cannot update ddns from client.

hi to all, I've centos7.5 as server and client and one centos6.10 client.
I know that this question is much simmilar to another question asked by me but it is slightly diffrent
and I am asking this one:-

i am trying to configure ddns server and client. mine named.conf is :-

Code:options {
listen-on port 53 { 127.0.0.1; 192.168.40.1; };
// listen-on-v6 port 53 { ::1; };
directory "/var/named";
dump-file "/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
memstatistics-file "/var/named/data/named_mem_stats.txt";
allow-query { localhost; 192.168.40.0/24; };
// recursion yes;

dnssec-enable yes;
dnssec-validation yes;

/* Path to ISC DLV key */
bindkeys-file "/etc/named.iscdlv.key";

managed-keys-directory "/var/named/dynamic";

pid-file "/run/named/named.pid";
session-keyfile "/run/named/session.key";
};

controls {
inet 127.0.0.1 port 953
allow {127.0.0.1;} keys {"rndc-key";};
};

logging {
channel default_debug {
file "data/named.run";
severity dynamic;
};
};

zone "." IN {
type hint;
file "named.ca";
};

include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";
include "/etc/rndc.key";

zone "db.net" IN {
type master;
file "dynamic/db.net.frd.zone";
allow-update { key "rndc-key"; };
};

zone "40.168.192.in-addr.arpa" IN {
type master;
file "dynamic/db.net.rev.zone";
allow-update { key "rndc-key"; };
};mine dhcpd.conf is

Code:option domain-name "db.net";
option domain-name-servers 192.168.40.1;

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

allow client-updates;

include "/etc/rndc.key";

ignore client-updates;

ddns-domain="db.net";
ddns-rev-domain="40.168.192.in-addr.arpa";
ddns-updates on;

ddns-update-style interim;
authoritative;

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;

subnet 192.168.40.0 netmask 255.255.255.0 {
range 192.168.40.10 192.168.40.50;
option domain-name-servers server75ddns.db.net;
option domain-name "server75ddns.db.net";
option routers 192.168.40.1;
option broadcast-address 192.168.40.255;

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

zone db.net. {
primary 192.168.40.1;
key "rndc-key";
}

zone 40.168.192.in-addr.arpa. {
primary 192.168.40.1;
key "rndc-key";
}forward zone :-
Code:$ORIGIN .
$TTL 86400 ; 1 day
db.net IN SOA db.net. admin.db.net. (
18 ; serial
86400 ; refresh (1 day)
3600 ; retry (1 hour)
604800 ; expire (1 week)
10800 ; minimum (3 hours)
)
NS server75ddns.db.net.
$ORIGIN db.net.
server75ddns A 192.168.40.1
$ORIGIN server75ddns.db.net.
$TTL 300 ; 5 minutes
centos7clientddns A 192.168.40.11
TXT "001bff74691f65a224a6171115899b6879"
centos6clientddns A 192.168.40.10
TXT "002eb44baed6a8ae2316b7d2d37c090fb2"reverse zone :-
Code:$TTL 1D
@ IN SOA db.net. admin.db.net. (
10 ; serial
1D ; refresh
1H ; retry
1W ; expire
3H ) ; minimum
@ IN NS server75ddns.db.net.
1 IN PTR server75ddns.db.net.problem is that 1. as you can see in forward zone, it is updated by ddns but reverse zone is not updating. 2. I can not ping or dig or host from clinet to server but i can ping from server to client via only ip addressing. after some tme ( I don't know really how it was happen) client6clientddns.db.net has chnaged ipaddress to 192.168.40.12 but that was not updation of ipaddress 192.168.40.12, and 192.168.40.11 is not pinggable. I installed "ddclient " on both of clinents. after installation of rpm i ran this command :-
Code:[root@centos6clientddns etc]# dhclient -r
[root@centos6clientddns etc]# dhclient but no effect.

please solve my problem.