[Solved] DHCP server does not recognize subnet declaration

[toquinho]

Hello,

I want to use a laptop with a wireless and a wired network interface to set up a separate subnet that only the laptop can see. The interfaces are enp4s0 and wlp2s0:

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root@FENCHURCH:~# netstat -i
Tabela de Interfaces do Kernel
Iface      MTU    RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
enp4s0    1500        0      0      0 0             0      0      0      0 BMU
lo       65536        0      0      0 0             0      0      0      0 LRU
wlp2s0    1500     3377      0      0 0          1598      0      0      0 BMRU

I want wlp2s0 to connect to my normal LAN, and the laptop is supposed to act as a DHCP server for the devices attached to enp4s0. So I installed isc-dhcp-server and removed dnsmasq-base, which was installed on the laptop. I edited /etc/default/isc-dhcp-server and /etc/dhcp/dhcpd.conf:

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root@FENCHURCH:~# more /etc/default/isc-dhcp-server 
INTERFACESv4="enp4s0"
INTERFACESv6=""

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option domain-name "mysubnetwork.org";
option domain-name-servers 8.8.8.8;
default-lease-time 600;
max-lease-time 7200;
ddns-update-style none;

subnet 10.254.239.0 netmask 255.255.255.0 {
  interface enp4s0;
  range 10.254.239.15 10.254.239.50;
  option subnet-mask 255.255.255.0;
  option routers 10.254.239.10;
}
host fenchurch {
  hardware ethernet 54:42:49:fb:dc:c3;
  fixed-address 10.254.239.10;
}

When starting the DHCP server, I get the following error:

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abr 05 00:19:27 FENCHURCH isc-dhcp-server[1420]: Launching IPv4 server only.
abr 05 00:19:27 FENCHURCH dhcpd[1432]: Wrote 0 deleted host decls to leases file.
abr 05 00:19:27 FENCHURCH dhcpd[1432]: Wrote 0 new dynamic host decls to leases file.
abr 05 00:19:27 FENCHURCH dhcpd[1432]: Wrote 0 leases to leases file.
abr 05 00:19:27 FENCHURCH dhcpd[1432]: 
abr 05 00:19:27 FENCHURCH dhcpd[1432]: No subnet declaration for enp4s0 (no IPv4 addresses).
abr 05 00:19:27 FENCHURCH dhcpd[1432]: ** Ignoring requests on enp4s0.  If this is not what
abr 05 00:19:27 FENCHURCH dhcpd[1432]:    you want, please write a subnet declaration
abr 05 00:19:27 FENCHURCH dhcpd[1432]:    in your dhcpd.conf file for the network segment
abr 05 00:19:27 FENCHURCH dhcpd[1432]:    to which interface enp4s0 is attached. **
abr 05 00:19:27 FENCHURCH dhcpd[1432]: 
abr 05 00:19:27 FENCHURCH dhcpd[1432]: 
abr 05 00:19:27 FENCHURCH dhcpd[1432]: Not configured to listen on any interfaces!
abr 05 00:19:27 FENCHURCH dhcpd[1432]: 
abr 05 00:19:27 FENCHURCH dhcpd[1432]: If you think you have received this message due to a bug rather
abr 05 00:19:27 FENCHURCH dhcpd[1432]: than a configuration issue please read the section on submitting
abr 05 00:19:27 FENCHURCH dhcpd[1432]: bugs on either our web page at www.isc.org or in the README file
abr 05 00:19:27 FENCHURCH dhcpd[1432]: before submitting a bug.  These pages explain the proper
abr 05 00:19:27 FENCHURCH dhcpd[1432]: process and the information we find helpful for debugging.
abr 05 00:19:27 FENCHURCH dhcpd[1432]: 
abr 05 00:19:27 FENCHURCH dhcpd[1432]: exiting.
abr 05 00:19:29 FENCHURCH isc-dhcp-server[1420]: Starting ISC DHCPv4 server: dhcpdcheck syslog for diagnostics. ...
abr 05 00:19:29 FENCHURCH isc-dhcp-server[1434]:  failed!
abr 05 00:19:29 FENCHURCH isc-dhcp-server[1435]:  failed!
abr 05 00:19:29 FENCHURCH systemd[1]: isc-dhcp-server.service: Control process exited, code=exited, status=1/FAILURE

I am not sure if the host section in dhcpd.conf is required, but it does not make any difference. I am making these edits in a remote terminal from another computer in my LAN. The laptop is connected to the LAN via wlp2s0 and gets its IP from a DHCP server. Currently, nothing is connected to enp4s0 of the laptop.

Any help is of course greatly appreciated.

Thanks,

Toquinho

[p.H]

Did you assign an IP address in the 10.254.239.0/24 subnet to enp4s0 ?
What does "ip addr" show ?

[toquinho]

Thanks a lot. I had not assigned an IP to enp4s0. In hindsight it is obvious that this is necessary. I should have read https://wiki.debian.org/DHCP_Server to the very end.