stuck up record in DNS

[Nepryakhin Ivan]

hi guys!

I'm encountered with a strange issue:

 - host with  the name host12-c12-1 one time requested and  get the  address 10.10.10.12
 - dhcpd correct doing records ( A and PTR ) in  DNS
 - BUT after host shutdown and in the file dhcpd.leases line "binding state" become in the "free" - records A and PTR staying stuck in the base of DNS.



from https://linux.die.net/man/5/dhcpd.conf#Dynamic%20Dns%20Updates
i thinking  what DHCP- DDNS work in the next scheme:

 - HOST doing request for ip  address
 - DHCP  getting request and try write RR's A and PTR in DNS
 - DHCP give out ip address and do a record in the file dhcpd.leases
 - when time lease expire  DHCP remove RR's A and PTR from DNS

Please give me vector for a searching or suggestion about mistakes.


Thanks!!

P.S unfortunately i can't upgrade my environment



Environment:


isc-dhcp42-server-4.2.6_1
bind-base-9.9.5_8


cuted of the file dhcpd.lease:

lease 10.10.10.12 {
  starts 5 2019/08/09 11:00:47;
  ends 5 2019/08/09 12:00:47;
  tstp 5 2019/08/09 12:00:47;
  cltt 5 2019/08/09 11:00:47;
  binding state free;
  hardware ethernet 18:10:2b:12:db:12;
  uid "\001\010\000'\216G\220";
}

cuted from the file /etc/named/tsc/tsc.zone:

$TTL 1800       ; 30 minutes
host12-c12-1    A    10.10.10.12  
                        TXT     "00ffa9c88e143752544ac44exxxxxxxxxx"
      




cuted of the file dhcpd.conf:

## DDNS related configuration

ddns-update-style interim;
ddns-rev-domainname "in-addr.arpa.";
ddns-domainname "tsc.";
update-static-leases on;

group {

        option routers 10.10.10.1;
        ddns-hostname = host-decl-name;

        update-optimization false;
        update-conflict-detection false;
       

# example host
            host host12 {
                hardware ethernet 18:31:BF:xx:xx:xx;
                fixed-address 10.10.10.111;
        }
       
}





       

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[Simon Hobson]

Nepryakhin Ivan <[hidden email]> wrote:

> I'm encountered with a strange issue:

See below - it's "correct" operation for your example

> cuted of the file dhcpd.conf:
>
> ## DDNS related configuration
>
> ddns-update-style interim;
> ddns-rev-domainname "in-addr.arpa.";
> ddns-domainname "tsc.";
> update-static-leases on;
>
> group {
>
>         option routers 10.10.10.1;
>         ddns-hostname = host-decl-name;
>
>         update-optimization false;
>         update-conflict-detection false;
>        
>
> # example host
>             host host12 {
>                 hardware ethernet 18:31:BF:xx:xx:xx;
>                 fixed-address 10.10.10.111;
>         }
>        
> }

Where you have a host entry, the lease does NOT go through the normal lifecycle - and would not normally appear in the leases file.
Without the "update-static-leases on" statement, there would be no DNS update at all. With it, the DNS will be updated every time the host is leased that address - but those DNS records are never removed. Normally, the admin would be expected to add their own DNS entries to match host entries - the "update-static-leases on" statement is really just to save work.

If you want a "fixed" address for a host, and you want the DNS to be added/removed as required, then there is one option available. Add the "reserved" flag to a lease for the host - this fixed the lease so that it will not be allocated to another host. The lease is in all other respects the same as any dynamic lease.

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