IPv4 Private Address Space

[Thor Simon]

What exactly are you trying to do?  There is not a /12 (255.240.0.0 netmask) of addresses available starting at 172.16.4.0 -- you have given the mask and broadcast address for the entire 172.16.0.0/12 containing range, but your subnet address is offset from the start of the containing netblock by 1024 addresses.  The DHCP server is entirely right to reject this nonsensical configuration.

Do you have an existing /22 at 172.16.0.0 that you're trying to work around?

Thor

-----Original Message-----
From: dhcp-users <dhcp-users-bounces at lists.isc.org> On Behalf Of Louis Garcia
Sent: Tuesday, May 11, 2021 5:39 PM
To: Users of ISC DHCP <dhcp-users at lists.isc.org>
Subject: IPv4 Private Address Space

According to standards set forth in Internet Engineering Task Force
(IETF) document RFC-1918, the following IPv4 address ranges are reserved by the IANA for private internets,

10.0.0.0/8 IP addresses: 10.0.0.0 – 10.255.255.255
172.16.0.0/12 IP addresses: 172.16.0.0 – 172.31.255.255
192.168.0.0/16 IP addresses: 192.168.0.0 – 192.168.255.255

dhcpd does not seem to like subnet/mask combination.

          authoritative;
          default-lease-time 600;
          max-lease-time 7200;
          subnet 172.16.4.0 netmask 255.240.0.0 {
                      option domain-name-servers 172.16.4.1;
                      option broadcast-address 172.31.255.255;
                      option routers 172.16.4.1;
                      option ntp-servers 172.16.4.1;
                      range 172.16.4.50 172.16.4.254;
          }

May 11 16:07:01 dhcpd[4540]: Internet Systems Consortium DHCP Server 4.4.2b1 May 11 16:07:01 dhcpd[4540]: Copyright 2004-2019 Internet Systems Consortium.
May 11 16:07:01 dhcpd[4540]: All rights reserved.
May 11 16:07:01 dhcpd[4540]: For info, please visit https://www.isc.org/software/dhcp/
May 11 16:07:01 dhcpd[4540]: /etc/dhcp/dhcpd.conf line 4: subnet
172.16.4.0 netmask 255.240.0.0: bad subnet number/mask combination.
May 11 16:07:01 dhcpd[4540]: subnet 172.16.4.0 netmask 255.240.0.0 May 11 16:07:01 dhcpd[4540]:
                    ^
May 11 16:07:01 dhcpd[4540]: Configuration file errors encountered -- exiting May 11 16:07:01 dhcpd[4540]:
May 11 16:07:01 dhcpd[4540]: This version of ISC DHCP is based on the release available May 11 16:07:01 dhcpd[4540]: on ftp.isc.org. Features have been added and other changes May 11 16:07:01 dhcpd[4540]: have been made to the base software release in order to make May 11 16:07:01 dhcpd[4540]: it work better with this distribution.
May 11 16:07:01 dhcpd[4540]:
May 11 16:07:01 dhcpd[4540]: Please report issues with this software via:
May 11 16:07:01 dhcpd[4540]: https://bugzilla.redhat.com/ May 11 16:07:01 dhcpd[4540]:
May 11 16:07:01 dhcpd[4540]: exiting.
May 11 16:07:01 dhcpd.service: Main process exited, code=exited, status=1/FAILURE _______________________________________________
ISC funds the development of this software with paid support subscriptions. Contact us at https://www.isc.org/contact/ for more information.

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