Dynamic DNS + DHCP.

ElMoRsA · 09-08-2007, 02:50 PM

I'm currently running bind 9.3.4 and isc-dhcp 3.0.4 under Debian. I have managed to get DDNS working, and the first time they connect they get added to the reverse and forward zone OK:

DHCPREQUEST for 10.1.130.253 from 00:18:fe:9b:5a:05 via eth2
DHCPACK on 10.1.130.253 to 00:18:fe:9b:5a:05 (impre03B04) via eth2
Added new forward map from ws7186.example.com to 10.1.130.254
added reverse map from 254.130.1.10.in-addr.arpa. to ws7186.example.com

The thing is that this dhcp + ddns will be working within a huge network with different vlans (one vlan per floor). So imagine a printer, which is configured to obtain IP via DHCP, moves from one floor to another. The thing is that this entry WONT be updated, it will just say:

DHCPDISCOVER from 00:18:8b:19:75:63 via 10.1.112.1
DHCPOFFER on 10.1.112.254 to 00:18:8b:19:75:63 (ws7186) via 10.1.112.1
Forward map from ws7186.example.com to 10.1.112.254 FAILED: Has an A record but no DHCID, not mine.

(Notice the IP changed between them).

The thing is the forward zone is never updated, it keeps getting that "Has an A record but no DHCID, not mine" error.
Is there a way dhcpd could delete the previous entry and add the new updated one ?.

I will now paste my relevant parts of dhcpd.conf:

ddns-update-style interim;
deny-client-updates;
ddns-updates on;
update-static-leases on;
ddns-ttl 1;
one-lease-per-client on;
# allow unknown-clients;
ddns-domainname "bsas.example.com";
ddns-rev-domainname "in-addr.arpa.";
# authoritative;
do-forward-updates on;
# ddns-update-style interim;
# ddns-ttl 30;
# update-static-leases on;

And this is my named.conf:

(The dynamic zone being updated):

zone "bsas.example.com" {
type master;
file "dynamic/bsas.example.com";
# allow-update { key "rndc-key"; };
allow-transfer { key "rndc-key";
internal-servers;
mrecar-servers;
};

update-policy {
grant * self * A TXT;
};

I don't thing anything else from named.conf as i have already test it with nsupdate and have no issue at all deleting/adding new entries to the reverse and forward zones.

Any help would be VERY appreciated.

Regards, Francisco.

andrewdodsworth · 09-09-2007, 01:47 PM

Have you tried making the lease times shorter?

ElMoRsA · 09-10-2007, 11:14 AM

Quote:

Originally Posted by andrewdodsworth

Have you tried making the lease times shorter?

I have set the default values VERY low:

default-lease-time 600;
max-lease-time 6400;

Still not udpdating the hosts ip's.

You think that if the lease finishe's then it should delete the entry on the forward record and add it again ?

Regards,
Francisco

andrewdodsworth · 09-10-2007, 12:41 PM

I thought that would happen. Had a look at my own confs and read the man pages. I think possibly, unless your syntax is totally different that

Quote:

deny-client-updates;

should be

Quote:

ignore client-updates;

. In any case in my setup I have 'allow client-updates;' Apart from trying that I'm out of suggestions - my setup is very simple - single DHCP/DNS server.

ElMoRsA · 09-10-2007, 02:17 PM

Quote:

Originally Posted by andrewdodsworth

I thought that would happen. Had a look at my own confs and read the man pages. I think possibly, unless your syntax is totally different that
should be . In any case in my setup I have 'allow client-updates;' Apart from trying that I'm out of suggestions - my setup is very simple - single DHCP/DNS server.

I've found that both syntax's are similar, and they both cause the same effect. Indeed this didn't make the dynamic dns to work neither, but at least i got a better dhcpd.conf =)

Now i've found that the function of dynamic dns is given by dhcpd.conf scripting.

I reached this website: where they say that this code would do the trick. I have already added it to the dhcpd.conf but with no luck at all. Maybe im missing something for the forward zone as the reverse is working great with this patch:

Code:

option oe-key     code 159 = string;
option oe-gateway code 160 = ip-address;

on commit {     
  if (not static and
      ((config-option server.ddns-updates = null) or
       (config-option server.ddns-updates != 0))) {

      if exists oe-key {                                            
        set ddns-rev-name =                                                 
           concat (binary-to-ascii (10, 8, ".",                            
                                     reverse (1, leased-address)), ".",     
                    pick (config-option server.ddns-rev-domainname,         
                          "in-addr.arpa."));

        set full-oe-key = option oe-key;

        switch (ns-update (delete (IN, 25, ddns-rev-name, null),
                            add (IN, 25, ddns-rev-name, full-oe-key,
                                lease-time / 2)))           
        {                                                           
        default:                                                    
          unset ddns-rev-name;                              
          break;                                                    
        case NOERROR:                                       
          on release or expiry {                                    
            switch (ns-update (delete (IN, 25, ddns-rev-name, null))) {
            case NOERROR:                               
              unset ddns-rev-name;                                  
              break;                                        
            }                                               
          }
        }                                                           
      }
  }                                                         
}

And now I get:

dhcpd: if ws7186.example.com IN TXT "31689186b29fce25f991728d8ec3e3b2af" rrset exists and ws7186.mrec.ar IN A 10.1.125.254 rrset exists delete ws7186.example.com IN A 10.1.125.254: success.
dhcpd: if ws7186.example.com IN A rrset doesn't exist delete ws7186.example.com IN TXT "31689186b29fce25f991728d8ec3e3b2af": success.
dhcpd: removed reverse map on 254.125.1.10.in-addr.arpa.

I insist that i've already probed that i can update any entry on the zone's, adding or deleting via nsupdate.

Thanks again,

Francisco

Chrinux · 12-02-2010, 06:37 PM

Try this DHCP option
update-conflict-detection false;