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Docker - DHCP Server
Since mid 2023 I have been running a Docker ISC Kea Image using base Docker Alpine Linux images, with S6 init system. (ISC Kea is a modern replacement for their DHCP.) The main DHCP server runs on my main server and I have an automatic fall over back up on my separate Linux router. I basically followed the Kea template Home Network of a Power User. I was never quite sure I had the automatic fall over back-up working. On 2023-01-02 I modified a configuration file on the primary server with a syntax error, 8 days later I notice millions of lines of errors on my log files. Sure enough the backup had simply been working. I fixed up the simple syntax error and the primary server took back over. Everything basically worked as expected.
ISC also has a project for a simple GUI interface primarily for Kea and basic for Bind9. There is apparently no Alpine package yet for Stork.
ISC-Kea seems to be provided in a number of packages
Package | Descriptiion | Comment |
---|---|---|
isc-kea-admin | This package provides backend database initialization and migration scripts and a DHCP benchmark tool. If you are not using a database backend, you may not need this. | Not using a database backend at this time |
isc-kea-common | Common libraries for the ISC Kea DHCP server. Install this. | Need this. |
isc-kea-ctrl-agent | This package provides the REST API service agent for Kea DHCP. | ? |
isc-kea-dev | Development headers for ISC Kea DHCP server. Install if you plan to create any custom Kea hooks. | Probably do not need. |
isc-kea-dhcp4-server | DHCPv4 server. | Need this. |
isc-kea-dhcp6-server | DHCPv6 server. | Do not need at this time. |
isc-kea-dhcp-ddns-server | DDNS server. | Need this. |
isc-kea-doc | Kea documentation. Highly recommended. | On a Docker container? |
isc-kea-hook-flex-option | Flexible Options hook. | What is this? |
isc-kea-hook-ha | High Availability hook. | What is this? |
isc-kea-hook-lease-cmds | Lease Commands hook. | What is this? |
isc-kea-hook-mysql-cb | MySQL Configuration Backend. | Dont need this at this time. |
isc-kea-hook-pgsql-cb | PostgreSQL Configuration Backend. | Dont need this. |
isc-kea-hook-stat-cmds | Statistics Commands hook. | ? |
isc-kea-http | This package is essential, install it. | It is essential… |
isc-kea-perfdhcp | Optional. Includes a DHCP performance testing tool from ISC. | ? |
isc-kea-shell | Text client for Kea DHCP Control Agent. | ? |
Network Ports
From IANA Service Name and Transport Protocol Port online Number Registry:
bootps 67 {tcp, udp} Bootstrap Protocol Server (DHCP) bootpc 68 {tcp, udp} Bootstrap Protocol Client (DHCP)
The Kea Control Agent uses port 8000 by default, but that value can be manually defined in its configuration file. (Usually located at /etc/kea/kea-ctrl-agent.conf.) This port needs to be open and accessible on every server that hosts a Kea DHCP service and a Kea Control Agent.
Docker Network Type
This is a good case where the Docker network type needs to be set to host. The DHCP server needs to be directly on the host to function.
DHCP testing
sudo nmap --script broadcast-dhcp-discover
will test the DHCP servers on the same network.
Reference
main dhcp4
kea-dhcp4 -t /app/dhcpv4.conf
to test the kea-dhcp4 configuration files/app/dhcpv4.conf
kea-dhcp4 -c /app/dhcpv4.conf
to start kea dhcp4 using configuration file/app/dhcpv4.conf
kea-dhcp4 -c /app/dhcpv4_plus.conf
to start kea dhcp4 using configuration file/app/dhcpv4_plus.conf
. This configuration file is designed to work with the kea control agent setup. Where as the basic configuration/app/dhcpv4_basic.conf
is not.
ctrl-agent -t /app/kea-ctrl-agent.conf
kea-ctrl-agent -t /app/kea-ctrl-agent.conf
to test the kea-cont-agent configuration file/app/kea-ctrl-agent.conf
kea-ctrl-agent -c /app/kea-ctrl-agent.conf
to start the kea-cont-agent configuration file/app/kea-ctrl-agent.conf
Kea logging
I have stored log files in the .config directory that is a Docker mounted volume for persistence and easy external viewing outside container. The following logs files can be seen.
.config/log/kea-dhcp4-commands.log
.config/log/kea-dhcp4-dhcpsrv.log
.config/log/kea-dhcp4-leases.log
.config/log/kea-dhcp4.log
.config/log/kea-dhcp4-ha-hooks.log
Kea Miscellaneous
docker attach kptr-kea-1
to attach to running containerkea-dhcp4 -v
To check running version
DNSSEC
My DNS server is a recursive caching type only. It take local (LAN) DNS queries and answers directly for any LAN name resolution, checks the cache for any external name resolution and then if not found, checks the specified external DNS servers to resolve names. My DNS server is not setup as a public DNS server and is not publicly accessible. Hence DNSSEC is not relevant for this local DNS server query validation.
For external name resolution Bind9 basically now defaults to automatic use of DNSSEC. This can be validated with (How To Test A Recursive Server) using:
dig @192.168.1.14 ftp.isc.org. A +dnssec +multiline
, the query return flagad
indicates the DNS answer returned a validated answer.dig @192.168.1.2 ftp.isc.org. A +dnssec +multiline
Equally important the following commands helps confirm that
dig @192.168.1.14 www.dnssec-failed.org A +cd
dig @192.168.1.2 www.dnssec-failed.org A +cd
Basic Bind9 DNSSEC configuration options
- The option (in
/etc/bind/named.conf.options
)dnssec-enable yes;
is no longer valid and use will cause error. DO NOT USE!
reference
DNS over TLS (DoT)
References
- KPTree.net's bare metal implementation of dns - dhcp, based upon ISC Bind9 and DHCP on Debian 10 (was originally Ubuntu).
- ISC documentation