IPv4 Private Address Space

[Louis Garcia]

On Tue, May 11, 2021 at 5:51 PM Thor Simon <Thor.Simon at twosigma.com> wrote:
>
> 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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> _______________________________________________
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>
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Currently I have three networks 172.16.2.0/24 172.16.3.0/24
172.16.4.0/24. I read that not all of 172.16.0.0 is private, only
172.16.0.0/12. I am trying to not have public routable IPs on my
network. Please let me know if this setup is fine.

          # DHCP Server Configuration file.

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

          # Client system architecture type: RFC4578
          option arch code 93 = unsigned integer 16;

          subnet 172.16.2.0 netmask 255.255.255.0 {
                      option domain-name-servers 172.16.2.1;
                      option broadcast-address 172.16.2.255;
                      option routers 172.16.2.1;
                      option ntp-servers 172.16.2.1;
                      range 172.16.2.50 172.16.2.254;
                      if option arch = 00:07 {
                            filename "/grub/shim.efi";
                      }
                      next-server 172.16.2.5;
          }

          subnet 172.16.3.0 netmask 255.255.255.0 {
                      option domain-name-servers 172.16.3.1;
                      option broadcast-address 172.16.3.255;
                      option routers 172.16.3.1;
                      option ntp-servers 172.16.3.1;
                      range 172.16.3.50 172.16.3.254;
          }

          subnet 172.16.4.0 netmask 255.255.255.0 {
                      option domain-name-servers 172.16.4.1;
                      option broadcast-address 172.16.4.255;
                      option routers 172.16.4.1;
                      option ntp-servers 172.16.4.1;
                      range 172.16.4.50 172.16.4.254;
          }