howto/Getting-started.md
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The current guideline is to allocate a /25 or smaller by default, keeping space for up to a /23 if possible. Don't allocate more than a /23 worth of addresses and please **think before you allocate**: If you are going to have 2-3 servers and two VPN-spaces, a /26 is enough to suit your needs. Same will go for most home-networks. This is not public internet, but our IPv4-space is valuable too!
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+To register for example 172.20.150.0/26, you need to fill in 172.20.150.0-172.20.150.63.
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**Note:** Reverse DNS works with _any_ prefix length, as long as your [recursive nameserver](/services/DNS) supports [RFC 2317](https://www.ietf.org/rfc/rfc2317.txt). Don't go for a /24 _just to have RDNS_.
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If you want to register an [IPv6 prefix](/FAQ#frequently-asked-questions_what-about-ipv6-in-dn42), you can create an `inet6num` object. A single /48 allocation in [ULA space](https://www.sixxs.net/tools/grh/ula/) will likely provide more than enough room for all devices you will ever connect. Some people use “vanity” prefixes like fd42:23:_xyz_::/48 instead of the fully standard-conformant pseudorandom ones.