inconsistent ddns behaviour

[Rick Dicaire]

Hi folks, ISC dhcpd 4.3.4, named 9.11.0-P3.
I have a ddns configuration that works fine.
Then I added a new subnet declaration (192.168.18.0) to the conf file, and
this subnet conf sent ddns updates as well though I didn't define dns zones
to update.

Is this expected behaviour?

Here's full dhcpd.conf

# dhcpd.conf
#
# Configuration file for ISC dhcpd (see 'man dhcpd.conf')
#
log-facility local6;
ddns-update-style interim;
ddns-ttl 1800;

ddns-hostname = pick (option fqdn.hostname, option host-name, concat
("ddns-", binary-to-ascii (10, 8, "-", leased-address)));

option host-name = config-option server.ddns-hostname;

include "/var/named/etc/Kgw-ddns.+157+20451.private";

shared-network DA {

subnet 192.168.15.0 netmask 255.255.255.0 {}

subnet 192.168.17.0 netmask 255.255.255.0 {
  interface eth1;
  authoritative;
  deny bootp;
  pool {
        range 192.168.17.100 192.168.17.200;
        option broadcast-address 192.168.17.255;
        default-lease-time 86400;
        option domain-name "dhcp.ldev";
        option domain-search "dhcp.ldev","ldev";
        option domain-name-servers 192.168.15.1,192.168.15.13;
        option ntp-servers 192.168.15.1;
        option routers 192.168.17.1;
                ddns-domainname "dhcp.ldev.";
                ddns-rev-domainname "in-addr.arpa.";
        allow unknown-clients;
        zone 17.168.192.in-addr.arpa {
          primary dns1.ldev;
                  key gw-ddns;
        }

        zone dhcp.ldev {
          primary dns1.ldev;
                  key gw-ddns;
        }
       }
    }
}

subnet 192.168.18.0 netmask 255.255.255.0 {
  interface wlan0;
  authoritative;
  deny bootp;
  pool {
        range 192.168.18.100 192.168.18.200;
        option broadcast-address 192.168.18.255;
        default-lease-time 86400;
        option domain-name "dhcp.ldev";
        option domain-search "dhcp.ldev","ldev";
        option domain-name-servers 192.168.15.1,192.168.15.13;
        option ntp-servers 192.168.15.1;
        option routers 192.168.18.1;
        allow unknown-clients;
        }
}

>From syslog:

March 26th 2017, 14:33:39.000 Mar 26 14:33:39 dns1 dhcpd: DHCPOFFER on
192.168.18.100 to f0:db:f8:46:50:2e (Richards-iPad) via wlan0
March 26th 2017, 14:33:40.000 Mar 26 14:33:40 dns1 dhcpd: DHCPREQUEST for
192.168.18.100 (192.168.18.1) from f0:db:f8:46:50:2e (Richards-iPad) via
wlan0
March 26th 2017, 14:33:40.000 Mar 26 14:33:40 dns1 dhcpd: DHCPACK on
192.168.18.100 to f0:db:f8:46:50:2e (Richards-iPad) via wlan0
Mar 26 14:33:40 dns1 named[1423]: client @0x7f56c816a8e0
192.168.15.1#43225/key gw-ddns: signer "gw-ddns" approved
Mar 26 14:33:40 dns1 named[1423]: client @0x7f56c816a8e0
192.168.15.1#43225/key gw-ddns: updating zone 'dhcp.ldev/IN': adding an RR
at 'Richards-iPad.dhcp.ldev' A 192.168.18.100
Mar 26 14:33:40 dns1 named[1423]: client @0x7f56c816a8e0
192.168.15.1#43225/key gw-ddns: updating zone 'dhcp.ldev/IN': adding an RR
at 'Richards-iPad.dhcp.ldev' TXT "311db3af593e1db80ce9679a0248b51c64"
Mar 26 14:33:40 dns1 dhcpd: Added new forward map from
Richards-iPad.dhcp.ldev to 192.168.18.100
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