Open Infrastructure

Commented out the dhcp / ipv4 network:

[11:51:59] router1.place5:~# cat /etc/dhcp/dhcpd.conf 
option domain-name "place5.ungleich.ch";

default-lease-time 600;
max-lease-time 7200;

ddns-update-style none;

authoritative;

if exists user-class and option user-class = "iPXE" {
    filename "http://10.0.0.1/ipxescript";
} else {
    filename "undionly.kpxe";
}

# Internal
subnet 10.0.0.0 netmask 255.255.252.0 {
    range 10.0.1.0 10.0.3.254;
    option routers 10.0.0.1;
    option bootfile-name "undionly.kpxe";
    next-server 10.0.0.1;
    option domain-name-servers 10.0.0.3, 10.0.0.4;
}

# Co-working
#subnet 10.0.8.0 netmask 255.255.252.0 {
#    range 10.0.9.0 10.0.11.254;
#    option routers 10.0.8.1;
#    option domain-name-servers 10.0.8.3, 10.0.8.4;
#}

Restarted dhcpd, reconnected with a client, all good.