== Preparation

It is necessary to consider the requirements for the installation in order to
devise an efficient and manageable set up.

=== Understand the network topology

When multiple networks (VLANs) are in use consideration must be given to how
the correct "pool" (IP address ranges) from which to allocate addresses is
identified.

The policy for setting specific DHCP options (e.g. lease time, default gateway,
time server and vendor-specific parameters) for different groups of hosts,
based on their network or some device attributes either supplied in the DHCP
requests or determined by dynamic lookup, should be well defined and
understood.

Other DHCP servers may implement implicit assumptions about the requirement of
your network topology and silently define particular behaviours, such as the
selection of IP address pool for a request based on a relay address. Some of
these behaviours must be specifed explicitly when using FreeRADIUS.

=== Choose a database backend

FreeRADIUS stores its leases in an SQL database, so one of the key decisions to
make is which database to use.

FreeRADIUS supports:

  * SQLite
  * PostgreSQL
  * MySQL / MariaDB
  * Microsoft SQL Server
  * Oracle

In most configurations the SQL database is likely to be the limiting component
that restricts the IP allocation throughput of the overall system. Each
database server has its own performance characteristics and unique approach to
features such as high-availability.

The choice of database should be made carefully based on the performance and
high-availability requirements of the system, as well as any prior experience.

[TIP]
====
SQLite is an in-process database that uses the local file system, is simple to
configure and is suitable for smaller installations. However, users with larger
address pools or high availability requirements should choose one of the other
standalone databases based on criteria such as performance, features,
familiarity and your need for commercial support.
====

FreeRADIUS ships with a default database schema and set of queries for each
supported database.  These are sufficient for most DHCP deployments but can be
reviewed and modified as required to suit a particular situation, for example
to customise the IP allocation policy such as by disabling address
"stickiness".

Now xref:protocols/dhcp/enable.adoc[enable the DHCP service].