Why Migrate?

ISC ceased maintaining ISC DHCP in 2022. The software may continue to work
in your environment indefinitely, but at some point you will need to upgrade
the operating system on the servers running dhcpd, and you may encounter
problems. It is impossible to predict when this will happen, so it is
important to develop a migration plan as soon as possible.

The Kea DHCP server is a completely new design, which benefited from some
lessons learned from supporting ISC DHCP for nearly three decades.

Many optional features are implemented as hook libraries, and the DHCPv4,
DHCPv6, and Dynamic DNS applications are separate packages, so you need
only
install the software you plan to use.
The extensive Kea API supports integration into your existing management
systems and online reconfiguration.
Components that are frequently modified, such as host reservations and
subnets, can optionally be stored in a common off-the-shelf database,
separate from the main Kea configuration file, using premium hooks.
Kea supports a simpler high availability mode in place of the DHCPv4
failover draft implemented by ISC DHCP. The Kea HA mode works equally well
for both DHCPv4 and DHCPv6.
Kea is multi-threaded, and offers much higher performance than ISC DHCP on
modern computers.
There is an Administrative Reference Manual for Kea (ISC DHCP just had man
pages).
There is an open source monitoring and configuration tool, called Stork,
for Kea users.

Migration provides an opportunity to learn more about aspects of your
network and your DHCP configuration that may not have been touched in a
while. As a result, your configuration may become simpler and cleaner.
Migration also gives you a chance to document the new configuration,
something which can often get overlooked.

Picture of a flock of birds in the sky, flying to the right


Planning Your Migration

Ideally, the best time to undertake a migration is when you already have
other changes going on, and it will be less disruptive to try something new.
For example, if you have already planned major infrastructure changes, you
are adding new office locations, switching to a new network server OS, or
attempting to achieve new networked application security goals, any of those
might present a good opportunity for migration.

Since migration can be a daunting process, ISC recommends several small- to
mid-sized migrations over time rather than one large migration. One way to
get a quick idea of how hard it might be for you to migrate, is to try our
hosted KeaMA tool for translating an ISC DHCP dhcpd.conf file to a Kea
configuration file. This is doesn’t require any committment and is easy -
and the result will indicate how straightforward migrating that DHCP server
will be.



Recommended Steps for a Successful Migration

Review the current network design and DHCP configuration file(s).
Set up an experimental Kea server in a non-production environment to
familiarize yourself with the software.
Review the Kea documentation to decide whether you want to use any features
implemented in hook libraries. Acquire any premium hook libraries you plan to use.
If you have a very simple deployment, take a look at our template
configuration for a single-site organization.
Determine which segment of the network to migrate first. Frequently
administrators will choose a network with fewer human users (e.g. a server
segment) and fewer legacy devices, which may have non-standard requirements
and behavior.
Use the Kea Migration Assistant on-line or download and run Kea Migration
Assistant locally to prepare a rough initial configuration file for the new
server from the existing ISC DHCP configuration file.
Review and modify the configuration file produced by the tool, paying
particular attention to the configuration of backup or load-balancing
partner services, and client classification and option configuration. The
Kea Migration Assistant will add log messages for any sections of the ISC
DHCP configuration it could not translate: review the linked descriptions of
differences between the two applications from your KeaMA log messages. Load
the resulting candidate configuration into a Kea instance and run the
configuration checkers to ensure you have a valid Kea configuration.
Test the resulting Kea configuration in a non-production environment, using
the software and OS versions you plan to deploy. ISC’s perfdhcp tool may
be helpful for generating simulated client traffic for testing.
Schedule the cutover for an off-peak, lower-traffic time and notify users
(if that is your process).
Translate your current valid DHCP leases into the Kea lease file format
using the KeaMA Lease tool. Load the resulting lease file into your target
Kea server.
Cutover by some combination of lowering the lease lifetimes for the devices
that will be migrating, re-configuring your relays to relay to the new DHCP
server, moving the subnets to be migrated to the new server, or entirely
decommissioning the old server.
Some more steps here (we don’t know everything!)
Verification, documentation
Rinse and repeat with other network segments



Resources

The best resource is often other users. We highly recommend asking for
advice on the kea-users mailing list and/or the dhcp-users mailing list.



Kea Configuration Differences

For a complete list of the known ISC DHCP configuration elements that do not
translate cleanly to an equivalent Kea configuration, search in the Kea
project repository for issues tagged with the “migration” label.

The major configuration areas that will likely require redesign are the
failover or high-availability solution, client classification, and host
reservations. Kea has an alternative to the DHCPv4 failover draft
implemented in ISC DHCP: the Kea feature is called “High Availability,”
and it works equally well for both DHCPv4 and DHCPv6. Kea does support
client classification, but there is no equivalent for ISC DHCP’s hyper
-flexible permit/deny scripting language. The option inheritance hierarchy
in Kea is different than in ISC DHCP, and the configuration for custom
vendor-specific options is also different. Kea has robust support for host
reservations, but in ISC DHCP all host reservations are global; in Kea,
host
reservations are by default per-subnet, although global host reservations
are also supported.

The following Knowledgebase articles may help with understanding Kea
functionality compared with ISC DHCP’s older features:

Kea High Availability vs ISC DHCP Failover (comparison)
Kea Configuration Introduction
Understanding Client Classification in Kea



Kea Migration Assistant - DHCP Configuration

ISC has developed the Kea Migration Assistant (KeaMA) tool to make it
easier
for users to translate their configuration files from one format to the
other. KeaMA is a branch of the legacy ISC DHCP server and is available at
https://gitlab.isc.org/isc-projects/dhcp/tree/master/keama. It takes the
existing local ISC DHCP configuration and outputs it as a Kea JSON
configuration. As mentioned above, some configuration elements cannot be
translated by machine, and will require hand-editing. These are noted in the
logs, with links to issues in ISC’s GitLab that explain the issue. See
this KB article on Migrating from ISC DHCP to Kea using the KeaMA tool.

Administrators need to run the tool once each for IPv6 and IPv4
configurations; KeaMA produces separate output files for each. KeaMA
provides diagnostic messages when a direct translation is not available or
possible, and provides a link to the related Kea GitLab issue.

The Kea Migration Assistant is included as part of the most recent ISC DHCP
versions. It can be built from source or installed as a pre-compiled
package
from ISC’s package repository.

Kea Migration Assistant packages
Kea Migration Assistant sources



Kea Migration Assistant - Leases

This experimental Python script takes an ISC DHCP lease file as input, and
outputs the same leases in the Kea lease file format. The leases then need
to be loaded into the target Kea server. Note that depending on how much
time elapses during this process, some of the leases may expire during the
migration period. The 2023 video below includes a demonstration of the
lease
migration tool (scroll to the end of the recording for the demo).

Kea Migration Assistant - leases repository




Video tutorials

ISC has conducted several webinars in an effort to help users migrating
from
ISC DHCP to Kea.

Migrating to Kea from ISC DHCP - 2020 This video, the 6th in a 2020 series
on using the Kea DHCP server, focuses on how to migrate to Kea from ISC
DHCP. Carsten Strotmann explains how to build and use the KeaMA
configuration migration tool.
Migrating to Kea from ISC DHCP - 2023 This 2023 video focuses on the higher
-level planning for a migration, and includes a demonstration of the lease
migration tool.
Creating a Kea configuration from an ISC DHCP configuration - 2019 In this
video, Alan Clegg covers using the KeaMA utility to create a Kea
configuration from an ISC DHCP configuration.
NANOG 76 talk on DHCP Migration to Kea