already have some experience.

This is where dn42 comes in. dn42 is an internet which operates very similar to the internet, so most experience one gets in dn42 is applicable to the internet as well. The difference is that joining dn42 is free for everyone and does not create much cost, in most cases none at all.

2. Technical details

You are probably wondering how it is possible to build a more or less cost free internet. The answer is, dn42 hardly uses physical links between the single networks but virtual ones. These virtual links use the internet as transport but are logically independend from it, you can treat a virtual link more or less like a fiber or copper line. In dn42 openvpn is used very often, but also gre is in use. And if someone wants to build a physical link to another network he always is welcome to, these are just less common because of their cost and the effort needed.

The main ip range of dn42 is 172.22.0.0/15. The main AS numbers range from 64601 to 64855, where usually 172.22.1.0/24 is 64601, 172.22.2.0/24 is 64602 and so on. 172.23.0.0/16 is "reserved" but not yet in use. You may or may not have noticed that neither these ip ranges nor these AS numbers are public. They are reserved for private use. That means, many people use these for their own networks and those will never be used on the internet. Also as with the links, you may use your own public ip range if you have one, and you may also use your public AS number if you have one. It's just that more people happen to have no own ip or as number. The only drawback from using a private ip number is that this ip will never be reachable from the internet. The use of these ip and as numbers is coordinated and documented in the dn42 wiki.

Like the real internet, dn42 uses BGP to exchange routing information between different networks. Whether the networks use a routing protocol internally is left to each network's admin, but most networks are big enough that running an interior gateway protocol like ospf is actually helpful and makes things easier. Most people use standard hardware for their routers, as specialized hardware isn't exactly cheap. There are mainly four implementations for BGP on default hardware. The most common in dn42 is quagga, a fork of the - it seems - no longer maintained GNU zebra, which runs on most unizes from linux over *BSD to solaris. Also used in dn42 is openbgpd which runs on OpenBSD. There are also the "enterprise class" XORP and the simplicistic Bird, however those are not very common in dn42. There were also some boxes running JunOS, the Juniper Operating system, which is used with professional routing hardware. Feel free to try and use any implementation of BGP you consider adequate.

3. Status

At the moment, my filtered ipv4 routing table contains nearly 100 entries. Ipv6 is also used in dn42, here, everyone gets his own ip range from a tunnelbroker and anounces it in dn42, my v6 routing table contains about 40 entries, growing. Below you can see a graph of the current networks and the links between them. My humble self is nihilus, maintaining AS64692.

Image: Graph of dn42