Egbert Networks

Systemd and ISC DHCP Client

This page is about using ISC DHCP client (`dhclient`) in systemd environment.

I must be one of the surviving user that uses both ISC dhclient and systemd.

Primarily because systemd DHCP cannot handle DHCP-Options (not options, but Options). The ones that Juniper JunOS DHCP server requires for Verizon FiOS.

So, here begins the long saga of a blog (that I might break up in several blogs)…

First thing first, to do an analysis of systemd unit inter-dependencies, I executed:

systemd-analyze dot --order \
    nginx.service network-pre.target network-online.target \
    network.target system-dhclient.slice
sys-subsystem-net-devices-eth1.device \
    networking.service nss-lookup.target shorewall.service bind9.service \
    dhclient@eth1.service  ddclient.service resolvconf.service
    system-dhclient.slice  \
    > /tmp/custom.gv

As one can see that most people don’t have dhclient@eth0.service systemd unit file.

We are going to create a .gv file and convert it to SVG as shown below:

dot -Tsvg < /tmp/custom.gv > /tmp/custom.svg
firefox /tmp/custom.svg

ISC DHCP CLient

And I finally got my very own Linux gateway to be hooked up to the Verizon HFC network, instead of using ActionTek wireless broadband router.

Details in here: https://github.com/egberts/systemd-dhclient

/etc/systemd/network/dhclient$.service

It is also possible to explicitly tell systemd-networkd to ignore a link by using Unmanaged=yes option, see systemd.network(5).